Fleshing out a model for a COLLECT/KEEP in Parse based on correctness.

buckets.reb

Rebol [
	Title: "Fleshing out a model for a COLLECT/KEEP in Parse based on correctness"
	Date: 26-Apr-2015
	Author: "Christopher Ross-Gill"
]

buckets: []
new-branch: quote (insert/only buckets bucket: copy [])
fold-branch: quote (bucket: buckets/2 append bucket take buckets)
kill-failed-branch: quote (remove buckets)

if probe parse [a b c][
	new-branch
	'a (append bucket 'a) ; keep 'a
	[
		new-branch
		'b (append bucket 'b) ; keep 'b
		'd (append bucket 'd) ; keep 'd

		; successful end of rule
		fold-branch
		|
		; rule failed, so
		kill-failed-branch
		new-branch
		'b (append bucket 'b) ; keep 'b
		'c (append bucket 'c) ; keep 'c

		; successful end of rule
		fold-branch
	]
][
	probe bucket
]

original-buckets.reb

Rebol [
	Title: "Fleshing out a model for a COLLECT/KEEP in Parse based on correctness"
	Date: 26-Apr-2015
	Author: "Christopher Ross-Gill"
]

buckets: []

if probe parse [a b c][
	(insert/only buckets bucket: copy [])
	'a (append bucket 'a) ; keep 'a
	[
		(insert/only buckets bucket: copy [])
		'b (append bucket 'b) ; keep 'b
		'd (append bucket 'd) ; keep 'd

		; successful end of rule
		(bucket: buckets/2 append bucket take buckets)
		|
		; rule failed, so
		(remove buckets)
		(insert/only buckets bucket: copy [])
		'b (append bucket 'b) ; keep 'b
		'c (append bucket 'c) ; keep 'c

		; successful end of rule
		(bucket: buckets/2 append bucket take buckets)
	]
][
	probe bucket
]