Zach Flynn
2023-12-14 Thu 00:59


Table of Contents

1. Introduction

SLOBIL is easy to use interactively. It is natural to write line-by-line in the REPL and has a command-like syntax. SLOBIL programs can just be collections of functions executed in the SLOBIL REPL itself because it is a natural command syntax.

SLOBIL is a dynamically-typed language. You do not define new types in the language. Instead the language provides a few flexible types. The language has a prototype object system, i.e. reference instances of an object are used to create new instances and changes to parent instances cascade down the chain. In other words, you do not declare an object a member of class X. You say, this object is like that other object, except in these ways.

SLOBIL prioritizes what the caller of the code wants to do. Instructions, which would be functions or procedures in other languages, do not have fixed argument lists and users can modify other aspects of the instruction that, perhaps, the original author did not intend. The language gives you the sharp knife and lets you cut.

It is biased against strict encapsulation and towards flexibility for the end user.

It has superficial syntax similarities to Tcl in that the language is a command-based language that uses different types of parenthesis to do different things. Less superficially, similarly to Tcl, it lets everything be overwritten (with different semantics) and no keywords are reserved. The typing is much stronger than Tcl though, and the semantics of the two languages are different. The object system is prototype-based instead of the class-based system in Tcl.

2. The Language

Lexical Elements

Slots are represented by a forward-slash (/) followed by any non-whitespace characters. Slot names are case-sensitive. /a and /A refer to different slots. I use lower case names for slots with multiple words separated by hyphens. Like this: /a-name-for-a-slot. But the language allows for alternative naming conventions.

A literal number is a sequence of digits ([0-9]) that includes at most one decimal point represented by a period. It may also be preceded by a hyphen to indicate a negative number. A literal number contains no spaces.

A literal string is a sequence of characters where the first and last characters are double quotation marks. A literal string can contain the following escape sequences preceded by a backwards slash \.

  • \ outputs \.
  • t outputs tab
  • n outputs newline
  • r outputs carriage return
  • ' outputs a single quote character

A literal string outputs a double quotation mark when a single quotation mark is used '. A literal string can contain whitespace, including newlines.

A literal boolean value is a string of characters that is either True or False.

A literal nothing value is a string of characters that is Nothing.

A single apostrophe (') is a token that starts a comment which is ended by a new line.

The following characters are special tokens: [, (, {, ., }, ), ].

If a sequence of characters without any whitespace is (1) not a literal string, (2) not a literal number, (3) not a special token, (4) not a comment, (5) not a literal boolean, (6) not a literal nothing, and (7) does not begin with a forward slash, then it is considered a data reference. Some names that are valid for slots are not valid for data references. Data references refer to the data currently inserted in the slot with the same name.

SLOBIL programs are whitespaced-separated lists of the above tokens.

Data and Types

Programmers do not define types. The following are the data types: Integer, Real, String, Slot, Object, Instruction, Expression, Operation, File, Boolean, Nothing, and Task.

Integer's are numbers without decimal points. They are "big" and can be arbitrarily large in magnitude.

Real's are numbers with decimal points. They are double precision floating-points.

String's are UTF-8 encoded character strings. Internally, they are represented as UTF-32 strings for speed, but they output to UTF-8.

Slot's indicate the location of data and also can act as symbols. They are written by giving a name that begins with a forward-slash.

Object's can contain any number of slots and store data in these locations. Code is executed inside of objects and can refer to data located in the object's slots. Objects are represented internally as a hash table.

Instruction's are SLOBIL code objects that are executed only when the programmer explicitly requests their execution. They are the primary way programmers write functions, procedures, and methods. Instructions are created by enclosing code between the tokens ( and ).

Expression's are SLOBIL code objects that are executed whenever the programmer requests their value, i.e. they are lazy. Expressions are created by enclosing code between the tokens { and }.

Operation's are code objects that take a series of positional arguments. The built-in operations are written in C, but users can also define operations.

File's are stream objects used for writing to external files.

Boolean's are either True or False.

Nothing is the type for the literal nothing value Nothing. Nothing else has this type.

Task's are processes running on the computer. When the program starts, it is in the main task. Additional tasks can be created for multi-threaded programs.

File, Task, and Object data are passed by reference. All others are by value.

Statements and Objects

A statement is a list of whitespace-separated tokens ended by a .. Naturally, the tokens included in the list cannot include ..


Statements happen inside objects. The object a statement is executed in determines what data is returned by a data reference. Data references look for a value in the relevant slot in the current object, if none is found, then they look for an object in the slot in the object containing the current object and so on.

Statements are executed effectively inside temporary objects. Arguments in a statement generally determine the values located at slots in the temporary object.

Statements begin with an operation. There are a few exceptions to this rule where the operation is automatically-selected based on the data type used for the first argument. This is for convenience. The entire language can be accessed with statements that begin with an operation.

The obligatory first statement in SLOBIL:

... print "Hello, world!" .

Creating Objects

Objects are created by using the object operation, followed by an alternating sequence of slots and data elements.

... object /number 10 /string "Hello!" /real 3.2 .
ans = an Object with:
number of type Integer, value: 10
string of type String, value: "Hello!"
real of type Real, value: 3.200000

The object operation sets the /ans slot to the relevant object.

The /ans Slot

Each Object has a special slot called the /ans slot. Many built-in operations put data in the /ans slot. It is the standard place to return values from an instruction, operation, or expression. For example,

... add 4 5 .
ans = 9
... print ans .


Substatements are statements included as an element of another statement. They are surrounded by square brackets ([]) and executed in the order they appear in the statement prior to the statement itself being evaluated. When the outer statement is evaluated the substatements are replaced by the value each substatement set the /ans slot to after it was executed.

For example,

... object /number 10 /string "Hello!" /real 3.2 /object [ object /x 3 /y 2 ] .
ans = an Object with:
number of type Integer, value: 10
string of type String, value: "Hello!"
real of type Real, value: 3.200000
object of type Object, value: an Object with:
x of type Integer, value: 3
y of type Integer, value: 2
... add 5 [ add 4 3 ] .
ans = 12

Substatements do not need to include a . to end the last statement in the substatement. They can, but they do not have to. Substatements can include multiple statements.

The brackets can be placed right next to the other tokens. For example,

... add 5 [add 4 3] .
ans = 12

Will work, but the thing to keep in mind is that a sentence is not complete with a period until some whitespace follows the period. So this will not work.

... ' Will not work
... add 5 [add 4 3 .]
... 'Will work
... add 5 [add 4 3 . ]

So if you prefer putting parenthesis next to the other tokens, I recommend not including the . on the last statement.

I prefer always including spaces between the parenthesis and other tokens.

Inserting Data Into Slots

Slots determine the location of data. The set operation inserts data into a slot, like so:

... set /number 10 .
... print number .

The set operation takes the slot to insert to and the data to insert as arguments.

The second line in the above example, print number ., demonstrates how to access the data located at a slot. Simply omit the forward slash to get the data.

Because this is a common procedure in SLOBIL, if the first element of a statement is a slot, then SLOBIL assumes you want to call set. For example, the above could have been written as:

... /number 10 .

set has an optional third argument: the object whose slot we should insert the data into. If the third argument is omitted, then the value is inserted into the current object's slot.

... /rectangle [ object /length 10 /width 5 ] .
... print rectangle .
an Object with:
length of type Integer, value: 10
width of type Integer, value: 5
... /width 4 rectangle .
... print rectangle .
an Object with:
length of type Integer, value: 10
width of type Integer, value: 4

The move operation moves data between different slots without copying the data.

... /x "Hello." .
... print x .
... move /x /y .
... print y .
... print x .
Error: Value at slot /x not found.

