Prelude> "foo" "bar"
<interactive>:3:1:
Couldn't match expected type ‘[Char] -> t’
with actual type ‘[Char]’
Relevant bindings include it :: t (bound at <interactive>:3:1)
The function ‘"foo"’ is applied to one argument,
but its type ‘[Char]’ has none
In the expression: "foo" "bar"
In an equation for ‘it’: it = "foo" "bar"
Prelude> 1 2
<interactive>:2:1:
Non type-variable argument in the constraint: Num (a -> t)
(Use FlexibleContexts to permit this)
When checking that ‘it’ has the inferred type
it :: forall a t. (Num a, Num (a -> t)) => t
> "foo" "bar"
-- TYPE MISMATCH --------------------------------------------- repl-temp-000.elm
You are giving an argument to something that is not a function!
3| "foo" "bar"
^^^^^
Maybe you forgot some parentheses? Or a comma?
> "foo" + "bar"
-- TYPE MISMATCH --------------------------------------------- repl-temp-000.elm
The left argument of (+) is causing a type mismatch.
3| "foo" + "bar"
^^^^^
(+) is expecting the left argument to be a:
number
But the left argument is:
String
Hint: To append strings in Elm, you need to use the (++) operator, not (+).
<http://package.elm-lang.org/packages/elm-lang/core/latest/Basics#++>The second error message, on the other hand, proves that the first one is a lucky accident.
Haskell is telling you 'you tried to apply a string literal to an argument as if it were a function, but it's not! It's a string literal. By the way, the string I'm talking about is "foo", which you tried to apply to "bar" in the expression "foo bar"'.
Yikes? It seems pretty helpful to me :)
Your second example is better, though.
That said, in a recent HN post somebody said that the latest version of GHC has better error messages, which I agree would be welcome, but I haven't tried it.