[Haskell-cafe] simple parsing

[Thomas Danecker]

Your pattern in the head of the function "chromoResult (a:b:c:xs)"
requires the list to have at least three elements in it. I doubt that
all the recursive calls take this into consideration...

2009/10/27 satorisanitarium <satorisanitarium at gmail.com>:
> I'm trying to parse a list of numbers plus four diferent signs (+-*/)
> in this way:
>
> Lets say the list is "32+5/46" result would be "2+5/4"
> I get:
>
> "2+5/4*** Exception: geneticSimple.hs:(55,0)-(65,35): Non-exhaustive
> patterns in function chromoResult
>
> If the list is "32+5**6" result would be "2+5*6"
> I get:
> "2+5/*** Exception: geneticSimple.hs:(55,0)-(65,35): Non-exhaustive
> patterns in function chromoResult
>
> If the list is "32+-72" resoult would be "2+7"
> I get:
> "2+*** Exception: geneticSimple.hs:(55,0)-(65,35): Non-exhaustive
> patterns in function chromoResult
>
> code:
>
> chromoResult [] = []
> chromoResult (a:b:c:xs)
>        | elem a "0123456789" && elem b "0123456789" && elem c "0123456789" =
> chromoResult (c:xs)
>        | elem a "0123456789" && elem b "0123456789" && elem c "+-*/" = b:c:
> chromoResult xs
>        | elem a "0123456789" && elem b "+-*/" && elem c "0123456789" =
> a:b:c : chromoResult xs
>        | elem a "0123456789" && elem b "+-*/" && elem c "+-*/" = a:b :
> chromoResult (c:xs)
>        | elem a "+-*/" && elem b "0123456789" && elem c "0123456789" =
> chromoResult (b:c:xs)
>        | elem a "+-*/" && elem b "0123456789" && elem c "+-*/" = b:c :
> chromoResult xs
>        | elem a "+-*/" && elem b "+-*/" && elem c "0123456789" =
> chromoResult (c:xs)
>        | elem a "+-*/" && elem b "+-*/" && elem c "+-*/" = chromoResult xs
>        | otherwise = chromoResult (b:c:xs)
>
> I suspect my approach is flawed but i have exausted my ideas.
> I need  a fresh approach so if anybody would be kind enough and just
> give me a hint how to approach the problem.
> Thx in advance.
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