multiple-value version of in-value

[Jos Koot]

 

Recently I needed a multiple value version of in-value.

Does something like that exist already?

I could not find it, so I made one:

 

(define-syntax (in-values stx)

(syntax-case stx ()

  ((_ expr)

#'(make-do-sequence

    (λ ()

     (values

      (λ (p) expr)

      (λ (p) #f)

      #t

      (λ (p) p)

      #f

      #f))))))

 

A pity that it is a syntax. It is possible to code it as a procedure, but I do not see an elegant way to do that without confusing a list with a multiple value.

 

I had:

 

File drac-plus-sant-is-jordi.rkt

 

(define digits '(0 1 2 3 4 5 6 7 8 9))

 

  (for*/list

   ((A (in-list digits)) (digits (in-value (remove A digits)))

    (C (in-list digits)) (digits (in-value (remove C digits)))

    (D (in-list digits)) (digits (in-value (remove D digits)))

    (N (in-list digits)) (digits (in-value (remove N digits)))

    (R (in-list digits)) (digits (in-value (remove R digits)))

    (S (in-list digits)) (digits (in-value (remove S digits)))

    (T (in-list digits))

    (DRAC  (in-value (+ (* 1000 D) (* 100 R) (* 10 A) C)))

    (SANT  (in-value (+ (* 1000 S) (* 100 A) (* 10 N) T)))

    (JØRDI (in-value (+ DRAC SANT))) ...

 

With syntax in-values I could simplify it to:

 

File drac-plus-sant-is-jordi-with-combi.rkt

 

  (for*/list

   ((combination (in-combinations '(0 1 2 3 4 5 6 7 8 9) 7))

    (permutation (in-permutations combination))

    ((A C D N R S T) (in-values (apply values permutation)))

    (DRAC  (in-value (+ (* 1000 D) (* 100 R) (* 10 A) C)))

    (SANT  (in-value (+ (* 1000 S) (* 100 A) (* 10 N) T)))

    (JØRDI (in-value (+ DRAC SANT)))

    (J (in-value (find-decimal-digit JØRDI 4)))

    (Ø (in-value (find-decimal-digit JØRDI 3)))

    (I (in-value (find-decimal-digit JØRDI 0))) ...

 

See https://github.com/joskoot/drac-sant-jordi for the complete programs.

 

Best wishes, Jos

[Philip McGrath]

My package `adjutor` has a few variants of this, like `in-value*`: https://docs.racket-lang.org/adjutor/Stable.html#(part._.Sequence_.Constructors)

They can all be used as first-class procedures, but that does involve a little runtime overhead, so they use `define-sequence-syntax` to cooperate directly with `for`-like forms when possible.

-Philip

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[Jos Koot]

Very nice. I have installed the package. Thanks very much,

Jos

[Jos Koot]

To Philip McGrath, Hi again

 

I modified the clause

((id ...) (in-value* expr ...))

to the following in-values clause:

((id ...) (in-values expr))

 

where the expr is supposed to return as many values as ids.

I simplified the code such as to avoid syntax-parse,

because I do not (yet) understand all its powerful features.

I prefer writing code I can understand in all details.

😉 I should study on syntax-parse in due future 😉

 

(define-sequence-syntax in-values

(λ (stx)

  (raise-syntax-error 'in-values

   "can only be used in for forms" stx))

(λ (stx)

  (syntax-case stx ()

   (((id ...) (_ expr))

  #'((id ...)

     (:do-in

      (((id ...) expr))

      #t () #t () #t #f ()))))))

 

For example:

 

(for/first (((a b c) (in-values (values 2 + 3)))) (b a c)) ; -> 5

 

Thanks again, Jos

 

From: Philip McGrath
Sent: 04 May 2020 17:21
To: Jos Koot
Cc: us...@racket-lang.org
Subject: Re: [racket-users] multiple-value version of in-value

 

My package `adjutor` has a few variants of this, like `in-value*`: https://docs.racket-lang.org/adjutor/Stable.html#(part._.Sequence_.Constructors)

[Philip McGrath]

Glad it was useful!

There is a variant `in-value*/expression` that works like your `in-values`: https://docs.racket-lang.org/adjutor/Stable.html#(form._((lib._adjutor%2Fmain..rkt)._in-value*%2Fexpression))

-Philip