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Packrat Parsing
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data Result v = Parsed v Derivs | |
| NoParse | |
data Derivs = Derivs { | |
dvAdditive :: Result Int, | |
dvMultitive :: Result Int, | |
dvPrimary :: Result Int, | |
dvDecimal :: Result Int, | |
dvChar :: Result Char} | |
parse :: String -> Derivs | |
parse s = d where | |
d = Derivs add mult prim dec chr | |
add = pAdditive d | |
mult = pMultitive d | |
prim = pPrimary d | |
dec = pDecimal d | |
chr = case s of | |
(c:s') -> Parsed c (parse s') | |
[] -> NoParse | |
pAdditive :: Derivs -> Result Int | |
pAdditive d = alt1 where | |
alt1 = case dvMultitive d of | |
Parsed vleft d' -> | |
case dvChar d' of | |
Parsed '+' d'' -> | |
case dvAdditive d'' of | |
Parsed vright d''' -> | |
Parsed (vleft + vright) d''' | |
_ -> alt2 | |
_ -> alt2 | |
_ -> alt2 | |
alt2 = dvMultitive d | |
pMultitive :: Derivs -> Result Int | |
pPrimary :: Derivs -> Result Int | |
pDecimal :: Derivs -> Result Int |
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