`syntax-rules`: accept ellipsis with improper lists -- enhances pattern-matching (brings easy path to incorporate at least two SRFIs)

[jpellegrini]

Hi @egallesio !

The reference implementations of SRFIs 227 (optional lambda) and 232 (currying) use ellipsis patterns in improper lists, and STklos currently doesn't handle those. This patch fixes that. Maybe this also allows us to bring the reference implementation of SRFI 197 (pipeline operators), butI didn't test that.

See the description:

mbe:matches-pattern? and mbe:get-bindings did not account for the presence of an ellipsis pattern in an improper list, as in (a b ... c . d). It would call length on the list tail after the ellipsis, which would signal an error.

So, we:

• Create split-improper-tail, which splits the list into lst-CDR and everything but it. (split-improper-tail '()) => values '(), '() (split-improper-tail '(1 2 3)) => values '(), '(1 2 3) (split-improper-tail '(1 2 . 3)) => values '(3), '(1 2)

• Change mbe:matches-pattern? and mbe:get-bindings to use split-improper-tail

• Since we were there, document those procedures a bit. :)

• And, of course, include some tests...

[jpellegrini]

The reference implementations of SRFIs 227 (optional lambda) and 232 (currying) use ellipsis patterns in improper lists,

Ha ha! I just realized you already implemented SRFI 227. Anyway, 232 is ready!

[egallesio]

Great!!! Thanks @jpellegrini. I'm merging it immediately.