Matching any child with NodePattern

[marcandre]

From @Drenmi :

there's a long standing request to add an "any child" matcher. This would be especially helpful when matching on hashes. Consider:

ruby-parse -e '{ foo: 1, bar: 2 }'

(hash
  (pair
    (sym :foo)
    (int 1))
  (pair
    (sym :bar)
    (int 2)))

We may be interested in hashes that have a foo: 1 pair, but the pairs can appear in any order, so we can't reliably match that in a pattern. 🙂

What is needed is a suggested extension to the syntax, and the actual implementation.

Suggested syntax extension would be <...> as it seems the easiest remaining "brackety" symbol left.

Simple:

(hash <(pair (sym :foo) (int 1)) (pair (sym :bar) (int 2))>)

This would match {bar: 2, foo: 1} and {foo: 1, bar: 2} but nothing else. To match hashes containing these two value-key pairs, use ...:

Ellipsis:

(hash <(pair (sym :foo) (int 1)) ...>)

This would match any literal hash with a foo: 1 key-value pair. Ellipsis must be at end of <> sequence.

Note: Patterns are attempted to be matched in the order given. <(pair _ (int 1)) (pair (sym :foo) _)> would match {bar: 1, foo: 1} but not {foo: 1, bar: 1}. Captures are always returned in the order of the pattern.

Comments?

[marcandre]

Description edited to match #6965