On Tue, Oct 27, 2009 at 11:38 PM, satorisanitarium wrote:

I'm trying to parse a list of numbers plus four diferent signs (+-*/) in this way:

*snip*

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.

To begin with, try using the Parsec parser-combinator library instead of writing your own from scratch? -- Svein Ove Aas

Ok, I think this is a weird problem, but let us start. You want to parse a sequence of operands separated by an operator (we assume the ops are left associative): import Text.ParserCombinators.UU.Parsing pWeird = pChainl pOperator pOperand An operand is apparently a non-empty list of digits, and the result should be the last of these digits: pOperand = toList.last <$> pList1 (pSym ('0', '9')) toList x = [x] An operator is a sequence of "+-/*" symbols, and it is the first element in which you are interested: pOperator = intoOp.head <$> pList1 (pSym '+' <|> pSym '-' ...) The function intoOp now builds the function which constructs the final list given the operator and the left and right operands: intoOp op = \leftop rightop -> leftop ++ [op] ++ rightop Doaitse On 27 okt 2009, at 23:38, satorisanitarium wrote:

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. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe