Hi,
If I define the follwoing functions:
car (x:_) = x
car [] = []
cdr (_:xs) = xs
cdr [] = []
and try to apply them to some list, such as
car [1,2,3]
I get this odd error:
interactive:1:9:
No instance for (Num [a])
arising from the literal `3' at interactive:1:9
Possible fix:
Fernando Rodriguez writes:
car (x:_) = x
car [] = []
...
and try to apply them to some list, such as
car [1,2,3]
I get this odd error:
No instance for (Num [a])
arising from the literal `3' ...
The error is really a bit cryptic (who cares, Nums or whatever...)
but the error is
On 13 Jan 2008, [EMAIL PROTECTED] wrote:
If I define the follwoing functions:
car (x:_) = x
car [] = []
This won't typecheck. It helps to add a type signature
car :: [a] - a
The first element of an empty list is undefined, so you can do what
Prelude.head does and write:
car [] =
On Jan 13, 2008 7:55 AM, Fernando Rodriguez [EMAIL PROTECTED] wrote:
If I define the follwoing functions:
car (x:_) = x
car [] = []
What's the type signature for that function?
Cheers!
--Tom Phoenix
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Haskell-Cafe mailing list
On Jan 13, 2008 2:07 PM, Tom Phoenix [EMAIL PROTECTED] wrote:
On Jan 13, 2008 7:55 AM, Fernando Rodriguez [EMAIL PROTECTED] wrote:
If I define the follwoing functions:
car (x:_) = x
car [] = []
What's the type signature for that function?
car :: [[a]] - [a]
--
Felipe.
Jed Brown writes:
On 13 Jan 2008, [EMAIL PROTECTED] wrote:
If I define the follwoing functions:
car (x:_) = x
car [] = []
This won't typecheck. It helps to add a type signature
car :: [a] - a
Good will, wrong diagnosis. This WILL check.
car :: forall a. [[a]] - [a]
J.
