head of empty list returns a

[sudarshanchoubey]

head []
returns a

[Ingo60]

No, it doesn't.

When the repl finds that it cannot show the result of the expression, it just prints the type instead of the expression.

For example:

frege> []
[a]

If, OTOH it knows how the result can be printed, it actually evaluates the expression:

frege> :t head ([] :: [Int])
Int

frege> head ([] :: [Int])
frege.runtime.Undefined: head []

frege> head [ i | i <- [1..10], i > 50 ]
frege.runtime.Undefined: head []

frege> 

I think this is better to see in the online repl, where there are colors.

[sudarshanchoubey]

Does a here mean Any?

[Ingo60]

Yes, sort of.