Type information loss

[int-index]

This code:

var
 x: integer;
begin
 readln(x);
 writeln(x);
end.

translates into this code:

main :: IO ()
main = void (readLn >>= print)

Type information about x is lost, so the resulting code is ambigious and doesn't compile. This is due to excessive optimizations that don't always preserve type information.