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.
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