If don't have to use Parsec, you can use a parser library like ReadP / ReadS.

For example:

import Text.ParserCombinators.ReadP

abc = (choice [ string "a", string "ab" ] ) >> char 'c' >> eof

run p s = case (readP_to_S p) s of

[] -> Left "no parse"

((a,_):_) -> Right a

test1 = run abc "ac"

test2 = run abc "abc"

test3 = run abc "ab" -- should fail

On Monday, May 30, 2016 at 1:15:25 PM UTC-5, Petr Sokolov wrote:

For example this parser doesn't parse "abc"

test :: Parser String
test = ((try $ string "a") <|> (string "ab")) *> (string "c")

I can rewrite it so it would parse "abc", but is there any general approach to force parser to return and try other branches?

(try a <|> b) *> c

Something like

(tryOtherBranchesIfFail (try a <|> b)) *> c

So if it cannot parse "abc" with (try a *> c) it could return and try (b *> c)
Or it isn't possible?