A function is also a type of value. When a function is used in arithmetic expressions, it is implicitly called with no arguments.

Yewslip> f = func(x) return x * 2 + 3

Yewslip> print f
func(x) return ((x * 2) + 3)

Yewslip> print f(3)
9

Yewslip> print f + 7
10