this is a variant proposed by Gabriele (note the usage of the /only
refinement):
collect: closure [
{Collects values, returning them as a series.}
[throw]
emit [word!] "Word used to collect values"
block [block!] "Block to evaluate"
/into dest [series!] "Where to append results"
] [
; Create a new context containing just one word (the EMIT
; argument) and set the 'emit word to refer to the new context
; word. Note the care taken to suppress possible conflicts and
; undesired evaluations.
emit: reduce [emit]
emit: first use emit reduce [emit]
dest: any [:dest []]
; make the function used to collect values.
set emit func [value [any-type!] /only] [
either only [insert/only tail :dest get/any 'value] [
insert tail :dest get/any 'value
]
get/any 'value
]
do bind/copy block emit
head :dest
]
probe collect 'emit [emit [1 2] emit/only [3 4]] ; == [1 2 [3 4]]
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