The delete operation removes data from the slot.

... /x "Hello." .
... print x .
... delete /x .
... print x .
Error: Value at slot /x not found.


Instructions are a data type that contains code to execute. They are created by enclosing a series of statements in parenthesis. The last statement in the parenthesis does not have to end with a period.

For example:

... /add-one ( add t 1 ) .
... print add-one .
(  add t 1  )

The call operation calls an instruction in a temporary object determined by alternating slots and data values similar to the call to an object. In effect, instructions are called with named arguments.

... call add-one /t 4 .
ans = 5

When instructions execute, whatever data they set the /ans slot to in the temporary object in which they execute is sent back to the object from which they are called. No other slots they assign are modified in the current object.

... /circle-area
  /pi 3.1459 .
  /r2 [ power r 2 ] .
  mul r2 pi .
) .
... call circle-area /r 2
ans = 12.583600
... print ans.
... print pi .
Error: Value at slot /pi not found.
-> print pi .

Calling instructions is a common thing to do. So, if the first element of a statement is an instruction, SLOBIL assumes the programmer wants to call it.

... circle-area /r 2 .
ans = 12.583600

Instructions are just code, they do not carry an environment around with them. When the programmer call's an instruction, the programmer determines the environment the code is executed in. Instructions do not have a fixed set of arguments but allow the caller of the code to manipulate the environment in which they are called arbitrarily. For example:

... /add-one ( add t 1 ) .
... add-one /t 5 .
ans = 6
... add-one /t 5 /add sub .
ans = 4

Any non-literal in an instruction can be changed by adjusting the environment in which the code is executed.

To bind an instruction to an environment, you can use the bind operation. For example,

... /add2 ( add t s ) .
... bind add2 /t 3 .
... add2 /s 4 .
ans = 7

Getting data

The get operation sets the /ans slot to the data located at a certain slot.

... /x "Hello." .
... /y [ object /test "Goodbye." ] .
... get /x .
ans = "Hello."
... get /test .
... get /test y .
ans = "Goodbye."

The second argument to get is the object to get the data from. If it is omitted, the data is grabbed from the current object. There is also a shorthand notation for getting data from an object. The notation object:slot returns the data located at the slot within the object. The notation can also be nested like object:slot1:slot2 where another object is located at object:slot1.

... print y:/test .

One limitation to the colon notation is that it cannot be used with substatements.

... ' Will give an error
... print y:[ answer /test ] .

The exist operation tests whether data exists at a given slot in an object. Like get, it has an optional second argument to give the object. If the argument is omitted, it searches the current object. It sets the /ans slot to True if data exists at the slot and False if the data does not.

... exist /new-slot .
ans = False.
... /new-slot 0 .
... exist /new-slot .
ans = True.

Control flow operations

The if operation sets the /ans slot to its second argument if its first argument is True and to its third argument if its first argument is False.

... if True "Hello." "Goodbye." .
ans = "Hello."
... if False "Hello." "Goodbye." .
ans = "Goodbye."

The if operation can be used for control flow by using Expressions. Expressions are created by enclosing statements in {}. The code in an expression is executed when its value is accessed.

... /x 10 .
... if [ gt x 3 ] { print "x is greater than 3." } { print "x is less than three." } .
x is greater than 3.
... /x 1 .
... if [ gt x 3 ] { print "x is greater than 3." } { print "x is less than three." } .
x is less than three.

Expressions are like substatements in that they evaluate to what they set the /ans slot to. Where they differ is that substatements are executed before the main statement is evaluated. Expressions are executed only when they are needed. Expressions are necessary for the if operation to function as a control flow operation. If we wrote the above statements using substatements, all the statements would be evaluated regardless of the truth of the first argument.

... if [ gt x 3 ] [ print "x is greater than 3." . answer 0 . ] [ print "x is less than three." . answer 0 . ] .
x is greater than 3.
x is less than three.
ans = 0

The answer operation sets the /ans slot to a value. To demonstrate the above, I had to add it because otherwise the second and third argument to if would appear to be missing to the code because substatements evaluate to what they set the /ans slot to before the statement processes.

The while operation is a looping operation. It takes two instructions for its argument. It calls the first instruction without any arguments. If the instruction sets the /ans slot to True, it then calls the second instruction without any arguments, and so on. while calls both instructions in the current object so code in the instructions can modify the slots in the current object.

... /i 1 .
... while ( lt-eq i 10 )
  print i .
  incr i .
) .
ans = False.
... print i .

The repeat operation executes an instruction a fixed number of times in the current object. For example, the same loop could have been written as:

... /i 1
... repeat 10 ( print i . incr i . ) .

The repeat loop is faster than the while loop when it is applicable because it does not need to check a condition.


SLOBIL is a prototyped-based object language. New objects can inherit from other objects using the new operation. When changes are made to the parent object, it propogates to all the children. The new operation also adds to (or replaces) the slots included from their parent object in an analogous way to the object operation.

... /+rectangle+ [ object /area ( mul l w ) ] .
... /rect1 [ new +rectangle+ /l 5 /w 4 ] .
... print rect1:/area .
(  mul l w  )
... set /d 2 +rectangle+ .
... set /area ( mul l w d ) +rectangle+ .
... print rect1:/area
(  mul l w d )

The in operation executes code inside a given object. It can be used to do what other languages call "method calls".

... in rect1 rect1:/area .
ans = 40

Without using in, calling rect1:/area will not reference the values at the /l and /w slot in the object at /rect1.

... rect1:/area .
Error: Value at slot /l not found.

Calling instructions within an object is a common thing to do. So SLOBIL provides a convenience syntax. If the first element of a statement is an object, it calls the instruction at the slot provided in the first argument from within the object.

... rect1 /area .
ans = 40

The link between objects created by new is a link between the objects themselves, not the slots at which the objects are inserted. If the parent object is moved, deleted, or the slot is overwritten with a new object, it will not change the children because the object is simply removed from the slot it was located in originally, the object itself has not changed.

... /+rectangle+ [ object /area ( mul w l ) ] .
... /rect1 [ new +rectangle+ /l 5 /w 4 ] .
... rect1 /area .
ans = 20
... move /+rectangle+ /x .
... rect1 /area .
ans = 20
... /+rectangle+ [ object /area ( add l w ) ] .
... rect1 /area .
ans = 20
... delete /x .
... rect1 /area .
ans = 20

Applying Instructions To Data In An Object

The do operation applies an operation to each slot in a set of objects. For example:

... do add [ object /x 2 /y 3 /z 4 ] [ object /x 5 /y 2 ] .
ans = an Object with:
x of type Integer, value: 7
y of type Integer, value: 5

For each slot that has data in all the objects passed to do as arguments, do calls the operation in its first argument using the data from the given slot in each object as positional arguments, in the order the objects are given to do.

do takes operations as arguments, but programmers write instructions, not operations. Instructions can be converted to operations by equipping their code with a fixed set of positional arguments using the op operation.

... do [ op ( div [ sub y x ] x ) /x /y ]
[ object /x 2.0 /y 3.0 /z 4.0 ]
[ object /x 5.0 /y 2.0 ] .
ans = an Object with:
x of type Real, value: 1.500000
y of type Real, value: -0.333333

The op operation converts the instruction given into an operation by setting the slots in the temporary environment in which an instruction is called to the given positional arguments, e.g. in the above, the first argument will be inserted into the slot /x and the second argument to the slot /y.

Objects As Arrays

There is no array type in SLOBIL. Objects are used as array as well. Several operations make use of a slot-naming convention to treat objects like arrays. Slots that match the pattern /name1, /name2, …, /nameN can be treated like an array by operations.

The next operation sets the /ans slot to the next slot given the current slot.

