Question

initials :: String -> String -> String
initials firstname lastname = [f] ++ ". " ++ [l] ++ "."
    where (f:_) = firstname
          (l:_) = lastname 

For this code. I got error

parse error on input `='

Why?

Answer 1

You use a tab character before the where keyword. To GHC it looks like this:

␉       where␠(f:_)␠=␠firstname
␠␠␠␠␠␠␠␠␠(l:_)␠=␠lastname 

So, GHC thinks that the first line in the where block starts at column 14 (tab counts for 8 columns iirc) while the second line starts at column 9, which causes the error.

You should use a good text editor that converts tabs into 4 spaces for you.