Expressions
The =~ and !~ operators can be used to check against regular expressions.
The expression a =~ b is true if a matches b, while a !~ b is true if a does not match b.
Just as with comparison operators, these operators may be used as unary versions to define a set of strings.
regexp.cue:
a: "foo bar" =~ "foo [a-z]{3}"
b: "maze" !~ "^[a-z]{3}$"
c: =~"^[a-z]{3}$" // any string with lowercase ASCII of length 3
d: c
d: "foo"
e: c
e: "foo bar"
$ cue eval -i regexp.cue
a: true
b: true
c: =~"^[a-z]{3}$"
d: "foo"
e: _|_ // invalid value "foo bar" (does not match =~"^[a-z]{3}$")