... next /c1 .
ans = /c2

The previous operation sets the /ans slot to the previous slot given the current slot.

... previous /c10 .
ans = /c9

The last operation sets the /ans slot to the last slot in an object that begins with the given prefix.

... /array [ list 1 2 3 ] .
... print array .
an Object with:
t1 of type Integer, value: 1
t2 of type Integer, value: 2
t3 of type Integer, value: 3
... last array /t .
ans = /t3

This example demonstrates the list operation as well which creates a list-like object with data located at slots /t1, /t2, …, /tN.

The collapse operation can be used to summarize a list.

... /array [ list 3 -1 4 ] .
... collapse add array /t .
ans = 6

collapse applies an operation that takes two arguments to each element of the list consecutively. So, in the above example, first add 3 -1 is computed. Then, add ans 4 is computed, and so on.

collapse and last both operate on the /t prefix by default so the last argument can be omitted if that is the prefix desired,

Exceptions and Error Handling

please is the SLOBIL operation for handling errors. It takes two arguments. The first is an instruction to execute in the current object. The second is an instruction to execute if the first instruction fails.

Note that errors will still be printed to the console unless you run interpreter /print-errors False . first.

Saving and Loading Objects

Objects can be saved with the save operation. save saves the current object to the given filepath.

... /test [ object /x 1 /y "hello" /z True ] .
... in test ( save "test.dslob" ) .

The build operation saves objects in a standard location, ~/.dslobs.

... build "test" test .

The above statement saves the object test to ~/.dslobs/test.dslob.

Similarly, the load operation loads a given filepath into the current object, while the use operation imports an object from the standard location for save files, ~/.dslobs.

... load "test.dslob" .
... use "test" .

REPL Settings

The REPL itself has a few settings that can be configured using the interpreter operation. The below example demonstrates how to change the various values from their defaults.

... interpreter /print-ans True .
... interpreter /auto-rehash False .
... interpreter /print-errors False .

The print-ans setting indicates whether to print what the /ans slot is after running each command. The default is not to do so.

The auto-rehash setting indicates whether objects — which, internally, are hash tables — should be automatically rehashed as they grow in size or whether the rehash operation should be used explicitly. The default is to rehash automatically.

The print-errors setting indicates whether to print the trace of the error out when an error is encountered. The default is to do so.

Chaining operations

SLOBIL has an operation called infix (alias: $) that can be used to simulate infix notation when it is convenient. It expects arguments with the pattern DATA OPERATION DATA OPERATION DATA .... It runs the operations on the first two data objects and then uses the result stored in the /ans slot for the first argument and takes the next data element as the second argument and applies the next operation to the two. It is primarily useful for arithmetic that is easier to read in this format.

... add 1 [ sub 3 2 ] .
ans = 2
... + 1 [ - 3 2 ] .
ans = 2
... infix 1 + 3 - 2 .
ans = 2
... $ 1 + 3 - 2 .
ans = 2
... add 1 [ mul 3 2 ] .
ans = 7
... + 1 [ * 3 2 ] .
ans = 7
... $ 1 + [ $ 3 * 2 ] .
ans = 7
... $ 1 + 3 * 2 .
ans = 8

The last line illustrates a limitation of this convenience syntax. It has no notion of precedence. It simply changes the order in which the operations and data are interpreted.

Infix-notation is not very SLOBIL-like so it should be used sparingly, but it is occasionally useful for arithmetic expressions that otherwise might look overly complex.

Multi-threaded Programs

Tasks model processes. They enable multi-threaded programming.

The task operation creates a task. The task operation takes three arguments. The first gives the slot to assign the Task to. The second gives the body of the Task, an instruction that the Task will execute when it is run (Tasks do not immediately start running on creation). The third argument is the initial state of the task, a object defining the environment in which the task will run.

... task /my-task ( commands to run... ) [ object . ] .

The run-task operation starts a task. It takes a single argument, the task to start running. Running a task means that the instruction that forms the body of the task is executed. Only one instance of the task can be running at a given time but the same task can be executed multiple times. The state of the task will not revert to its original state when it is run again.

The structure of a task is described in the below table:

Element Description
Body The instruction run in a separate thread from the main SLOBIL thread.
State A Object that contains the current state of the task. The object being modified by the Task's body.
Queue A Object that contains data queued to pass from the main thread to the Task's thread or vice-versa.

A Task's state object is entirely separate from the current object. There is no way to directly access data in a task except in the body of the task. No data in the Task's queue can be accessed directly in any thread. Data can be sent between the main thread and the task thread using operations.

Tasks accept data when they take data from their queue and move it into their state object. They can do this with one of three operations: accept, accept-or, and select.

The accept operation takes a slot as an argument and waits for data to be available at that slot in the Task's queue. A Task can be provided as an optional second argument to accept to look for the data in another task's queue. Once that data is available, it sets the /ans slot in the Task's state object to the value of the data. accept is blocking so no other code will be executed in the thread running the accept operation until the data is available in the queue. SLOBIL does not allow running accept in the main task because there is no way to exit the blocking. accept-or can be used instead.

The queue operation moves data from one object into the queue of another Task. Its arguments are a slot to set in the queue object, the data to send, and the task's queue to access.

... task /t1 ( print [ accept /hello ] . ) .
... run-task t1 .
... queue /hello "Hi!" t1 .

Because the accept operation blocks the thread until the data is entered into the queue, it cannot be used when the data accept is looking for is optional.

The accept-or operation checks whether data exists at a certain slot in the queue, if it does, it sets the /ans slot to the result. If not, it executes its second argument, an instruction, in its state object. This operation does not block. It checks once if the data is available and otherwise executes the instruction. For example, in a Task body, we might have:

accept-or /hello ( set /hello "Hello." ) .

The main use of accept-or is to provide default values for missing data or to do something else if data is not available.

Alternatively, the select operation executes one of several instructions if data comes in at any number of slots. select takes paired slots and instructions as its arguments. It waits for data to appear in its queue at any of the slots listed. The first slot to receive data is "selected". The instruction associated with the slot is executed in the slot's state object after setting the /ans slot to the value of the data located at the slot in the queue.

... task /t1 ( 
      set /continue True .
      while ( answer continue )
              select /add-one ( print [ add ans 1 ] ) 
                     /sub-one ( print [ sub ans 1 ] )
                     /continue ( set /continue ans ) .
            ) .
    ) .
... run-task t1 .
... queue /add-one 3 t1 .
  ... queue /sub-one 3 t1 .

3. Example Programs

Accounting System

SLOBIL programs can use SLOBIL itself as their means of interacting with the user because the language is "command-like". This section describes a simple double-entry accounting program written in SLOBIL.

Interactive programs are usually created as objects so they can be easily loaded into SLOBIL with both state variables and instructions. So we start by defining the program object which will contain a list of accounts.

  [ object
      /account-list [ object ]
  ] .

Next, we define a generic account object and add it to accounting. I use +name+ as a naming convention for base objects that will be used as prototypes for subsequent objects.

[ object
      last entries /entry .
      next ans .
      set ans entry entries .

      incr balance entry:/amount .
      print [ combine name ": " balance ] .
      print [ combine
                entry:/desc ": "
                  to-string entry:/amount
            ] .
      do [ op print-entry /entry ]
         entries ...
accounting .

To suppress printing out the /ans slot, you can end a statement with three periods ....

Now, we need an instruction for creating a new account. We will have the user specify the account as a slot.

  set name
        new +account+ /name [ to-string name ] /balance balance
            /entries [ object ] 
      ] account-list .
accounting .

This instruction might not seem to do much beyond what the new operation does. One advantage of defining this instruction is that it will give an intelligible error if the user does not specify a name for the account and an opening balance. The new operation doesn't expect any particular slots to be set, but the new-account instruction does.

