routines (
           mark_regions
           main_suffix
           consonant_pair
           other_suffix
)

externals ( stem )

integers ( p1 x )

groupings ( v s_ending )

stringescapes {}

/* special characters (in MS-DOS Latin I) */

stringdef ae   hex '91'
stringdef ao   hex '86'
stringdef o/   hex '9B'

define v 'aeiouy{ae}{ao}{o/}'

define s_ending  'bcdfghjlmnoprtvyz'

define mark_regions as (

    $p1 = limit

    test ( hop 3 setmark x )
    goto v  gopast non-v  setmark p1
    try ( $p1 < x  $p1 = x )
)

backwardmode (

    define main_suffix as (
        setlimit tomark p1 for ([substring])
        among(

            'a' 'e' 'ede' 'ande' 'ende' 'ane' 'ene' 'hetene' 'en' 'heten' 'ar'
            'er' 'heter' 'as' 'es' 'edes' 'endes' 'enes' 'hetenes' 'ens'
            'hetens' 'ers' 'ets' 'et' 'het' 'ast'
                (delete)
            's'
                (s_ending or ('k' non-v) delete)
            'erte' 'ert'
                (<-'er')
        )
    )

    define consonant_pair as (
        test (
            setlimit tomark p1 for ([substring])
            among(
                'dt' 'vt'
            )
        )
        next] delete
    )

    define other_suffix as (
        setlimit tomark p1 for ([substring])
        among(
            'leg' 'eleg' 'ig' 'eig' 'lig' 'elig' 'els' 'lov' 'elov' 'slov'
            'hetslov'
                (delete)
        )
    )
)

define stem as (

    do mark_regions
    backwards (
        do main_suffix
        do consonant_pair
        do other_suffix
    )
)