Parslet Alternatives Not parsing whole string

[darshan-patel]

@kschiess

require 'parslet'
require 'parslet/convenience'

class Lines < Parslet::Parser
    rule(:open_tag) {str('[')}
    rule(:close_tag) {str(']')}
    rule(:data) {str('name') | str('name_id') }
    rule(:text) { open_tag >> data >> close_tag }
    root :text
end

begin
    p Lines.new.parse("[name_id]")    <---- It throws error
rescue Parslet::ParseFailed => failure
    Lines.new.parse_with_debug("[name_id]")
end

Is there any alternative for this problem?

[rathrio]

@darshan-patel does it work when you try to match the longer string first? e.g.

rule(:data) { str('name_id') | str('name') }

[kschiess]

require 'parslet'
require 'parslet/convenience'

class Lines < Parslet::Parser
    rule(:open_tag) {str('[')}
    rule(:close_tag) {str(']')}
    rule(:data) { str('name_id') | str('name') }
    rule(:text) { open_tag >> data >> close_tag }
    root :text
end

begin
    p Lines.new.parse("[name_id]")   # <---- It throws error
rescue Parslet::ParseFailed => failure
    Lines.new.parse_with_debug("[name_id]")
end

When using top-down parsers (and parslet can be thought of as one, in simplification) you will always have to match the longer alternative first, failing that you'll match the shorter one. The problem is the common substring of your 'data' token.