If I understand you correctly, what you want is very similar to catMaybes
isSuccess' (Success a) = Just a
isSuccess' _ = Nothing
result = catMaybes $ map isSuccess ps
This should do the trick.
2010/1/7 rodrigo.bonifacio
Hi all,
I have a family of parsers that return either (Success t) or (Fail), using the following data type:
data ParserResult a = Success a | Fail String deriving (Read, Show, Eq, Ord)
isSuccess (Success _) = True isSuccess (Fail _) = False ...
I want to add the results of different parsers to a list. Such as:
m1 = parseFirstModel file1 -- it returns a ParserResult of t1 m2 = parseSecondModel file2 -- it returns a ParserResult of t2
ps = [m1, m2]
In such a way that I could write something like:
if and (map isSuccess ps) then process m1 m2 else ...
Actually, in the real program I have to check more than two input models. However, since Lists do only hold elements of a same type, I couldn't proceed in this way. Which improvements to the ParserResult data type should I wrote in order to proceed as I want to.
Best regards,
Rodrigo.
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