[Haskell-cafe] Access to list

[Jed Brown]

On 13 Jan 2008, frr149 at easyjob.net 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 [] = undefined

> cdr (_:xs) = xs
> cdr [] = []

This is entirely valid, but may not be what you want.
  cdr [] = undefined        -- like Prelude.tail

Jed
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