debug

A lang-extension for debugging, based on sugar/debug from mbutterick/sugar

documentation: http://pkg-build.racket-lang.org/doc/debug/index.html

#lang debug

To debug the value of an expression, simply put debug in front of the language at the top of the file (for instance #lang debug racket), and put #R, #RR or #RRR in front of the expression.

• #R reports the value and returns it
• #RR reports the value with a line number and returns it
• #RRR reports the value with the file and line number, and returns it

#lang debug racket
#R(+ 1 2)

Shows the output:

(+ 1 2) = 3
3

#lang debug racket
(+ 1 2 #R(* 3 4))

Shows the output:

(* 3 4) = 12
15

#lang debug/no-output

Allows #R, #RR and #RRR like #lang debug, but they don't add any debug output, they just return the expression inside.

debug-repl

> (require debug/repl)
> (define (f x y)
    (debug-repl))
> (f 1 2)
-> ; in the debug-repl now
   x
1
-> y
2
-> (+ x y)
3
-> ; exit the debug-repl by pressing ctrl-D
> ; back in the normal repl
  (f (λ (g a) (g a)) (list add1 4))
-> ; a new debug-repl
   x
#<procedure>
-> y
(list #<procedure:add1> 4)
-> (x string->number "3")
3
-> (x (first y) (second y))
5
-> ; exit this debug-repl by pressing ctrl-D