//
// Simplified "Kennel story".
// `steps` should be provided externally.
// steps=11111 will produce a 50,000 word novel.
//

Goal ::=
    <. dx = 1 .> <. x = 0 .> <. a = 0 .> <. lx = 1 .>
    {
        DogMove<x, dx>
        <. x += dx .>
        DogTurnAround<x, dx, lx>
        <. a += 1 .>
    } <. a > steps .> <. x = 0 .>
    ;
DogMove<x, dx> ::=
      <. dx > 0 .> DogForth<x> #10
    | <. dx < 0 .> DogBack<x> #10
    ;
DogForth<x> ::=
      <. x < 1 .> "The dog ran away."
    | <. x > 0 .> "The dog ran further away."
    ;
DogBack<x> ::=
      <. x < 2 .> "The dog came back home."
    | <. x > 1 .> "The dog journeyed back."
    ;
DogTurnAround<x, dx, lx> ::=
      <. x > lx .> <. dx -= 2 .> <. lx += 1 .>
    | <. x < 1 .> <. dx += 2 .>
    | <. x >= 1 .> <. x <= lx .>
    ;