We next need an instruction to transfer money between two accounts. Let's define one.

    /to-entry [ object /desc desc /amount amount ] .
    /from-entry [ object /desc desc /amount [ mul -1 amount ] ] .

    if [ exist from-account account-list ]
         account-list:from-account /add-entry /entry from-entry .
         if [ exist to-account account-list ]
              account-list:to-account /add-entry /entry to-entry .
            } .
       } .
  accounting .

Lastly, let's add some instructions to summarize our accounts and print out entries in a given account.

    do [ op ( account /summary ) /account  ]
       account-list ...
  accounting .

    account-list:account /print-entries .
  accounting .

Let's see the program in action.

  ... accounting /new-account /name /Checking /balance 1000.50 .
  ... accounting /new-account /name /Savings /balance 20000.00 .
  ... accounting /transfer
  /desc "Saving Money"
  /amount 100
  /to-account /Savings
  /from-account /Checking .
...  accounting /summary .
Savings: 20100.000000
Checking: 900.500000
... accounting /entries /account /Checking .
Saving Money: -100

The user shouldn't have to type accounting every time. Temporarily, in the session, we can import it, but to package it for users, it is better to use the build operation to save the object to disk.

... build "accounting" accounting .

Now, whenever we start a SLOBIL session, we can simply type:

... use "accounting" .
... new-account /name /Checking /balance 1000.50 .
... summary .

A Time-Keeping Program

I used this program to keep track of billable hours for about three years. It is certainly the most used SLOBIL program as of June 2023.

' Initial state

/current-thing "Nothing" .
/last-clock -1 .
/record [ object ] .
/running False .
/current-file Nothing .

' Start a new record of work or load an old one

  [ op (
            up set /current-file file .
            please ( load file record )
                     up set /record [ object ] .
                     up set /thing-list [ object ] record .
                     print "Starting new file." .
                   ) .
      ) /file
  ] .

' Save record of work in SLOBIL format
    in record ( save current-file ) .
  ) .

' Set current thing
  [ op
        if [ not running ]
             if [ exist /name ]
                  up set /current-thing name .
                  add-thing-to-list name .
                  up set /current-thing [ choose-thing ] .
                } .
             up set /last-clock -1 .
             print "Currently running, stop first." .
           } .
      /name ] .

' Start clock for current thing
    if [ not running ]
         up set /last-clock [ clock ] .
         up set /running True .
         print [ combine "Starting on " current-thing " ..." ] .
         print "Currently running, stop first." .
       } .
  ) .

' Stop clock for current thing with a description of task.
    if running
         last record /r .
         next ans .
         set ans
                 /thing current-thing
                 /start-time last-clock
                 /stop-time [ clock ]
                 /description desc
             record .
         up set /running False .
         save-hours .
         print "Not currently running." .
       } .
  ) .

' A map to day of week
  ] .

' Convert to hours
  [ op
        do [ op ( div t 1000.0 60 60 ) /t ] structure .
      /structure ] .

' Return a structure describing a single day of activity
  [ op
        /final [ object ] .
                  /day day
                  /month month
                  /year year
                  /hour 0
                  /minute 0
                  /seconds 0
                  /milliseconds 0
          ] .

                  /day day
                  /month month
                  /year year
                  /hour 23
                  /minute 59
                  /seconds 59
                  /milliseconds 999
          ] .

        /i /r1 .
        while ( exist i record )
                if [ and
                       [ gt-eq record:i:/start-time clock1 ]
                       [ lt-eq record:i:/start-time clock2 ] ]
                     /thing [ to-slot record:i:/thing ] .
                     /elapsed [ sub record:i:/stop-time
                                    record:i:/start-time ] .

                     if [ exist thing final ]
                          set thing [ add final:thing elapsed ]
                              final .
                          set thing elapsed final .
                        } .
                   } .
                /i [ next i ] .
              ) .

        make-hours-day-time final .
      ) /year /month /day ] .

' Add thing to thing list
  [ op (
        if [ not [ exist /thing-list record ] ]
             set /thing-list [ object ] record .
           } .
        last record:/thing-list /c .
        next ans .
        set ans thing record:/thing-list .
       /thing ] .

' Select thing from menu
    /i /c1 .
    while ( exist i record:/thing-list )
                  [ to-string [ to-number i ] ]
                  ": " 
              ] .
            /i [ next i ] .
          ) .
    print "Choose Thing: " False .
    input /num .
    /loc [ to-slot [ combine "c" num ] ] .
    answer record:/thing-list:loc .
  ) .

' Print status
    print [ combine "Current thing: " current-thing ] .
    if running
         print "Running a task." .
         print "Not running." .
       } .
  ) .

' Update thing in list
    /i /c1 .
    /cont True .
    while ( and
              [ exist i record:/thing-list ]
              cont )
            if [ string-eq record:/thing-list:i thing ]
                 set i new-thing record:/thing-list .
                 /cont False .
               } .

            /i [ next i ] .
          ) .

    ' Update thing in records

    /i /r1 .
    while ( exist i record )
            if [ string-eq record:i:/thing thing ]
                 /thing new-thing record:i .
               } .
            /i [ next i ] .
          ) .
  ) .

' Rewind X minutes from start
  [ op
        if [ not running ]
             print "Currently not running." .
             up set /last-clock [ sub last-clock [ mul x 60 1000 ] ] .
           } .
      ) /x ] .

' Rewind X minutes from last entry
  [ op (
        if running
             print "Currently running." .
             /end [ last record /r ] .
                 sub record:end:/stop-time [ mul x 60 1000 ]
               record:end .
           } .
      ) /x ] .

4. Example Instructions


set /swap
      set /tmp input:i .
      set i input:j input .
      set j tmp input .
    ) .

set /partition
      set /pivot input:end .
      set /i start .
      set /j start .
      set /cont True .
      while ( answer cont )
              if [ compare input:j pivot ]
                   swap /input input /i i /j j .
                   set /i [ next i ] .
                 } .

              if [ slot-eq j end ]
                   set /cont False .
                 } .

              set /j [ next j ] .
            ) .

      swap /input input /i i /j end .
      answer i .
    ) .

set /-quicksort
      if [ not [ slot-eq start end ] ]
           partition /input input /start start /end end /compare compare . 
           move /ans /p .
           if [ not [ slot-eq p start ] ]
                -quicksort /input input /start start /end [ previous p . ] .
              } .

           if [ not [ slot-eq p end ] ]
                -quicksort /input input /start [ next p . ] /end end .
              } .
         } .
    ) .

set /quicksort
      if [ not [ exist /end ] ]
           set /end [ last input slice . ] .
         } .
      if [ not [ exist /start ] ]
           set /start [ next slice . ] . 
         } .

      if [ not [ exist start input ] ]
           error "Starting slot not found in input." .
         } .

      if [ not [ exist end input ] ]
           error "Ending slot not found in input." .
         } .

      -quicksort /input input /start start /end end /compare compare .
    ) .

Example of use:

... set /x [ list 3 2 4 1 ] .
... quicksort /input x /slice /t /compare lt .
... print x .
ans = a object with:
t1 of type Integer, value: 1
t2 of type Integer, value: 2
t3 of type Integer, value: 3
t4 of type Integer, value: 4
... quicksort /input x /slice /t /compare gt .
... print x .
a object with:
t1 of type Integer, value: 4
t2 of type Integer, value: 3
t3 of type Integer, value: 2
t4 of type Integer, value: 1

A Line-Oriented Text Editor

This example is a simple interactive program where the user enters commands to edit a buffer.

