haskell getting parse error on input `->'

Question

I am using ghci compiler with version 7.8.3 on windows 7. I am getting error message showing parse error on input `->'. I have the following code for lambda expression in haskell.

add =\x y -> x+y

Note that =\ is an operator. Since you want to assign a lambda expression to the name add, you need a space: = \ . — Code-Apprentice
– Code-Apprentice, Commented Nov 1, 2014 at 18:51

that other guy · Accepted Answer · 2014-11-01 20:48:32Z

5

When defining a function interactively in ghci, you have to bind it using a let like this:

let add = \x y -> x + y

edited Nov 1, 2014 at 20:48

that other guy

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answered Nov 1, 2014 at 16:04

ThreeFx

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2 Comments

Carcigenicate Over a year ago

Not if it's globally stated function. If that is the case though, it should just be written in sugared form add x y = x + y, or just add = (+).

Ørjan Johansen Over a year ago

Also, the = and \ must be separated by space like here, because =\ is a legal operator name.

Ørjan Johansen · Accepted Answer · 2014-11-02 04:00:05Z

2

I just wrote:

add = \x y -> x + y

main = do
    print $ add 1 2

and it compiled and output 3.

Unless your intent is to practice unsugared code though, I would write it out as:

add x y = x + y

Or

add = (+)

which is "point-free" form.

edited Nov 2, 2014 at 4:00

Ørjan Johansen

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answered Nov 1, 2014 at 18:18

Carcigenicate

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