Parse error on input '='

Question

I keep getting this message, what am I doing wrong?

quadrant :: Float -> Float -> Quadrant
quadrant x y
    |x = 0 && y = 0 = Origin
    |x > 0 && y = 0 = X_ Axis_Positive
    |x > 0 && y > 0 = Quadrant_1
    |x = 0 && y > 0 = Y_ Axis_Positive
    |x < 0 && y > 0 = Quadrant_2
    |x < 0 && y = 0 = X_ Axis_Negative
    |x < 0 && y < 0 = Quadrant_3
    |x = 0 && y < 0 = Y_ Axis_Negative
    |x > 0 && y < 0 = Quadrant_4
    |otherwise = error "Program error: Non-Exhaustive guards in function: quadrant"

Mark H · Accepted Answer · 2014-03-12 21:43:53Z

7

The operator to test for equality is ==, where = is part of the language grammar.

edited Mar 12, 2014 at 21:43

answered Mar 12, 2014 at 21:33

Mark H

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4 Comments

Mark H Over a year ago

(==) isn't part of the language syntax but part of the Prelude. It's defined with infix 4 ==; (==) :: (Eq a) => a -> a -> Bool

user2864740 Over a year ago

I'm not disagreeing with the fundamental answer - but I was hoping for refinement on the last few words, and possibly a reference (e.g. as to "what" = is).

Mark H Over a year ago

Semantics. It's probably more accurate to say grammar. I'm referring to the rules of the language structure, and not the whole language itself.

David Young Over a year ago

@user2864740 (==) is a type class method that is defined in the Haskell standard library and = is a fundamental part of the Haskell language itself. = cannot be broken down further, in the same sense as { and } in C/C++/C#/Java/etc and : in Python.

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