I was working with the minikanren library for Racket, but wanted to use the "disj" and "conj" operators. I want to be able to more explicitly declare whether I am using disj or conj for the sake of legibility rather than have to parse through a conde expression, especially once the expressions become more complicated. I copied the source from "The Reasoned Schemer":
(define (append∞ s∞ t∞)
(cond
((null? s∞) t∞)
((pair? s∞)
(cons (car s∞)
(append∞ (cdr s∞) t∞)))
(else (λ ()
(append∞ t∞ (s∞))))))
(define (disj2 g1 g2)
(λ (s)
(append∞ (g1 s) (g2 s))))
(define-syntax disj
(syntax-rules ()
[(disj) '()]
[(disj g) g]
[(disj g0 g ...) (disj2 g0 (disj g ...))]))
This works properly with the first two cases
> (run* (x) (disj (== 'foo x)))
'(foo)
but only returns the first result when using more than one goal:
> (run* (x) (disj (== 'foo x) (== 'bar x) (== 'foobar x)))
'(foo)
Why is this?
Hrmph. I can't seem to reproduce that behavior.
When I clone the TRS/2e repo, add both
#lang racket
(provide (all-defined-out))
to the top of trs2-impl.scm, run that file, and then try your test program I see the expected result:
;
; Welcome to Racket v7.9.0.3 [cs].
;
trs2-impl.scm> (run* (x) (disj (== 'foo x) (== 'bar x) (== 'foobar x)))
'((foo) (bar) (foobar))
Do you see different behavior? If so, then we could look deeper. Do you know which version of Racket you're using? I don't think that will matter, but just in case.