' Line-oriented text editor
/slobed [ object . ] .
in slobed
     /buffer [ list . ] . 
     /cur-line /t1 . 
     /n ( up set /cur-line [ next cur-line . ] . ) .
     /p ( up set /cur-line [ previous cur-line . ] . ) .
       [ op (
         /arbed-str s buffer .
         in buffer
              set cur-line arbed-str .
            ) .
       /s ] . 
         print [ get cur-line buffer . ] .
       ) .
   ) .

Example of use:

... import slobed .
... i "Hello" .
... o .
... n .
... i "Goodbye" .
... o .
... p .
... o .

Numerical Differentiation

' Compute the numerical derivative of an operation that takes an arg
set /deriv
      if [ not [ exist /h ] ]
           set /h 0.001 .
         } .
      div [ sub [ f [ add x h ] ]
                [ f [ sub x h ] ] ]
          [ mul 2 h ] .
    ) .

Example of use:

... set /f [ op ( power t 2 ) /t ] .
... deriv /f f /x 1.0
ans = 2.0

Compute Factorial

' compute a factorial using while
set /factorial
    [ op (
      /i 2 .
      /prod 1 .
      while ( lt-eq i t )
              /prod [ mul i prod ] .
              incr i .
            ) .
      answer prod .
    ) /t ] .

' compute factorial using recursion

set /-factorial-recurse
      if [ eq t 1 ]
           mul t [ -factorial-recurse /t [ sub t 1 ] ] .
         } .
    ) .

set /factorial-recurse [ op -factorial-recurse /t ] .

Example of use:

... factorial 5 .
ans = 120
... factorial-recurse /t 5 .
ans = 120

Note on Recursion

Operations cannot be directly defined recursively, but Instructions can be. That is why the code above first defines -factorial-recurse as an instruction and then creates the operation.

Numerical Integration

' takes an operation as an argument and return left hand
' riemmann sum over range

set /integrate 
      /delta [ div [ sub ub lb ] n ] .
      /x lb .
      /int 0.0 .
      repeat n
               incr int [ f x ] .
               incr x delta .
             ) .
      mul int delta .
    ) .

Example of use:

... integrate /f [ op ( power t 2 ) /t ] /lb 0.0 /ub 1.0 /n 1000 .
ans = 0.332834

Basic Linear Algebra

This example demonstrates both application methods like do and collapse as well as when to use operations for programmer code. Operations make more sense when the arguments are all the same kind of thing, the order is the only thing that might matter, like in this example where we are multiplying two matrices. Instructions are preferred when the argument's position is uninformative about the purpose of the argument, as in the previous example with numerical integration.

' Computes v^T w for a vector 
set /dotproduct
    [ op (
      do mul v w .
      collapse add ans  .
    ) /v /w ] .

' matrix-multiply A B computes A^T B
set /matrix-multiply
    [ op (
      set /i /t1 .
      set /out [ list ] .
      while ( exist i B )
              do [ op ( dotproduct t1 B:i ) /t1 ] A .
              in out ( set i ans ) .
              next i .
              move /ans /i .
            ) .
      answer out .
    ) /A /B ] .

' Computes A^T 
set /transpose
    [ op (
      set /i /t1 .
      set /out [ list ] .
      while ( exist i A:/t1 )
              do [ op ( answer t1:i ) /t1 ] A .
              move /ans /res .
              in out ( set i res ) .
              next i .
              move /ans /i .
            ) .
      answer out .
    ) /A ] .

Example of use:

... set /A [ list [ list 1 2 ] [ list 3 4 ] ] .
... set /B [ list [ list 6 2 ] [ list 3 4 ] ] .
... transpose A .
ans = a object with:
t1 of type Object, value: a object with:
t1 of type Integer, value: 1
t2 of type Integer, value: 3
t2 of type Object, value: a object with:
t1 of type Integer, value: 2
t2 of type Integer, value: 4
... matrix-multiply A B .
ans = a object with:
t1 of type Object, value: a object with:
t1 of type Integer, value: 10
t2 of type Integer, value: 26
t2 of type Object, value: a object with:
t1 of type Integer, value: 11
t2 of type Integer, value: 25

Split a String

' Tokenize a string /line by splitting on string /sep
set /tokenize
      set /i 1 .
      set /len [ length line . ] .
      set /cur-reg /t1 .
      set /tokened [ list . ] .
      set /init True .
      while ( lt-eq i len . )
              set /d [ substring line i i . ] .
              if [ string-eq d sep . ]
                   in tokened ( set cur-reg buffer . ) .
                   set /cur-reg [ next cur-reg . ] .
                   set /init True .
                   if init
                      { set /buffer d . set /init False . }
                      { set /buffer [ combine buffer d . ] . } .
                 } .
              set /i [ add i 1 . ] .
            ) .
      in tokened ( set cur-reg buffer . ) .
      answer tokened .
    )  .

Examples of use:

... tokenize /line "1,2,3" /sep "," .
ans = a object with:
t1 of type String, value: 1
t2 of type String, value: 2
t3 of type String, value: 3

Concurrent Programming

SLOBIL uses Tasks to run Instructions in separate processes. The following example demonstrates how queue, accept, and select work to move data between the main Task and other Tasks.

' Demonstrate tasks

task /t1
       while ( answer True . )
               queue /current [ accept /hello . ] .
             ) .
     [ object . ] .

run-task t1 .

queue /hello "Hi!" t1 .
accept-or /current ( print "Result not ready yet." . ) t1 .

task /t2
       set /continue True .
       while ( answer continue . )
                   print [ mul ans 2 . ] .
                   print [ mul ans 3 . ] .
                   set /continue False .
                 ) .
             ) .
     [ object . ] .

run-task t2 .
queue /double 3 t2 .
queue /triple 10 t2 .
queue /double 7 t2 .
queue /end Nothing t2 .

The following task that can be used to run any code in the background.

task /t1
       /instr [ accept /instruction ] .
       print "HELLO" .
       accept /context .
       import ans .
       instr .
       queue /result ans .
     [ object ] .

run-task t1 .
queue /instruction ( add x y ) t1 .
queue /context [ object /x 2 /y 4 ] t1 .
accept-or /result ( print "Result not ready yet." ) t1 .
accept-or /result ( print "Result not ready yet." ) t1 .

Linking C code

One of the big outstanding tasks with SLOBIL is to write a more user-friendly (and documented) libslobil for adding extensions, but it is currently possible to write SLOBIL operations in C, using SLOBIL's link operation to import the code.

The following is an example of C code.

   A C Function to compute log(x+1) 

/* Change to wherever slobil.h is located or just "slobil.h" if it is on the path */
#include "../src/slobil.h"
#include <math.h>

log_plus_one (arg a, object* reg)

  check_length(&a, 2, "log1", reg->task->task);
  if (is_error(-1, reg->task->task)) return;

  data* arg1 = resolve(a.arg_array[1], reg);

  if (arg1 == NULL)
      do_error("<log1> requires an argument.", reg->task->task);

  if (arg1->type != Integer && arg1->type != Real)
      do_error("Argument to <log1> must be numeric.", reg->task->task);

  double ans;
  if (arg1->type == Integer)
      double z = mpz_get_d(*((mpz_t*) arg1->data));
      ans = log(z + 1.0);
      ans = log(*((double*) arg1->data) + 1.0);

  data* d;
  assign_real(&d, ans);

We then compile it into a shared object file, linking against libslobil.


## Assumes you have already make installed briple so that libbriple is on your path and that the
## library is installed in /usr/local/lib.  Modify path if installed elsewhere.

gcc -c -fPIC -o link.o link.c
gcc -shared -Wl,-rpath -Wl,/usr/local/lib -o link.o -lslobil

The code then can be loaded into SLOBIL with the link operation like so:

' Demonstrates linking C code in
link "./" "log_plus_one" "log1" .

