== debug

Some trivial debugging macros
[[toc:]]
=== Abstract
According to [[http://books.google.com/books?id=nneBa6-mWfgC&lpg=PA227&ots=gEvyGdNW3u&dq=%22thou%20shalt%20put%20printf%22&pg=PA227#v=onepage&q=%22thou%20shalt%20put%20printf%22&f=false|Joe Armstrong]], "The great gods of programming said, 'Thou shalt put {{printf}}
statements in your program at the point where you think it’s gone
wrong, recompile, and run it.'"


=== Documentation
==== {{debug?}}
<parameter>debug? → #t</parameter>
`debug?' turns on or off debugging output, depending on whether
it is set to #t or #f; respectively.
<enscript highlight="scheme">(define debug? (make-parameter #t))
</enscript>
==== {{trace}}
<syntax>(trace f) → unspecified</syntax>
Trace the input to and output from a function.
; f : The function to be traced
<enscript highlight="scheme">(define-syntax
  trace
  (er-macro-transformer
    (lambda (expression rename compare)
      (match-let
        (((_ f) expression))
        (let ((%set! (rename 'set!))
              (%lambda (rename 'lambda))
              (%call-with-values (rename 'call-with-values))
              (%apply (rename 'apply))
              (%format (rename 'format))
              (%values (rename 'values))
              (%let (rename 'let))
              (%f (rename 'f))
              (%when (rename 'when))
              (%debug? (rename 'debug?)))
          `(,%when
            (,%debug?)
            (,%let
             ((,%f ,f))
             (,%set!
              ,f
              (,%lambda
               x
               (,%format (current-error-port) ";; Arguments to ~a: ~a~%" ',f x)
               (,%let
                ((return-values
                   (,%call-with-values
                    (,%lambda () (,%apply ,%f x))
                    (,%lambda x x))))
                (,%format
                 (current-error-port)
                 ";; Values from ~a: ~a~%"
                 ',f
                 return-values)
                (,%apply ,%values return-values)))))))))))
</enscript>
==== {{debug}}
<syntax>(debug expressions) → unspecified</syntax>
Debug the expressions to stderr by pretty-printing each
expression and their evaluations.
; expressions : The expressions to be debugged
<enscript highlight="scheme">(define-syntax
  debug
  (syntax-rules
    ()
    ((_ x ...)
     (with-output-to-port
       (current-error-port)
       (lambda ()
         (when (debug?)
               (pp `(,(if (or (boolean? 'x)
                              (char? 'x)
                              (number? 'x)
                              (string? 'x)
                              (vector? 'x))
                        x
                        `(x =>
                            ,(handle-exceptions
                               exn
                               (let ((message
                                       ((condition-property-accessor 'exn 'message) exn))
                                     (arguments
                                       ((condition-property-accessor 'exn 'arguments)
                                        exn)))
                                 (format
                                   "Error: ~a~a"
                                   message
                                   (if (null? arguments)
                                     ""
                                     (format
                                       ": ~a"
                                       (string-join (map ->string arguments) ", ")))))
                               x)))
                     ...))))))))
</enscript>
==== {{debug-priority}}
<parameter>debug-priority → prio/debug</parameter>
The priority associated with {{debug/syslog}}
<enscript highlight="scheme">(define debug-priority (make-parameter prio/debug))
</enscript>
==== {{debug/syslog}}
<syntax>(debug/syslog expressions) → unspecified</syntax>
Debug to syslog.
; expressions : The expressions to debug (cf. `debug' supra)
<enscript highlight="scheme">(define-syntax
  debug/syslog
  (ir-macro-transformer
    (lambda (expression rename inject)
      `(let ((port (make-syslog-port)))
         (with-error-output-to-port
           port
           (lambda ()
             (when (debug?)
                   (debug ,@(cdr expression))
                   (flush-output port))))))))
</enscript>
=== About this egg

==== Author

[[/users/klutometis|Peter Danenberg]]
==== Repository
[[https://github.com/klutometis/debug]]
==== License
BSD
==== Dependencies
* [[cock]]
* [[matchable]]
* [[setup-helper]]
* [[setup-helper-cock]]
* [[syslog]]

==== Versions
; 0.1 : Version 0.1
; 0.1.1 : Version 0.1.1
; 0.1.2 : BSD
; 0.2 : Add a `debug?'-parameter.
; 0.3 : Add exception-guard; document.
; 0.3.1 : Add "Error: ..."
; 0.3.2 : Add arguments in errors.
; 0.3.3 : Don't do arguments if we don't have to.
; 0.3.4 : With a note about cock-utils
; 0.3.5 : Add test-exit.
; 0.3.6 : Disable an offending test.
; 0.3.7 : Self-evaluating scalars
; 0.3.8 : Fix tests
; 0.3.9 : Fix debug/syslog.
; 0.3.10 : Default-priority -> debug-priority
==== Colophon

Documented by [[/egg/cock|cock]].