2010/1/12 Günther Schmidt
[Snip...] I need to write my own parsec-token-parsers to parse this token stream in a context-sensitive way.
Uhm, how do I that then?
Hi Günther Get the Parsec manual from Daan Leijen's home page then see the section '2.11 Advanced: Seperate scanners'. Though mentioned rarely, Parsec in its regular mode is a scannerless parser. Unless you have complex formatting problems (e.g. indentation sensitivity, vis Python or Haskell's syntax) scannerless parsers are often much more convenient than parsers+lexers (see the grammar formalism SDF for many examples). For Parsec, if you want a separate scanner there's quite a lot of boilerplate you need to manufacture if you want to use the technique in section 2.11. Usually I can get by with the Token and Language modules or do a few tricks with the 'symbol' parser instead. Parsec is monadic so (>>=) allows you to write context-sensitive parsers, see section '3.1. Parsec Prim' for a discussion and example. Again, writing a context-sensitive parser can often be more trouble than studying the format of the input and working out a context-free grammar (if there is one). Best wishes Stephen