02_lisp

go-lisp.go

A simple Lisp interpreter developed in Go.

Go is a perfect fit for building a Lisp interpreter, since it's portable, garbage collected and fast. The result is a one file distribution, which makes it easy to deploy. The garbage collection unloads that work from the interpreter, using the Go already tuned GC.

Inspired by: [http://norvig.com/lispy.html]

Setup

Install Go

http://golang.org/doc/install

Make sure your GOPATH is setup correctly, something like

$ export GOPATH=$HOME/go
$ mkdir -p $GOPATH

Clone the repo

$ go get github.com/janne/go-lisp

Run the tests

$ go test github.com/janne/go-lisp/lisp

Run the example

$ go-lisp -file $HOME/go/src/github.com/janne/go-lisp/example.lsp

Run it interactively

$ go-lisp -i

Syntax

(quote exp)

Return the exp literally; do not evaluate it.

(quote (a b c))

Returns:

(a b c)

(if test conseq alt)

Evaluate test; if true, evaluate and return conseq; otherwise evaluate and return alt.

(if (< 10 20) (+ 1 1) (+ 3 3))

Returns:

2

(set! var exp)

Evaluate exp and assign that value to var, which must have been previously defined (with a define or as a parameter to an enclosing procedure).

(set! x2 (* x x))

(define var exp)

Define a new variable and give it the value of evaluating the expression exp.

(define r 3)
(define square (lambda (x) (* x x)))

(lambda (var...) exp)

Create a procedure with parameter(s) named var... and the expression as the body.

(lambda (r) (* 3.141592653 (* r r)))

(begin exp...)

Evaluate each of the expressions in left-to-right order, and return the final value.

(begin (define x 1) (set! x (+ x 1)) (* x 2))

Returns:

4

(proc exp...)

If proc is anything other than one of the symbols if, set!, define, lambda, begin, or quote then it is treated as a procedure. It is evaluated using the same rules defined here. All the expressions are evaluated as well, and then the procedure is called with the list of expressions as arguments.

(square 12)

Returns:

144

License

Licensed under MIT license.