lua speedwalk parser

function parse_cmud_sws( _, _, wildcards )
--
    lpeg = require( "lpeg" )

    world.SetVariable ( "sws", "" )

    local sw = wildcards[1] or ""

    local C, Cc, Cf, P, V, match = lpeg.C, lpeg.Cc, lpeg.Cf, lpeg.P, lpeg.V, lpeg.match

    local directions, portal, sw_e, sw_s, walk = V( 'directions' ), V( 'portal' ), V( 'sw_e' ), V( 'sw_s' ), V( 'walk' )

    local sep = ";"

    local run = function( sw ) if sw:len() > 1 then sw = "run "..sw end return sw end

    local fold = function( walk, sw )
        if walk:len() == 0 then return sw end
        if sw:len() == 0 then return walk end
        return walk..sep..sw
    end

    local speedwalk = P {                                                                   -- grammar for path decoding.
                          'speedwalk',                                                      -- starting symbol name.
                          sw_e       = P(sep),                                              -- end-of-speedwalk   marker.
                          sw_s       = P('.'),                                              -- start-of-speedwalk marker.
                          directions = C((1 - sw_e)^0),                                     -- speedwalk string capture.
                          portal     = P('(' * C((1 - P(')'))^1) * ')')^0,                  -- custom exit command capture.
                          walk       = sw_s * portal * (directions / run) * sw_e^-1,        -- speedwalk iteration element.
                          speedwalk  = Cf(Cc("") * walk^0, fold)                            -- complete speedwalk search pattern.
                        } * -1                                                              -- end-of-input marker.
--
    world.SetVariable ( "sws", match( speedwalk, sw ) )

    return
--
end