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Cleans up the debugging advice section

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Casey Klein 2010-07-27 15:42:38 -05:00
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1 changed files with 23 additions and 17 deletions
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@ -1395,27 +1395,33 @@ produces and consumes argument lists.}
@deftech{Debugging PLT Redex Programs}
It is easy to write grammars and reduction rules that are
subtly wrong and typically such mistakes result in examples
that just get stuck when viewed in a @racket[traces] window.
subtly wrong. Typically such mistakes result in examples
that get stuck when viewed in a @racket[traces] window.
The best way to debug such programs is to find an expression
that looks like it should reduce but doesn't and try to find
out what pattern is failing to match. To do so, use the
@racket[redex-match] special form, described above.
that looks like it should reduce, but doesn't, then try to find
out which pattern is failing to match. To do so, use the
@racket[redex-match] form.
In particular, first ceck to see if the term matches the
main non-terminal for your system (typically the expression
or program nonterminal). If it does not, try to narrow down
the expression to find which part of the term is failing to
match and this will hopefully help you find the problem. If
it does match, figure out which reduction rule should have
matched, presumably by inspecting the term. Once you have
that, extract a pattern from the left-hand side of the
reduction rule and do the same procedure until you find a
small example that shoudl work but doesn't (but this time
you might also try simplifying the pattern as well as
simplifying the expression).
In particular, first check if the term in question matches the
your system's main non-terminal (typically the expression
or program non-terminal). If it does not match, simplify the term
piece by piece to determine whether the problem is in the
term or the grammar.
If the term does match your system's main
non-terminal, determine by inspection which reduction rules
should apply. For each such rule, repeat the above term-pattern
debugging procedure, this time using the rule's left-hand side
pattern instead of the system's main non-terminal. In addition
to simplifying the term, also consider simplifying the pattern.
If the term matches the left-hand side, but the rule does not
apply, then one of the rule's @racket[side-condition] or
@racket[where] clauses is not satisfied. Using the bindings
reported by @racket[redex-match], check each @racket[side-condition]
expression and each @racket[where] pattern-match to discover which
clause is preventing the rule's application.
@section{GUI}
@defmodule[redex/gui]