I've written a Marpa-powered utility that reports mismatched brackets
<https://gist.github.com/jeffreykegler/b6bfeeadfcedeade6519> in the set
() {} []. It was written as a demo, but is quite useable as it is --
you may find it more accurate than the native compiler/interpreter for
your language.
It works using the Ruby Slippers. It uses the new rejection events to
stop parsing whenever the parser rejects all lexemes, so that the
application can dummy up a new "Ruby Slippers" token. It makes its best
guess as to how to correct the problem and proceeds. This makes the
parse "self-correcting", allowing the utility to accurately diagnose a
series of mismatched parentheses. Traditional parsers are usually
hopeless after the first mismatch, and not any too clever about the
first one.
To be sure, ultimately it comes down to the programmer's intent, but I
think you'll find this utility is highly accurate in most practical
situations. The formatting of the reports is (I hope) helpful. For the
string '((([))', the diagnostics are:
* Line 1, column 1: Opening '(' never closed, problem detected at end
of string
((([))
^
====================
* Line 1, column 4: Missing close ], problem detected at line 1, column 5
((([))
^^
Marpa is left-eidetic -- it knows everything about the parse to the left
of the current position, and the utility exploits this. For the string
'[({({x[]x{}x()x)})]', it spots the extra closing ')' at column 16, but
it's also able to tell *why* it's wrong. It cannot accept the ')' at
column 16, without first closing the set of curly braces started at
column 5. Maybe your compiler is giving you this sort of feedback, but
I doubt it.
* Line 1, column 5: Missing close }, problem detected at line 1, column 16
[({({x[]x{}x()x)})]
^ ^
While this utility is already useful, I think of it as a prototype for
what could be done. This problem -- matching delimiters -- is in fact
very general, and I believe these techniques have very wide application.
-- jeffrey
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