The first argument of link gives the shared-object file name. The second argument gives the name of the function. The third argument gives what the name of the SLOBIL operation will be.

Now, the operation can be called in the following way:

... log1 1 .
ans = 0.693147

5. Reference

This section gives the full vocabulary of the language. The grammar of the language is described in the previous sections. I describe each type of data, and the operations associated with it.

Throughout, I enclose an operation's optional arguments between bars (||).


Short description

A object contains data located at slots. Data can be retrieved from and inserted into objects. Objects also defined the scope of SLOBIL code because code is executed inside objects. So the values of variables depend on which object you are executing the code. This allows the user to flexibly manipulate scope.

Implementation details

Objects are hash tables. The keys to the table are called slots. The number of bins in the hash table grows as more elements are added. This keeps lookup times low, but the object will rehash as it grows. Rehashing can be turned off by using the auto-rehash operation.

Object operations

  • Creation
    • object

      Usage: object SLOT1 VALUE1 SLOT2 VALUE2 ...

      Sets the /ans slot to a object with VALUE1 located at SLOT1 and so on.

    • list

      Usage: list VALUE1 VALUE2 ...

      Set the /ans slot to a Object with VALUE1 at Slot /t1, VALUE2 at Slot /t2, and so on.

    • range

      Usage: range INTEGER1 INTEGER2 |INTEGER3|

      Set the /ans slot to a Object with INTEGER1 at /t1 and INTEGER1 + INTEGER3 at /t2 and so on so long as the value is less than or equal to INTEGER2.

  • Insert, move, and remove data to and from slots
    • set

      Usage: set SLOT VALUE |OBJECT|

      Sets the value at SLOT to VALUE in the object OBJECT. If the OBJECT argument is omitted, then it will set the slot in the current object.

    • move

      Usage: move SLOT1 SLOT2

      Move the value located at SLOT1 to SLOT2. Does not copy the data so it is an efficient way to move data.

    • delete

      Usage: delete SLOT

      Delete the value at SLOT in the current object.

  • Access data in Object
    • get

      Usage: get SLOT |OBJECT|

      Sets the /ans slot to the value located at SLOT in OBJECT. If the OBJECT argument is not specified, get from the current object.

    • exist

      Usage: exist SLOT |OBJECT|

      Set the /ans slot to True if a value exists at the SLOT in OBJECT. If the OBJECT argument is omitted, check in the current object.

    • import

      Usage: import OBJECT

      Set the Slots in the current Object to hold the same values that they hold in OBJECT.

    • filter

      Usage: filter OBJECT OPERATION

      Set the /ans slot to a Object containing all the elements in OBJECT such that the OPERATION applied to the element of the Object sets the /ans slot to True.

  • Apply Operations to elements of a Object
    • do


      Execute OPERATION which takes its arguments (1…N) from each element in OBJECT1, …, OBJECTN. Sets the /ans slot to a Object which contains whatever the OPERATION evaluates to at the corresponding Slots. For example, do add [ list 1 2 3 . ] [ list 4 5 6 . ] sets the /ans slot to a Object with elements (5,7,9) at slots (/t1,/t2,/t3). do will only return results at Slots that exist in all Objects. So, for example, do add [ list 1 2 3 . ] [ list 4 5 . ] sets the /ans Slot to list 5 7.

    • collapse

      Usage: collapse OPERATION OBJECT |SLOT|

      Sets the /ans slot to the value of applying OPERATION to the value in the OBJECT at Slot /SLOT1 and /SLOT2 and then again to the result of that and to the value of /SLOT3 and so on. For example, collapse add [ list 1 2 3 . ] /t sets the /ans slot to 6. If the SLOT argument is omitted, it is assumed to be /t.

  • Execute code in a object
    • in



    • up

      Usage: up STATEMENT

      Execute STATEMENT in the object above the current one after resolving the values of the arguments of the statement in the current object. For example, we can create an Instruction that can be used to increment a variable in place, like so:

      ... set /inc ( up set x [ add 1 [ up get x . ] . ] . ) .
      ... set /x 1 . 
      ... inc /x /x . 
      ... print x .
  • Test if a object
    • is-object

      Usage: is-object VALUE

      Sets the /ans Slot to True if VALUE is a Object and to False otherwise.

  • Technical
    • rehash

      Usage: rehash OBJECT

      Manually rehash the object's underlying hash table.

Reals and Integers

Short description

Real and Integer are distinct types in SLOBIL. A Real is a number with a decimal point. An Integer is a number without a decimal point. Sometimes either type can be used for an operation. In this case, I refer to the argument type as a Number in describing the operation for brevity. Number is not a SLOBIL type.

Implementation details

A Real is a double-precision floating point value (equivalent to C's double).

An Integer is an arbitrarily long integer (a "bignum"). Integers are implemented using GnuMP.

Real and Integer operations

  • Arithmetic operations
    • add

      Usage: add NUMBER1 NUMBER2 ...

      Adds all the numbers together and sets the /ans slot to the result.

    • mul

      Usage: mul NUMBER1 NUMBER2 ...

      Multiplies all the numbers together and sets the /ans slot to the result.

    • sub

      Usage: sub NUMBER1 NUMBER2 ...

      Subtracts the second number from the first and the third number from that and so on and sets the /ans slot to the result.

    • div

      Usage: div NUMBER1 NUMBER2 ...

      Divides the first number by the second, the result by the third number, and so on and sets the /ans slot to the result.

    • mod

      Usage: mod NUMBER1 NUMBER2

      Return the remainder of dividing the first number by the second.

    • incr

      Usage: incr INTEGER1 |INTEGER2|

      Increment INTEGER1 by INTEGER2 or by 1 if INTEGER2 is omitted. The difference between this operation and add is that it modifies INTEGER1 in place. INTEGER2 can be a negative number.

  • Comparison operations
    • gt

      Usage: gt NUMBER1 NUMBER2

      Set the /ans slot to True if NUMBER1 is greater than NUMBER2 and to False otherwise.

    • lt

      Usage: lt NUMBER1 NUMBER2

      Set the /ans slot to True if NUMBER1 is less than NUMBER2 and to False otherwise.

    • eq

      Usage: eq NUMBER1 NUMBER2

      Set the /ans slot to True if NUMBER1 is equal to NUMBER2 and to False otherwise.

    • lt-eq

      Usage: lt-eq NUMBER1 NUMBER2 — set the /ans slot to True if NUMBER1 is less than or equal to NUMBER2 and to False otherwise.

    • gt-eq

      Usage: gt-eq NUMBER1 NUMBER2

      Set the /ans slot to True if NUMBER1 is greater than or equal to NUMBER2 and to False otherwise.

  • Conversion operations
    • to-number

      Usage: to-number STRING|SLOT

      If the argument is a String, try to convert to a number and set the /ans Slot to the result. If the argument is a Slot and ends in a number, set the /ans Slot to the result.

    • to-real

      Usage: to-real INTEGER

      Set the /ans Slot to a Real representing the INTEGER.

  • Test if type operations
    • is-integer

      Usage: is-integer VALUE

      Sets the /ans Slot to True if the Value is an Integer and to False otherwise.

    • is-real

      Usage: is-real VALUE

      Sets the /ans Slot to True if the Value is a Real and to False otherwise.

  • Common mathematical operations
    • log

      Usage: log NUMBER

      Set the /ans Slot to the natural logarithm of NUMBER.

    • exp

      Usage: exp NUMBER

      Set the /ans Slot to the NUMBER power of the natural base.

    • power

      Usage: power NUMBER1 NUMBER2

      Set the /ans Slot to NUMBER1 raised to the NUMBER2 power.

