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52 lines
1.6 KiB
Racket
52 lines
1.6 KiB
Racket
#lang scribble/manual
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@(require scribble/eval (for-label racket sugar))
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@(define my-eval (make-base-eval))
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@(my-eval `(require sugar))
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@title{Debug}
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@defmodule[sugar/debug]
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Debugging utilities.
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@defform[(report expr)]
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Print the name and value of @racket[_expr] to @racket[current-error-port], but also return the evaluated result of @racket[_expr] as usual. This lets you see the value of an expression or variable at runtime without disrupting any of the surrounding code.
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For instance, suppose you wanted to see how @racket[first-condition?] was being evaluted in this expression:
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@racketblock[
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(if (and (first-condition? x) (second-condition? x))
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(one-thing)
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(other-thing))]
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You can wrap it in @racket[report] and find out:
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@racketblock[
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(if (and (report (first-condition? x)) (second-condition? x))
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(one-thing)
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(other-thing))]
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This code will run the same way as before. But when it reaches @racket[first-condition?], you willl see in @racket[current-error-port]:
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@racketerror{(first-condition? x) = #t}
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You can also add standalone calls to @racket[report] as a debugging aid at points where the return value will be irrelevant, for instance:
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@racketblock[
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(report x)
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(if (and (report (first-condition? x)) (second-condition? x))
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(one-thing)
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(other-thing))]
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@racketerror{x = 42
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@(linebreak)(first-condition? x) = #t}
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But don't do this, because the result of the @racket[if] expression will be skipped in favor of the last expression, which will be the value of @racket[_x]:
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@racketblock[
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(if (and (report (first-condition? x)) (second-condition? x))
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(one-thing)
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(other-thing))
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(report x)]
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