[clean-list] Parser, why three type variables

[Carlos Aya]

Hello,

In the parsers library one finds...

:: Parser s r t

and 

parse :: !(Parser s r r) [s] String String -> Result r

Still not clear for me, from a software design point of view, why three type variables in 'Parse' if 'parse' use only 2 in the type? Why we want the type engine to have that free 't' around? I saw the combinators and none of them touch it... hope I didn't overlooked something... any help appreciated.

regards
Carlos



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