Parentheses in Haskell aren’t really related to function application, they are only for grouping. It makes more sense if you avoid using them unless strictly necessary. In Haskell instead of `f(g(x))` we would write `f (g x)`, and instead of `f(x,g(y),z)` we would write `f x (g y) z`. You could use more parentheses but it would be more confusing, such as `(f)(x)(g(y))(z)`. On Sun, Jun 28, 2020 at 05:50 Josh Friedlander wrote:

Thanks Francesco, that works. I don't quite understand what the issue was, though. Specifically: - Did the parentheses around (xs) hurt, or were they just redundant? - Wouldn't the parentheses around (head ...) be binding it as an argument to whatever comes before (in this case, 3)?

On Sun, 28 Jun 2020 at 14:47, Francesco Ariis wrote:

...

Hello Josh

Il 28 giugno 2020 alle 14:36 Josh Friedlander ha scritto:

...

I want to create a log parser like this:

module LogAnalysis where import Log

parseMessage :: String -> LogMessage parseMessage xs | length(words(xs)) < 3 = Unknown xs | notElem(head(words(xs)) ["I", "E", "W"]) = Unknown xs | otherwise = LogMessage Info 3 head(words(xs))

But GHC gives me "• Couldn't match type ‘[a0] -> a0’ with ‘[Char]’ Expected type: String Actual type: [a0] -> a0"

I suspect `LogMessage Info 3 head(words(xs))` is the problem. This is the same as writing

LogMessage Info 3 head (words xs)

keeping in mind how whitespace and parentheses work in Haskell. You probably want

LogMessage Info 3 (head (words xs))

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