Question

If I have a function like so:

func:: Arg1->Arg2->String

and Arg1 has a constructor like:

data Arg1 = something1 something2 something3

I want to pattern match on one of the Arg1 constructors within func (below I have pattern matched on “Val1”):

func:: Arg1->Arg2->String
func (a b Val1) e = "Something"

but it keeps saying I have a problem with parsing symbol ‘a’

The variables in the brackets just represent Arg1??? “e” is the Arg2 parameter.

EDIT: This seems to work:

func:: Arg1-> Arg2-> String
func (A b Val1) e = "Something"

but I cannot pattern-match on A because i’m not bothered about that value.

EDIT2: Seems like I need to do:

data Arg1 = Arg1 something1 something2 something3

for it to work?!?!

Answer 1

You have to pattern match on the constructor as well.
You also forgot to specify the constructor for Arg1.

func :: Arg1 -> Arg2 -> String
func (Arg1 a b Val1 d) e = "Foobar"