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#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) (report expr maybe-name))]
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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. Optionally, you can use @racket[_maybe-name] to change the name shown in @racket[current-error-port].
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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 x-before-function)
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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-before-function = 42
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@(linebreak)(first-condition? x) = #t}
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But be careful — in the example below, 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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@defform[(report* expr ...)]
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Apply @racket[report] separately to each @racket[_expr] in the list.
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@defform[(repeat num expr ...)]
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Evaluate @racket[_expr] repeatedly — @racket[_num] times, in fact — and return the last value.
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@examples[#:eval my-eval
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(repeat 1000
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(for/sum ([i (in-range 1000)]) i))
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]
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@defform[(time-repeat num expr ...)]
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Shorthand for using @racket[time] with @racket[repeat]. Repeat the whole list of expressions, print the total time, and return the last value.
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@examples[#:eval my-eval
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(time-repeat 1000
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(for/product ([i (in-range 1000)]) i)
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(for/sum ([i (in-range 1000)]) i))
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]
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@defform[(time-repeat* num expr ...)]
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Apply @racket[time-repeat] to each @racket[_expr] individually.
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@examples[#:eval my-eval
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(time-repeat* 1000
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(for/product ([i (in-range 1000)]) i)
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(for/sum ([i (in-range 1000)]) i))
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]
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@defform[(compare expr id id-alt ...)]
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Evaluate @racket[_expr] first using @racket[_id], and then again substituting @racket[_id-alt] in place of @racket[_id], and then again for every other @racket[_id-alt] in the list. This is useful for comparing the performance of multiple versions of a function.
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@examples[#:eval my-eval
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(define (fib x)
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(if (< x 2) 1 (+ (fib (- x 1)) (fib (- x 2)))))
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(define/caching (fib-fast x)
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(if (< x 2) 1 (+ (fib-fast (- x 1)) (fib-fast (- x 2)))))
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(compare (time (fib 34)) fib fib-fast)
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]
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