foo

#!/usr/bin/env perl6

use Grammar::ErrorReporting;

use Grammar::Tracer;
grammar Ingredient::Grammar does Grammar::ErrorReporting {
    token TOP { <ingredient> }

    token ingredient {
        <number>?
        <.ws>?
        <unit>?
        <.ws>?
        <items>
        <.ws>?
        <alternative>?
        <.ws>?
        <prep>?
    }
    token number { <:N>+ || <.error('Not a number')> }

    proto token unit {*}
    token unit:sym<g> { 'g' }
    token unit:sym<kg> { 'kg' }
    token unit:sym<l> { 'l' }
    token unit:sym<ml> { 'ml' }
    token unit:sym<tbsp> { 'tbsp' }
    token unit:sym<tsp> { 'tsp' }

    rule items { .+ [<?before or> | <?before ','>] || .+ }
    rule alternative { 'or' <items> }
    rule prep {',' <items>}
}


say Ingredient::Grammar.parse("23 tbsp salt, 3 cups flour");

output

/home/duff/tmp
➤ ./foo
TOP
|  ingredient
|  |  number
|  |  * MATCH "23"
|  |  unit
|  |  |  unit:sym<tbsp>
|  |  |  * MATCH "tbsp"
|  |  * MATCH "tbsp"
|  |  items
|  |  * MATCH "salt"
|  |  alternative
|  |  * FAIL
|  |  prep
|  |  |  items
|  |  |  * MATCH "3 cups flour"
|  |  * MATCH ", 3 cups flour"
|  * MATCH "23 tbsp salt, 3 cups flour"
* MATCH "23 tbsp salt, 3 cups flour"
｢23 tbsp salt, 3 cups flour｣
 ingredient => ｢23 tbsp salt, 3 cups flour｣
  number => ｢23｣
  unit => ｢tbsp｣
  items => ｢salt｣
  prep => ｢, 3 cups flour｣
   items => ｢3 cups flour｣
/home/duff/tmp
➤ perl6 -v
This is Rakudo version 2017.08-33-g74ca5ce built on MoarVM version 2017.08.1-19-g151a256
implementing Perl 6.c.