[Haskell-cafe] Parsing, infixes and on-the-fly precedence

I imagine a parser that operates on (String,[String]) pairs, for which the second element allows the user to define precedence on the fly. For instance, it would read the pair (x,y) = ("a , b : c", [":" , ","]) as "(a , (b : c))" because y informs the parser that in x the colon binds first, then the comma. I know it is possible, because Haskell does it already! In Haskell we can define novel infix operators on the fly, including their precedence relative to each other. I don't know how, though, so that's my question. -- Jeffrey Benjamin Brown