On Sunday, November 20, 2016 at 2:05:32 PM UTC+1, Luis Sanjuán wrote: > On Tuesday, November 15, 2016 at 5:30:54 PM UTC+1, Brian Adkins wrote: > > I'm working on a simple chess engine in Racket as a learning exercise. I > > initially wrote this function: > > > > (define (valid-queen-moves board idx is-opposite-color?) > > (append (valid-bishop-moves board idx is-opposite-color?) > > (valid-rook-moves board idx is-opposite-color?))) > > > > I didn't like the redundancy, so I re-wrote as: > > > > (define (valid-queen-moves board idx is-opposite-color?) > > (append-map (λ (f) (apply f (list board idx is-opposite-color?))) > > (list valid-bishop-moves valid-rook-moves))) > > > > I thought that was still ugly, so I re-wrote as: > > > > (define (valid-queen-moves . args) > > (append-map (λ (f) (apply f args)) > > (list valid-bishop-moves valid-rook-moves))) > > > > And it was at this point that I finally though, "This has to be a solved > > problem already", but my initial searching turned up empty, so I wrote this: > > > > (define (unionify . functions) > > (λ args (append-map (λ (f) (apply f args)) functions))) > > > > (define valid-queen-moves (unionify valid-bishop-moves valid-rook-moves)) > > > > unionify is a *terrible* name, but my question is whether this higher order > > function already exists in the standard Racket library? I came close to > > writing flat-map before I found append-map, so I don't want to reinvent > > another wheel needlessly. > > > > Brian > > > Probably useless for your use case due to performance penalty, but in other > cases `conjoin` might do the work: > > https://docs.racket-lang.org/reference/procedures.html?q=conjoin#%28def._%28%28lib._racket%2Ffunction..rkt%29._conjoin%29%29
I meant `disjoin` since you need to or-ing rather than and-ing. The idea is to pass the `disjoin`/`conjoin` construct as the first argument to `filter` over all possible moves. -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
