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\begin{code}
{-# LANGUAGE NoImplicitPrelude #-}
module Text.RE.ZeInternals.Tools.Lex
( alex
, alex'
) where
import Prelude.Compat
import Text.RE.Replace
import Text.RE.ZeInternals.Types.IsRegex
\end{code}
\begin{code}
-- | a simple regex-based scanner interpretter for prototyping
-- scanners
alex :: IsRegex re s => [(re,Match s->Maybe t)] -> t -> s -> [t]
alex = alex' matchOnce
-- | a higher order version of 'alex' parameterised over the @matchOnce@
-- function
alex' :: Replace s
=> (re->s->Match s)
-> [(re,Match s->Maybe t)]
-> t
-> s
-> [t]
alex' mo al t_err = loop
where
loop s = case lengthR s == 0 of
True -> []
False -> choose al s
choose [] _ = [t_err]
choose ((re,f):al') s = case mb_p of
Just (s',t) -> t : loop s'
_ -> choose al' s
where
mb_p = do
cap <- matchCapture mtch
case captureOffset cap == 0 of
True -> (,) (captureSuffix cap) <$> f mtch
False -> Nothing
mtch = mo re s
\end{code}