[Haskell-cafe] Prelude.head: empty list

Chris Wong lambda.fairy at gmail.com
Sat Mar 12 03:28:58 UTC 2016

On Sat, Mar 12, 2016 at 8:07 AM, Jonas Scholl
<anselm.scholl at tu-harburg.de> wrote:
> You mean like this?
>   default-extensions:  CPP
>   cpp-options:
> -Dhead=(foldr(const)(error("head:\x20\x65mpty\x20list\x20in\x20"++__FILE__++":"++show(__LINE__))).(take$1))

That's pretty cool!

By the way: can the (take$1) be removed? foldr should be lazy enough already.

Chris Wong (https://lambda.xyz)

"I had not the vaguest idea what this meant and when I could not
remember the words, my tutor threw the book at my head, which did not
stimulate my intellect in any way." -- Bertrand Russell

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