combine pattern matching against named fields and tuples
I'm trying to do something like this: data Thing = Thing { field1, field2 :: ( Int, Int ) } myfunc = Thing { field1 ( _, x ) } = x but it doesn't work. That is, I want to match against the second item of the tuple which is the named field1. I'm not just trying to do this particular thing, but trying to figure out if some kind of general pattern matching can be done like this.
On 2009 Apr 7, at 3:30, Michael Mossey wrote:
I'm trying to do something like this:
data Thing = Thing { field1, field2 :: ( Int, Int ) }
myfunc = Thing { field1 ( _, x ) } = x
myfunc (Thing {field1 = (_,x)}) = x using record pattern matching
-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
On 7 Apr 2009, at 09:30, Michael Mossey wrote:
I'm trying to do something like this:
data Thing = Thing { field1, field2 :: ( Int, Int ) }
myfunc = Thing { field1 ( _, x ) } = x
but it doesn't work. That is, I want to match against the second item of the tuple which is the named field1. I'm not just trying to do this particular thing, but trying to figure out if some kind of general pattern matching can be done like this.
Firstly, you have an extra equals in there, secondly, in a pattern match constructions must go in parentheses, and finally, you're missing an equals inside the record: myFunc (Think {field1 = (_,x)}) = x Bob
participants (3)
-
Brandon S. Allbery KF8NH -
Michael Mossey -
Thomas Davie