I used to debug parsing process for VHDL grammar (which is ambiguous on lexem level) with parsing combinators and Haskell REPL.
Whenever my "compiler" found a syntax error in test suite, I was able to load part of source around error and investigate where my parser's error or omission is by running parser of smaller and smaller part of grammar on smaller and smaller parts of input.
Whenever my "compiler" found a syntax error in test suite, I was able to load part of source around error and investigate where my parser's error or omission is by running parser of smaller and smaller part of grammar on smaller and smaller parts of input.
It was 12 years ago.
And yes, it is fun. ;)