Problem with Reasoned Schemer 2nd ed's conj2 / append-map-inf in Racket

[Jeff Ward]

Another person has posted about trouble using the Reasoned Schemer 2nd ed code in Racket, but I thought I would add some specifics:

My trouble starts in Chapter 1, Frame 50, where conj2 is used. conj2 is not defined in the installed files, so I typed in the definition of conj2 and everything that it depends on, using the definitions provided in Chapter 10. The error that I get says:
car: contract violation
expected: pair?
given: '()
pointing to the (g (car s-inf)) call in append-map-inf.

Hopefully, by the time I finish the book, I'll be able to debug this myself, but I am not there yet.  Here is my code:

#lang racket
(require Racket-miniKanren/miniKanren/mk)
(define succeed (== #t #t))
(define fail (== #t #f))
(define else succeed)

; Frame 10:55 in Reasoned Schemer, 2nd ed
(define (append-inf s-inf t-inf)
(cond
((null? s-inf) t-inf)
((pair? s-inf)
(cons (car s-inf)
(append-inf (cdr s-inf) t-inf)))
(else (lambda()
(append-inf t-inf (s-inf))))))

; Frame 10:84 in Reasoned Schemer, 2nd ed
(define (append-map-inf g s-inf)
(cond
((null? s-inf) '())
((pair? s-inf)
(append-inf (g (car s-inf))
(append-map-inf g (cdr s-inf))))
(else (lambda ()
(append-map-inf g (s-inf))))))

; Frame 10:81 in Reasoned Schemer, 2nd ed
(define (conj2 g1 g2)
(lambda (s)
(append-map-inf g2 (g1 s))))

; Frame 1:50 in Reasoned Schemer, 2nd ed
(run* (q)
(conj2 succeed succeed)) ; runtime error

; Frame 1:51
(run* (q)
(conj2 succeed (== 'corn q))) ; runtime error

; Frame 1:52
(run* (q)
(conj2 fail (== 'corn q))) ; runtime error

[William Byrd]

Hi Jeff!

We just posted code for The Reasoned Schemer, Second Edition:

https://github.com/TheReasonedSchemer2ndEd/CodeFromTheReasonedSchemer2ndEd

Does this help?

Thanks!

--Will

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[Jeff Ward]

Yes, works like a charm.  Thanks!

[William Byrd]

w00t! :)

On Thu, Jun 14, 2018 at 4:59 PM, 'Jeff Ward' via minikanren
<minik...@googlegroups.com> wrote:
> Yes, works like a charm. Thanks!
>

[Jeff Ward]

Now I am having trouble in Chapter 3.  

> (run* x (listo '(a b c . ,x)))

'(_0)    ; According to Section 3:12, this should have no value

> (run 1 x (listo '(a b c . ,x)))

'(_0)    ; Also looks wrong to me

> (run 1 x (listo '(a b c . d)))

'()        ; But this seems correct

In order to get the above to evaluate, I added the following to trs2-impl.scm:

#lang racket ; at the beginning

...

; ... then these lines from The Reasoned Schemer 2nd ed to the end of the file:

; 2:5

(defrel (caro p a)

  (fresh (d)

         (== (cons a d) p)))

; 2:13

(defrel (cdro p d)

  (fresh (a)

         (== (cons a d) p)))

; 2:33

(defrel (nullo x)

  (== '() x))

; 3:8

(defrel (listo l)

  (conde

   ((nullo l))

   ((fresh (d)

           (cdro l d)

           (listo d)))))

Thanks for any help that you can give!

[Dakota Fisher]

In your queries, are those quotes supposed to be quotes (') or are they supposed to be quasiquotes (`)?

[Jason Hemann]

Hi,

It could be a fonting issue on my end but to double check, are those backticks? I think you want a quasiquote there, not a quote.

Hope that's it.

JBH

[Jeff Ward]

Thanks, Dakota and Jason!  That was the problem.