markcol/goscheme

goscheme

A R5RS-compliant Scheme interpreter in Go.

Go is a great language for or building a Scheme 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 Go's GC.

Setup

Run the example

$ goscheme -file $GOPATH/src/github.com/markcol/goscheme/example.scm

Run it interactively

$ goscheme -i

Syntax

---

(quote exp)

Return exp literally; do not evaluate it.

(quote (a b c))

or

'(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 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...) body)

Create a procedure with parameter(s) named var and the expression body 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, and then the procedure is called with the list of expressions as arguments.

(square 12)

Returns:

144