Association of pure functions

Question

I've encountered confusing behavior of Association when I try to use it for storing pure functions.

For example:

as = <|"1" -> # + 1 &|>

Association["1" -> #1 + 1 &]

Strangely:

AssociationQ@as

False

and it is not possible to extract the value by the key:

as["1"]

Association["1" -> #1 + 1 &]["1"]

Is this the intended behavior?

P.S. Wrapping pure functions in Hold[] solves the problem, but I'm still curious why doesn't Association work without it.

I have closed this as a duplicate as the origin of the unexpected behavior is the same: the grouping of the & operator. Please also see: (30425) — Mr.Wizard, Oct 07 '14 at 20:00

score 8 · Accepted Answer · answered Oct 07 '14 at 19:56

8

Just add the parentheses

as = <|"1" -> (# + 1 &)|>
(* <|"1" -> (#1 + 1 &)|> *)

AssociationQ@as
(* True *)

Rule (->) has lower precedence then &.

answered Oct 07 '14 at 19:56

ybeltukov

1 Answers1