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:

(define fact (lambda (n)
(if n
(* (fact (- n 1)) n)
1)))
(fact 5)

Find the nth item of a list:

(define nth (lambda (n lst)
(if (<= n 1)
(head lst)
(nth (- n 1) (rest lst)))))
(nth 2 (list 1 2 3))

Find nth Fibonacci number:

(define fib (lambda (n)
(if (> n 1)
(+ (fib (- n 1)) (fib (- n 2)))
1)))
(fib 10)

The map function:

(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))

The foldl function:

(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))

The reverse function implemented in terms of foldl:

(define reverse (lambda (lst) (foldl (lambda (a b) (cons b a)) (list) lst)))
(reverse (list 1 2 3 4))

License

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