You mean like this? default-extensions: CPP cpp-options: -Dhead=(foldr(const)(error("head:\x20\x65mpty\x20list\x20in\x20"++__FILE__++":"++show(__LINE__))).(take$1)) Yes, it is a little bit ugly as I am unable to convince cabal to skip the spaces, so I just avoided them. And build an ugly inline-definition of head. Maybe having a head' function taking a line number and the file would help :) But it should work, if it is not too much broken my my mail-client. The define should be on one long line. On 03/11/2016 07:26 PM, Francesco Ariis wrote:
On Fri, Mar 11, 2016 at 04:56:57PM +0100, Han Joosten wrote:
In a rather large program I made some changes, and now I get the runtime error:
ampersand.exe: Prelude.head: empty list
Of course I know that head is partial, and should be used with care. It is used many times (we have 100+ modules in the program). Is there an elegant way to get some information about where the specific call to head is being made?
Thanks!
I scanned previous replies and didn't see it mentioned, maybe you can abuse C preprocessor to shadow `head` and insert a __LINE__ on pattern matching []? _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe