How can I get the position where error was called?

Question

I am looking for something to replace loch (and its preprocessor) since it doesn\'t compile with ghc 7.

Specifically, if error is called then I would l

Answer 1

A quick-n-dirty workaround is the assert function from Control.Exception. However, it's a little clunkier than error.

Warning: All asserts will be silently ignored if you compile with optimizations (ghc -O1, -O2, etc.).

Example:

import Control.Exception

main = do
    print (42 + (assert True  17)) -- adds 42 and 17
    print (42 + (assert False 21)) -- crashes

Output:

59
test.hs: /tmp/test.hs:5:18-23: Assertion failed

Note the line number "5" in the output.

You could use trace from Debug.Trace to add an error message:

    print (42 + (trace "omg error" $ assert False 21))