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JL

This is a small, embeddable LISP-like language. The intended use is for configuration files where it is desirable to be able to have complex configurations (JWM, for example).

This is still a work in progress: there are still more functions to be implemented and the functionality of existing functions may change.

Syntax

Like other LISP languages, JL uses s-expressions. For example:

(list 1 2 3)

calls the "list" function, passing 1, 2, and 3 as arguments.

Data Types

There are 6 data types:

1. Numbers (floating point numbers)
2. Strings
3. Variables
4. Lambdas (functions defined within the language)
5. Lists
6. Special functions

For comparisons, 0 and nil (the empty list) are considered false and all other values are considered true.

Functions

The following built-in functions are available:

• < Test if less than

•    Test if greater than
  

• <= Test if less than or equal to

• = Test if greater than or equal to

• = Test if equal
• != Test if not equal

• •    Return the sum of a list
    

• •    Subtract
    

• •    Return the produce of a list
    

• / Divide
• % Modulus
• and Logical AND.
• concat Concatenate strings.
• cons Prepend an item to a list.
• begin Execute a sequence of functions, return the value of the last.
• define Insert a binding into the current namespace.
• head Return the first element of a list
• if Test a condition and evaluate and return the second argument if true, otherwise evaluate and return the third argument.
• lambda Declare a function.
• list Create a list
• list? Determine if a value is a list.
• not Logical NOT.
• null? Determine if a value is nil.
• number? Determine if a value is a number.
• or Logical OR.
• rest Return all but the first element of a list
• string? Determine if a value is a string.
• substr Return a substring of a string.

Examples

Here are some example programs. See the "examples" directory for more.

Return the factorial of a number: <code><pre> (define fact (lambda (n) (if n (* (fact (- n 1)) n) 1))) (fact 5) </pre></code>

Find the nth item of a list: <code><pre> (define nth (lambda (n lst) (if (<= n 1) (head lst) (nth (- n 1) (rest lst))))) (nth 2 (list 1 2 3)) </pre></code>

Find nth Fibonacci number: <code><pre> (define fib (lambda (n) (if (> n 1) (+ (fib (- n 1)) (fib (- n 2))) 1))) (fib 10) </pre></code>

The map function: <code><pre> (define map (lambda (f lst) (if lst (cons (f (head lst)) (map f (rest lst))) (list)))) (map (lambda (x) (+ x 1)) (list 1 2 3 4)) </pre></code>

The foldl function: <code><pre> (define foldl (lambda (f i lst) (if lst (foldl f (f i (head lst)) (rest lst)) i))) (foldl (lambda (a b) (+ a b)) 0 (list 1 2 3 4)) </pre></code>

The reverse function implemented in terms of foldl: <code><pre> (define reverse (lambda (lst) (foldl (lambda (a b) (cons b a)) (list) lst))) (reverse (list 1 2 3 4)) </pre></code>

License

JL uses the BSD 2-clause license. See LICENSE for more information.