danlisp

README

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Running

To get a basic REPL

go run cmd/danlisp/danlisp.go

To run a file

go run cmd/danlisp/danlisp.go <filename>

Examples

There are example programs here

Syntax

DanLisp uses paranthesized prefix notation, which will be familiar to anyone who has seen any other Lisp-like language.

Literals

There are three types of literal so far; strings, numbers and nil.

eg

3
3.0
3.35
"foo"
"bar"
nil

Operators

All the basic mathematical operators are present

(+ 2 2)
(- 12 7)
(* 5 2)
(/ 100 5)

Equality is a single =

(= 2 2)

Operators can be nested unambiguously

(+ 2 (- 10 5))
(+ (- 2 10) 5)

There are also logical operators for comparison, lt and gt for less than and greater than.

(lt 2 10)
(gt 1000 10)

There are boolean operators for combining conditions

(and (= 2 2) (= 4 (+ 2 2)))
(or (= 2 2) (= 5 (+ 2 2)))

Built-ins

Printing to stdout is done with prn

(prn "Hello world")
(set name "Dan")
(prn "Hello" name)

If prn is given more than one argument it will print them all with a seperating space.

Variables

Variables can be declared using set

(set i 10)
(set name "Dan")

Variables are fully mutable. Example of incrememnting a variable.

(set count 1)
(set count (+ count 1))

It is possible to overwrite any builtin functions and keywords with user defined variables but don't do this.

If

The if function will execute the first branch if the condition is true, and the second if it is false. It has the form

(if cond
    true-branch
    false-branch)

For example

(if (gt 99999 n)
    (prn n "is a really big number")
    (prn n "is not that big"))

Conditionals

Any value that is not nil will evaluate to true. For conveniance the symbol t is provided and is set to true.

Loops

There is one type of loop in DanLisp currently, the while loop of the form.

(while cond
    body)

For example to print "hello world" forever,

(while t
    (prn "hello world"))

You can simulate a for loop with a more verbose while,

(set i 1)
(while (lt i 10)
    (prn "Square of" i "is" (* i i))
    (set i (+ i 1)))

Functions

Functions can be defined using defn in the form of

(defn function-name (arglist)
    body)

For example a function that says hello

(defn say-hello (name)
    (prn "Hello" name))

or a function to add two numbers

(defn adder (a b)
    (+ a b))

The last expression in the function will implicitly be the return value. There is no way to return early.