capture ( group match -- slice/f )
Regular expressions » Regular expression capture groups

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Vocabulary
regexp

Inputs

group	a group number or name
match	a regexp-match

Outputs

slice/f

a slice or f

Word description
Returns a group by its zero-based number or string name. Group zero is the whole match. Returns f for a group that did not participate.

Errors
Throws unknown-capture-group if the group number or name does not exist.

Definition

USING: accessors assocs kernel math regexp.captures sequences
strings ;

IN: regexp

:: capture ( group match -- slice/f )
    group string? [
        group match names>> at
        [ group unknown-capture-group ] unless*
    ] [ group ] if :> index index integer?
    [ index 0 >= index match groups>> length < and ] [ f ] if
    [ index match groups>> nth ] [ group unknown-capture-group ]
    if ;