# "Potato, Egg, Red meat & Lard Cookbook",
# T. Omnicient Rash & N. Hot Ignorant-Kant
# O'Besity & Associates

use Parse::RecDescent;

$grammar =
q{
    Recipe: Step(s)

    Step:
        Verb Object Clause(s?)
            { print "$item[1]\n" }
          | <resync:[ ]{2}>

    Verb:
        'boil'
          | 'peel'
          | 'mix'
          | 'melt'
          | 'fry'
          | 'steam'
          | 'marinate'
          | 'sprinkle'
          | 'is'
          | 'are'
          | 'has'

    Object:
        IngredientQualifier(s) Ingredient
          | ReferenceQualifier(s) Ingredient
          | Reference

    Clause:
            SubordinateClause
              | CoordinateClause

    SubordinateClause:
        'until' State
          | 'while' State
          | 'for' Time

    CoordinateClause:
        /and( then)?/ Step
          | /or/ Step

    State:
        Object Verb Adjective
          | Adjective

    Time:
        Number TimeUnit

    TimeUnit:
        /hours?/
        /minutes?/
        /seconds?/

    QuantityUnit:
        /lbs?/


    Object:
        ReferenceQualifier Ingredient
          | Reference

    Reference:
        'they'
          | 'it'
          | 'them'

    Ingredient:
        'potatoes'
          | 'lard'
          | 'olive oil'
          | 'sugar'
          | 'bacon fat'
          | 'butter'
          | 'salt'
          | 'vinegar'

    IngredientQualifier:
        Amount
          | Number
          | 'a'
          | 'some'
          | 'large'
          | 'small'

    Amount: Number QuantityUnit

    ReferenceQualifier:
            'the'
          | 'those'
          | 'each'
          | 'half the'

    Number:
        /[1-9][0-9]*/
          | /one|two|three|four|five|six|seven|eight|nine/
          | 'a dozen'

    Adjective:
        'soft'
          | 'tender'
          | 'done'
          | 'charred'
          | 'grey'

};

$parse = new Parse::RecDescent ($grammar);

$/ = "\n\n";
while (<DATA>)
{
    if($ingredients = $parse->Recipe(lc $_))
    {
        print "$ingredients\n$_";
    }
}

__DATA__
Boil six large potatoes until they are grey and then marinate them
for at least two hours in a mixture of lard, olive oil, raw
sugar, and sea-salt.  In a deep-fryer melt 2 lbs of bacon fat and
bring to the boil.  Fry the marinated potatoes for 7 minutes, or
until they are nicely charred.  Serve with lashings of butter.
Sprinkle with salt and vinegar to taste.