How to make a right-associative infix operator?

scala associative infix-notation
Petr picture Petr · Mar 13, 2013 · Viewed 7.4k times · Source

I have an associative operation >>. The problem is that its cost linearly depends on the size of its left operand. So an expression formed by a sequence of n applications of >> like

a >> a >> a >> a >> a >> ... >> a

it has quadratic cost in terms of n, because by default infix operators are left-associative. How to make it right-associative so that the cost of such an expression is kept linear in terms of n?

Answer

Petr picture Petr · Mar 13, 2013

I found a solution. Scala reference says in section 6.12.3 Infix Operations:

The associativity of an operator is determined by the operator’s last character. Operators ending in a colon ‘:’ are right-associative. All other operators are left-associative.

Therefore it was enough to rename >> to >>:.

It took me some time to realize that while a >> b is desugared into a.>>(b), a >>: b is desugared into b.>>:(a). So I had to define >>: as

def >>:(x: T): T = x >> this

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