Print debugging statement: Difference between revisions
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Show the print debugging statements in the language. If possible, demonstrate their ability to display information about source code (e.g., code fragment, line number). |
Show the print debugging statements in the language. If possible, demonstrate their ability to display information about source code (e.g., code fragment, line and column number). |
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=={{header|Pyret}}== |
=={{header|Pyret}}== |
Revision as of 13:53, 27 August 2019
From Wikipedia:
Print debugging (or tracing) is the act of watching (live or recorded) trace statements, or print statements, that indicate the flow of execution of a process. This is sometimes called printf debugging, due to the use of the printf function in C.
- Task
Show the print debugging statements in the language. If possible, demonstrate their ability to display information about source code (e.g., code fragment, line and column number).
Pyret
Pyret has the spy
expression. The expression can print the value of an identifier, using the identifier itself as a label if it's not already given. It could also print the value of an arbitrary expression, but it needs an explicit label in this case.
<lang pyret>fun add(x, y):
result = x + y spy "in add": x, y, result, result-plus-one: result + 1 end result
end
add(2, 7)</lang>
- Output:
Spying "in add" (at file:///spies.arr:3:2-8:5) x: 2 y: 7 result: 9 result-plus-one: 10 9
Racket
Racket doesn't have a built-in print debugging statement. However, it can be defined by users as a macro.
<lang racket>#lang racket
(require syntax/parse/define)
(define (debug:core line col code val #:label [label #f])
;; if label exists, use it instead of the code fragment (printf "~a at line ~a column ~a\n" (or label code) line col) (printf "result: ~a\n\n" val) ;; return the value itself, so that we can wrap macro around an expression ;; without restructuring any code val)
(define-simple-macro (debug <x> option ...)
#:with line (datum->syntax this-syntax (syntax-line #'<x>)) #:with col (datum->syntax this-syntax (syntax-column #'<x>)) (debug:core line col (quote <x>) <x> option ...))
(define (add x y)
(define result (+ x y)) (debug x) (debug y) (debug (if #t (+ x y) (error 'impossible))) (debug (add1 result) #:label "result plus one") (debug result))
(add 2 7)</lang>
- Output:
x at line 20 column 9 result: 2 y at line 21 column 9 result: 7 (if #t (+ x y) (error 'impossible)) at line 22 column 9 result: 9 result plus one at line 23 column 9 result: 10 result at line 24 column 9 result: 9 9