Lets say i have
data A = B Char Integer
and I have a variable called var in type A.
How can I access the integer value of var variable and use it?
Is there any operator to get it? I don't know, something like var->int would give me it?
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2 Answers
You can define a function for this using pattern matching:
getIntegerFromA :: A -> Integer
getIntegerFromA (B _ int) = int
Though depending on where you want to use it, you can probably get the value using pattern matching right there instead of defining a separate function.
6 Comments
geekosaur
You can also have Haskell define what are referred to (somewhat confusingly for people coming from OO languages) as "destructors" for you: change the definition to
data A = B {charval :: Char, intval :: Integer}. Now you can use intval var to get at it.
thetux4
I think using pattern matching somehow makes more sense to me, but thanks for the answers.
geekosaur
@sepp2k: Untrue,
B 'c' 5 still works, as does pattern matching against it. See the heading "Labelled Fields" in the Online Report.
John L
@geekosaur: I think this is more commonly referred to as "record syntax".
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The other way is to use "record syntax", which generates the accessor functions automatically, but many people consider ugly and un-Haskell like.
