GHC error message on type mismatch

Daniel Trstenjak daniel.trstenjak at
Thu Nov 7 11:52:34 UTC 2013


I don't know if I'm the only one struggeling with this GHC error message
on type mismatches or it's because I'm not a full time Haskeller, or
because I'm not a native english speaker.

Couldn't match type `A' with `B´
    Expected type: B
      Actual type: A

My problem is with 'Expected' and 'Actual', that I'm often unsure if
the compiler is "expecting" something or if I'm the expecting one
and the same goes for "actual".

I know that the compiler is the expecting one and that I'm given the
actual thing, but it's quite often that I'm looking at this error
and have to repeat this reasoning.

It's strange, because normaly I can memorize such things quite good,
but this one bothers me.

Perhaps it would be easier for myself if 'Actual type' would be called
e.g. 'Given type', I don't know, that just one of the two has a less
generic meaning.


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