Scala Higher Order Functions and Implicit Typing

Question

I recently started working with Functional Programming in Scala and am learning Scala in the process. While attempting one of the Chapter 2 exercises to define a function that curries another function, I ran into this:

If I write

def curry[A,B,C](f: (A,B) => C): A => B => C = a: A => b: B => f(a, b)

then I get

Chapter2.scala:49: error: ';' expected but ':' found.
a: A => b: B => f(a, b)
_______^
one error found

BUT if I write

def curry[A,B,C](f: (A,B) => C): A => B => C = a => b => f(a, b)

then it compiles fine, with no warnings, and works. What's the difference?

Well the difference is obviously that the first example is not syntactically correct. — SamTebbs33
– SamTebbs33, Commented Aug 23, 2016 at 16:04

jtitusj · Accepted Answer · 2016-08-23 16:33:26Z

4

You just need to enclose your variables in parentheses. In your example, you can write:

def curry[A,B,C](f: (A,B) => C): A => B => C = (a: A) => (b: B) => f(a, b)

answered Aug 23, 2016 at 16:33

jtitusj

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2 Comments

D. Ben Knoble Over a year ago

This is a quirk to me; is there an explicit reason why?

Alexey Romanov Over a year ago

In general, parentheses are required in a: A => ... form; they are only allowed to be omitted when it is the last expression in a block. See scala-lang.org/files/archive/spec/2.11/….

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