gistfile1.txt

% year digits
#vars $yd1: 0 1 2 3 4 5 6 7 8 9 .
#vars $yd2: 0 1 2 3 4 5 6 7 8 9 .
#vars $yd3: 0 1 2 3 4 5 6 7 8 9 .
#vars $yd4: 0 1 2 3 4 5 6 7 8 9 .

#vars $d01: 0 1 .
#vars $d02: 0 1 2 .
#vars $d12:   1 2 .
#vars $d09: 0 1 2 3 4 5 6 7 8 9 .
#vars $d19:   1 2 3 4 5 6 7 8 9 .


ISODATE:

	% 'true' if the first token looks like ISO 8601 date specification
	% (YYYY-MM-DD or some valid prefix) with *very* crude checking for
	% date ranges (months 01-12, days <= 31)
	%
	% 'false' otherwise
	<is-date $$any> == <-is-date year Explode:<$$any .>>
	<is-date> == false

	% year (four digits)
	<-is-date year $yd1 $yd2 $yd3 $yd4> == <-is-date end-or month>
	% month (dash 01 to 12)
	<-is-date month '-'> == <-is-date mm>
	<-is-date mm 0 $d19> == <-is-date end-or day>
	<-is-date mm 1 $d02> == <-is-date end-or day>
	% day (dash 01 to 31)
	<-is-date day '-'> == <-is-date dd>
	<-is-date dd 0    $d19> == <-is-date end-or fail>
	<-is-date dd $d12 $d09> == <-is-date end-or fail>
	<-is-date dd 3    $d01> == <-is-date end-or fail>
	% end of string or trigger next is-date parser
	<-is-date end-or $$arg $$any> == <-is-date $$arg $$any>
	<-is-date end-or $$arg> == true
	% fail
	<-is-date> == false

.