    • floor

      Usage: floor REAL1

      Set the /ans Slot to the greatest Integer less than REAL1.

    • ceiling

      Usage: ceiling REAL1

      Set the /ans Slot to smallest Integer greater than REAL1.


Short description

Strings in SLOBIL are text. A string literal is enclosed in quotation marks. SLOBIL supports UTF-8 encodings. Non-ASCII characters are handled correctly: a single character is a single character no matter how many bytes it is. It also implements a collection of escape sequences for whitespace and quotation marks that should be included in the string itself.

The escape sequences are:

Escape Sequence Meaning
\\ \
\' ' (single-quote)
\t tab
\n newline
\r carriage return
' (single-quote) " (double quote)

Implementation details

Strings are internally UTF-32 encoded to enable faster access by index number and because it makes creating substrings faster. SLOBIL accepts UTF-8 as input because that is more common in terminals and in file-encodings.

String operations

  • Access, search, and modify string elements
    • substring

      Usage: substring STRING INTEGER1 INTEGER2

      Sets the /ans Slot to the subset of STRING where the characters included are determined by INTEGER1 and INTEGER2. Strings are 1-indexed in SLOBIL so the first character is at location 1. If the INTEGER is less than or equal to 0, determine the location from the end of the String. So if INTEGER1 and INTEGER2 are 0, then it will set the /ans slot to the last character in STRING.

    • match

      Usage: match STRING1 STRING2 |INTEGER|

      Find occurences of regular expression STRING1 in String STRING2. Sets the /ans Slot to a Object with all submatches located at the /tN objects. The optional third argument gives the number of matches to return. If 0 is provided, return all matches (default).

    • replace

      Usage: replace STRING1 STRING2 STRING3 |INTEGER|

      Set the /ans Slot to a String formed by replacing all occurences of regular expression STRING1 with STRING2 in STRING3. The optional fourth argument gives the number of matches to replace. If 0, replace all (default).

  • String properties
    • length

      Usage: length STRING

      Sets the /ans slot to the number of characters in STRING.

  • String comparison
    • string-eq

      Usage: string-eq STRING1 STRING2

      Sets the /ans Slot to True if the two strings are equal and to False otherwise.

    • string-lt

      Usage: string-lt STRING1 STRING2

      Sets the /ans Slot to True if STRING1 is less than STRING2 in the sense that the ASCII characters have lower values.

    • string-gt

      Usage: string-gt STRING1 STRING2

      Sets the /ans Slot to True if STRING1 is greater than STRING2 in the sense that the ASCII characters have lower values.

    • char-eq

      Usage: char-eq STRING1 INTEGER STRING2

      Test if character INTEGER of string (using same index numbers as for substring) is equal to STRING2. This is a slight performance improvement over testing whether the substring with only one character is equal to the string.

  • Combine strings
    • combine

      Usage: combine STRING1 STRING2 ... STRINGN

      Sets the /ans slot to the concatenation of the two Strings so that the resulting String is "STRING1STRING2".

  • Convert to string
    • to-string

      Usage: to-string INTEGER|REAL|SLOT |INTEGER2|

      Sets the /ans Slot to a String representing the INTEGER or REAL or SLOT provided as the first argument. The second argument is used if a REAL argument is provided. INTEGER2 gives the number of elements after the decimal point to include. If not provided, 6 decimal places are included.

  • Test if string
    • is-string

      Usage: is-string VALUE

      Sets the /ans Slot to True if the VALUE is a String and to False otherwise.

  • Strings from User Input
    • input

      Usage: input SLOT

      Reads a line of text the user enters and sets SLOT to that value (always a String).


Short description

Slots are a type of data in SLOBIL usually used to refer to locations in slots. More generally, they are symbols. They can be compared with one another and modified. Slots are not "associated" with objects. They are data without any associated context.

Implementation details

Slots are a structure containing the name of the object and the hashed value of the name so they can be easily inserted into the object hash table.

Slot operations

  • Operations on "list" slots
    • next

      Usage: next SLOT

      If the SLOT ends in a number, return the Slot with that number incremented by 1.

    • previous

      Usage: previous SLOT

      If the SLOT ends in a number, return the Slot with that number minus 1. If that would cause the number to be less than 1 set the /ans Slot to the "first" slot with that prefix so that previous /t1 . sets /ans to /t1.

    • last

      Usage: last OBJECT SLOT

      Return the last Slot in the OBJECT that starts with SLOT. So that if you had slots /x0, /x1, and /x2 in the Object, last OBJECT /x would return /x2.

  • Convert to slot
    • to-slot

      Usage: to-slot STRING|INTEGER

      Sets the /ans slot to a Slot named STRING or to /tINTEGER.

  • Slot comparison
    • slot-eq

      Usage: slot-eq SLOT1 SLOT2

      Sets the /ans Slot to True if the two Slots are the same and to False otherwise.

  • Test if a slot
    • is-slot

      Usage: is-slot VALUE

      Sets the /ans Slot to True if the VALUE is a Slot and to False otherwise.


Short description

Booleans can take on two values: True or False. Comparison and testing operations usually set the /ans slot to a Boolean value.

Implementation details

Booleans are simply a binary value. They use the C99 bool type internally.

Boolean operations

  • is-boolean

    Usage: is-boolean VALUE

    Sets the /ans Slot to True if the VALUE is a Boolean and to False otherwise.

  • and

    Usage: and BOOLEAN1 BOOLEAN2

    Sets the /ans Slot to True if BOOLEAN1 and BOOLEAN2 are True and to False otherwise.

  • or

    Usage: or BOOLEAN1 BOOLEAN2

    Sets the /ans Slot to True if either BOOLEAN1 or BOOLEAN2 are True and to False otherwise.

  • not

    Usage: not BOOLEAN

    Sets the /ans Slot to True if BOOLEAN is False and to False otherwise.


Short description

Instructions are code objects which have not yet been executed. They can be called or executed in different objects.

Implementation details

Instructions are internally "compiled" code. They are then supplied with an environment (a object) before they are executed. The compiled code object is a linked list of statements each of which is a linked list of elements. Elements are either literal data values or the names of slots to lookup in the environment.

Instruction operations

  • call


    Executes INSTRUCTION in a Object with SLOT1 assigned to VALUE1 and so on.

  • is-instruction

    Usage: is-instruction VALUE

    Sets the /ans Slot to True if the VALUE is an Instruction and to False otherwise.

  • op


    Set the /ans slot to an operation that calls INSTRUCTION after binding SLOT1 to the first argument, and so on.

  • code

    Usage: code INSTRUCTION

    Sets the /ans slot to a String containing the code for the INSTRUCTION.

  • is-operation

    Usage: is-operation VALUE

    Sets the /ans Slot to True if the VALUE is an Operation and to False otherwise.

  • set-help

    Usage: set-help INSTRUCTION STRING

    Sets the help for INSTRUCTION to STRING.

  • help

    Usage: help INSTRUCTION

    Print the help string.

  • bind


    Modifies the environment the instruction executes in so that INSTRUCTION now has slot values fixed to the SLOT VALUE pairs. For example, suppose we have an instruction sum defined as ( add t s ). Then, after bind sum /t 2, /sum /s 3 will set the /ans slot 5.


Short description

Files are stream objects that you can write to and read from.

Implementation details

Files are like the C FILE type.

File operations

  • is-file

    Usage: is-file VALUE

    Sets the /ans Slot to True if the VALUE is a File and to False otherwise.

  • open-file

    Usage: open-file STRING1 |STRING2|

    Sets the /ans Slot to a File object corresponding to the file named STRING1 with mode STRING2 (default: "r+").

