Convert a Racket string to a Racket procedure/function

str2proc.rkt

#lang racket/base

#|
String -> Procedure

A way to convert a Racket string into a procedure object.

This is done by hot-code evaluation. Since there's no built-in
method to convert anything to a procedure other than defining
the procedure itself, this lets us check if a string is indeed
a procedure in the current runtime namespace.

This can be used in syntax highlighting beyond the normal
pre-defined keyword/method lists way of highlighting code.
You can check if functions are actually defined in the 
Racket namespace and highlight that way.

|#

;; Define a namespace anchor, or really just a reference
;; to the current Racket namespace
(define-namespace-anchor a)

;; Convert a string to a procedure
;; Note: no contracts/type checking provided (very lazy)
;; Returns #f if no procedure can be found/evaluated
(define (string->procedure procstr)
  (define cn (namespace-anchor->namespace a))
  (define procsym (string->symbol procstr))
  (parameterize ([current-namespace cn])
    (eval `(cond [procedure? ,procsym]
                 [else #f]))))

;; Define the id function :: a -> a
(define (id x) x)

;; Test the function/playground
(module+ main
  (displayln "Testing string->procedure")
  (displayln (format "Should give #<procedure:+> => ~a" (string->procedure "+")))
  (define plus (string->procedure "+"))
  (displayln (format "Doing addition with it (+ 2 2) => ~a" (plus 2 2)))
  (define sid (string->procedure "id"))
  (displayln "Testing string->procedure on defined id func")
  (displayln (format "Should give #<procedure:id> => ~a" sid))
  (displayln (format "Testing (sid 3) = 3 => ~a" (sid 3)))
  )

; end