# [racket] How to create 'Internal Definitions' in a scheme interpreter.

Hi,
I am writing my first interpreter, but I am struggling with the
definitions of 'define', 'let' and 'letrec'.
Here is the source code intrepreter (> 100 loc) . http://gist.github.com/487501
The problem is that 'define' requires access to the enviroment. I as
understand define is equivalent to these expansions.
==== Top level.
(define (foo)
(... (bar) ...))
=> Will be
(define foo
(lambda ()
(... (bar) ...)))
==== In a lambda environment.
(define (my-proc)
(define (local-proc-1)
...)
(define (local-proc-2)
...)
(local-proc-1)
(local-proc-1))
=> Will be
(define my-proc
(lambda ()
(letrec ((local-proc-1 (lambda () ...))
(local-proc-2 (lambda () ...)))
(local-proc-1)
(local-proc-2)))
Can anyone point me how to implement this features. I am trying to
implement them out of the evaluator function, but I guess that if they
need access to the environment, maybe they should be inside of the
evaluator method. Maybe something like this?
[`(letrec ,binds ,eb)
(eval-letrec binds eb env)]
[`(let ,binds ,eb)
(eval-let binds eb env)]
; eval for letrec:
(define (eval-letrec bindings body env)
(let* ((vars (map car bindings))
(exps (map cadr bindings))
(fs (map (lambda _ #f) bindings))
(env* (extended-env* env vars fs))
(vals (map (evlis env*) exps)))
(env-set!* env* vars vals)
(eval body env*)))
; eval for let:
(define (eval-let bindings body env)
(let* ((vars (map car bindings))
(exps (map cadr bindings))
(vals (map (evlis env) exps))
(env* (extended-env* env vars vals)))
(eval body env*)))
(define ? )
I am new in this list, so let me know if this question is "off-topic".
Thx.
--
-------------------------------------
Pedro Del Gallego
Email : pedro.delgallego at gmail.com