  • read

    Usage: read FILE

    Read a byte from a file and set the /ans slot to the result (an Integer).

  • read-char

    Usage: read-char FILE

    Read a single character from a File object and set the /ans Slot to that character (a String).

  • read-line

    Usage: read-line FILE

    Sets the /ans Slot to the next line from FILE.

  • write

    Usage: write INTEGER FILE

    Integer must be in [0,255]. Directly writes a byte to FILE.

  • write-string

    Usage: write-string STRING FILE

    Write a STRING to FILE using UTF-8 encoding.

  • close

    Usage: close SLOT

    If a File object is located at SLOT, close the File and remove its reference from the SLOT.


Short description

Nothing is a value that is not any other value and is a different type than any other value.

Nothing operations

  • is-nothing

    Usage: is-nothing VALUE

    Sets the /ans slot to True if the value is Nothing and to False otherwise.

Task Operations

Short description

Tasks are objects that allow you to execute code in another thread and share data between threads.

Implementation details

Tasks contain three elements:

  1. A Body, an instruction that is executed when the Task is run.
  2. A State, a object that contains the state of the Task. The Body is run inside the State object. It is persistent across Task runs.
  3. A Queue, a object that cannot be reached directly but which facilitates data sharing across tasks without worrying about race conditions or other details.

Tasks use mutexes to ensure data is transferred correctly between threads.

Task operations

  • task


    Sets SLOT to contain a new Task with its Body given by the INSTRUCTION and the initial state being set to OBJECT. If no OBJECT argument is given, the initial state is a object containing only the basic operations (the object always contains the basic operations even if they are not in the initial object passed to Task).

  • run-task

    Usage: run-task TASK

    Executes the Task's Body in a separate thread. The same Task object cannot be running in two threads. The operation will give an Error if it is already running.

  • queue

    Usage: queue SLOT DATA |TASK|

    Sets the SLOT in the Queue of TASK to value DATA. If the TASK argument is omitted, it is assumed to be set in the queue of the current task (for sharing Task data with another thread). queue cannot be used for the main SLOBIL Task.

  • accept

    Usage: accept SLOT |TASK|

    Waits until SLOT has a value in TASK's Queue. Once it finds a value, set the /ans slot to that value. If TASK is omitted, wait for the current Task's Queue to be set.

  • select


    Waits for the Queue in the current task to contain data at any of the Slots (it will prefer earlier Slots if data is available at both). Once it receives data, it sets the /ans slot to the data and executes the Instruction in the current object.

  • accept-or

    Usage: accept-or SLOT INSTRUCTION |TASK|

    Checks if SLOT is set in TASK's Queue. If it is, the /ans slot is set to the result. If it is not, it executes INSTRUCTION. If TASK is omitted, search in the current TASK's Queue.

Control flow operations



If the first argument is True, sets the /ans slot to VALUE1, if it is False, sets the /ans slot to VALUE2. If VALUE2 is omitted, do nothing if the first argument is False.



Call INSTRUCTION1 in the current Object. If it sets its /ans slot to True, call INSTRUCTION2. Repeat.






Call INSTRUCTION1. If there is an error, then call INSTRUCTION2.

Environment operations

Modify the /ans slot

  • answer

    Usage: answer VALUE

    Set the /ans slot to VALUE.

  • sit

    Usage: sit

    Do nothing but lookup all arguments (causes Expressions — instructions in curly brackets — to be executed).


  • exit

    Usage: exit

    Exit SLOBIL.

Print output

  • print

    Usage: print VALUE |BOOLEAN|

    Prints VALUE to screen. If BOOLEAN is False, then omit the newline (default: add newline after printing value).

Input and output files and state

  • source

    Usage: source STRING

    Executes SLOBIL code in the file named by STRING.

  • save

    Usage: save FILENAME

    Save the contents of the current object to file.

  • load

    Usage: load FILENAME

    Load the contents of a saved file into the environment.

  • output-code

    Usage: output-code STRING

    Outputs the code that has been entered at the prompt so far to the file named STRING.

  • clear-code

    Usage: clear-code

    Clear code that has been entered so far so that the code that output-code outputs will be empty.

Error handling

  • error

    Usage: error STRING |INTEGER|

    Outputs error message String and sets an error code INTEGER (if specified, otherwise, the error number is 1).

  • is-error

    Usage: is-error INSTRUCTION

    Sets the /ans Slot to True if there was an error executing the INSTRUCTION and to False otherwise.

  • ignore-errors

    Usage: ignore-errors INSTRUCTION

    Ignore any errors while executing the instruction, i.e. go to the next statement if one statement errors.


  • version

    Usage: version

    Sets the /ans Slot to a String giving the version of SLOBIL.

System operations

Interacting with the shell

  • shell

    Usage: shell STRING

    Execute the shell command STRING.

  • change-dir

    Usage: change-dir STRING

    Change directory to the location given in STRING.

  • current-dir

    Usage: current-dir

    Set the /ans Slot to a String giving the current directory.


  • clock

    Usage: clock

    Set the /ans slot to the current time in milliseconds from January 1, 1970.

  • make-time

    Usage: make-time INTEGER

    Given a clock value in milliseconds (as returned by clock) return a object with elements second (a number of seconds between 0-59), minute (giving a number between 0-59), hour (a number between 0-23), day (giving a number between 1-31),

  • make-clock

    Usage: make-clock OBJECT

    Make a clock value in milliseconds from a object describing the time (like the object returned by make-time)

Random numbers

  • rand

    Usage: rand |INTEGER|

    Set the /ans Slot to a uniformly distributed random Real between 0 and 1. If INTEGER is provided, set the seed to the INTEGER before drawing random value.

Package operations


Usage: use STRING

Load a saved object in ~/.dslobs/ with the extension .dslob into the current object. The file being loaded is: ~/.dslobs/STRING.dslob.


Usage: build STRING OBJECT

Saves contents of object to ~/.dslobs/STRING.dslob so that it can be loaded as a package.



Loads shared object file STRING1 and its function named STRING2 into SLOBIL operation named STRING3.

Interpreter options


  • interpreter

    Usage: interpreter SLOT VALUE

    Sets interpreter option SLOT to VALUE.

List of options

  • print-ans

    Usage: /print-ans

    If True, then print the value of the /ans Slot at the end of commands, if False (default) or any other non-Boolean value, suppress printing.

  • auto-rehash

    Usage: /auto-rehash

    If True (default) or any non-Boolean value, then rehash objects automatically as they grow in size. If False do not rehash automatically.

  • print-errors

    Usage: /print-errors

    If True (default) or any non-Boolean value, then print error descriptions. if False, do not print error descriptions.

6. Saved Objects

Note: When saving, only "permanent" data is written to disk. For example, operations written in C will not be written to disk because these are linked in at run time. File values will also not be written to disk because the file stream would need to be re-opened after restarting SLOBIL in any case; it has no permanent information. All other data types are written to disk.

This section will describe the storage format for SLOBIL saved files. A user or programmer will never need to know the internal structure of the save file, but it will be provided here to have complete documentation and to perhaps be useful to people writing a C extension to SLOBIL.

7. GNU Free Documentation License

GNU Free Documentation License

Version 1.3, 3 November 2008

Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. <>

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.


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This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.


This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

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"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

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An MMC is "eligible for relicensing" if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

    Copyright (C)  YEAR  YOUR NAME.
    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.3
    or any later version published by the Free Software Foundation;
    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
    A copy of the license is included in the section entitled "GNU
    Free Documentation License".

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the "with … Texts." line with this:

    with the Invariant Sections being LIST THEIR TITLES, with the
    Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

Author: Zach Flynn

Created: 2023-12-14 Thu 00:59