Haskell - too few arguments

Question

I want to write a Haskell program that calculates the sum of numbers between 2 given numbers. I have the following code:

sumInt :: Int -> Int -> Int
sumInt x y
   | x > y = 0
   | otherwise = x + sumInt x+1 y

But when I compile it I get the following error:

SumInt is applied to too few arguments.

I don't understand what I'm doing wrong. Any ideas?

Why was this downvoted? +1 even just to negate, this question is definitely within the scope of SO (and it's a good one too). — MasterMastic
– MasterMastic, Commented Nov 26, 2014 at 18:03

Louis Wasserman · Accepted Answer · 2014-11-26 18:42:55Z

7

You need parentheses around x+1:

| otherwise = x + sumInt (x + 1) y

The reason is that function application binds more tightly than operators, so whenever you see

f x <> y

This is always parsed as

(f x) <> y

and never as

f (x <> y)

edited Nov 26, 2014 at 18:42

Louis Wasserman

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answered Nov 26, 2014 at 17:33

bheklilr

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2 Comments

MasterMastic Over a year ago

How did the compiler try to read it when it reported the error? can you demonstrate using parentheses?

bheklilr Over a year ago

@MasterMastic The compiler would have read this particular expression as x + (sumInt x) + (1 y). Due to polymorphism of numeric literals, 1 y actually typechecks, it just doesn't have an instance of Num available that is a function. The error came from sumInt x, which is said to have type Int, with x being known as Int, so the first error it encounters is a mismatch between Int -> Int and Int, for which it suggests you don't have enough parameters.

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