I don't have experience solving this problem, but I've read a few
horror stories from people who had state affect the results of parsing
in Parsec.
Haskell's layout rules replace indentation levels with braces and
semicolons; you could run an initial "tokenizing" parser that builds
tokens including the indentation level of each line, then convert
those tokens into the appropriate braces and semicolons (via a pure
function) before feeding the results into the "real" Haskell parser.
-- ryan
On Mon, Apr 27, 2009 at 2:41 PM, Bas van Gijzel
Hello everyone,
I'm doing a bachelor project focused on comparing parsers. One of the parser libraries I'm using is Parsec (2) and I'm going to implement a very small subset of haskell with it, with as most important feature the off-side rule (indentation based parsing) used in function definitions and possibly in where clauses.
But I'm still a bit stuck on how to implement this cleanly. I tried to search for some examples on blogs but I haven't found anything yet. As far as I can see the way to go would be using getState and updateState methods defined in Parsec.Prim and to use the methods in Parsec.Pos to compare the difference in indendation for tokens.
But I haven't completely wrapped my head around any state monad yet and I don't understand Parsec enough yet to see how to use the methods Parsec.Pos and state easily. Some examples or pointers to something to read would really be helpful.
Thanks in advance,
Bas van Gijzel
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