Re: and-let* is not composable?

[Stefan Israelsson Tampe]

First of all define-macro is asking for trouble. don't use it is the
general recomendation for guile.

If you look into the kanren soures you will find,

(define-syntax lambda@
  (syntax-rules ()
    ((_ (formal) body0 body1 ...) (lambda (formal) body0 body1 ...))
    ((_ (formal0 formal1 formal2 ...) body0 body1 ...)
     (lambda (formal0)
       (lambda@ (formal1 formal2 ...) body0 body1 ...)))))

(define-syntax @  
  (syntax-rules ()
    ((_ rator rand) (rator rand))
    ((_ rator rand0 rand1 rand2 ...) (@ (rator rand0) rand1 rand2 
...))))

That is currying where lambda@ is your define-curried and @ is the
application of curried functions in a convinient way e.g.

(test-check 'address@hidden@
  (@ (lambda@ (x y z) (+ x (+ y z))) 1 2 3)
  6)

It's not what you wnt but this gives you a good pattern to maybe base
your work on. If you still wan't to design defined curried ontop of 
syntax-rules I would recoment to use the ck macro e.g.

(define-syntax ck
  (syntax-rules (quote)
    ((ck () 'v) v)                      ; yield the value on empty stack

    ((ck (((op ...) ea ...) . s) 'v)    ; re-focus on the other 
argument, ea
     (ck-arg s (op ... 'v) ea ...))

    ((ck s (op ea ...))                 ; Focus: handling an 
application;
     (ck-arg s (op) ea ...))))          ; check if args are values

(define-syntax ck-arg
  (syntax-rules (quote)
    ((ck-arg s (op va ...))             ; all arguments are evaluated,
     (op s va ...))                     ; do the redex

    ((ck-arg s (op ...) 'v ea1 ...)     ; optimization when the first ea
     (ck-arg s (op ... 'v) ea1 ...))    ; was already a value

    ((ck-arg s (op ...) ea ea1 ...)     ; focus on ea, to evaluate it
     (ck (((op ...) ea1 ...) . s) ea))))


1) define a partitioner, (a b c) -> (() a) ((a) b) ((a b) c)) with
(define-syntax ck-partition 
  (syntax-rules (quote)
    ((_ s '(a ... b) 'l)    
     (ck-partition s '(a ...) '(((a ...) b) . l)))
    ((_ s '() 'l)
     (ck s 'l))))

2) compile the pieces together
(define-syntax compile-curried
  (syntax-rules (quote)
    ((_ s 'name '(a ...) 'body '(((b ...) c) ...))
      (ck ()
      '(define-syntax name
         (syntax-rules ()
           ((_ a ...) (begin . body))
           ((_ b ...) (lambda (c) (name b ... c)))
           ...))))))

3) The overall macro
(define-syntax-rule (define-curried (name a ...) . body)
  (ck () (compile-curried 'name '(a ...) 'body 
  (ck-partition '(a ...) '()))))

Now we need the definition of the ck macro,
  
  http://okmij.org/ftp/Scheme/macros.html

We have it in guile also in master. So lets try it, ...

scheme@(guile-user)>  (define-curried (f a b c d) (list a b c d))
scheme@(guile-user)> (((f 1 2) 3) 4)
$5 = (1 2 3 4)

it works, lets try out the problematic vode you have,

(use-modules (srfi srfi-2))
(use-modules (srfi srfi-1))

(define-curried (string-matches pattern string)
   (and-let* ((match-struct (string-match pattern string))
                 (count (match:count match-struct)))
      (map (lambda(n)(match:substring match-struct n))
         (iota (1- count) 1))))

scheme@(guile-user)> (string-matches "([a-z])" "a")
$4 = ("a")


,exp ((string-matches "([a-z])") "a")
$5 = ((lambda (string-871)
   (let ((match-struct-876
           (string-match "([a-z])" string)))
     (if match-struct-876
       (let ((count-880 (match:count match-struct-876)))
         (if count-880
           (map (lambda (n-883)
                  (match:substring match-struct-876 n-883))
                (iota (#{1-}# count-880) 1))
           #f))
       #f)))
 "a")

And we see that string is not managed correctly. Is this a bug? I
can't understand why this is not treated as intended!



> On Monday, September 09, 2013 07:35:16 PM Panicz Maciej Godek wrote:
> Hi,
> some time ago I posted to comp.lang.scheme with the
> following proposal of "define-curried" macro:
> 
> (define-macro (define-curried signature . body)
>   (match signature
>     ((name args ...)
>      `(define-syntax ,name
>         (syntax-rules ()
>           ((_ ,@args)
>            (begin ,@body))
>           ,@(let loop ((args* args))
>               (match args*
>                 (() '())
>                 ((first ... last)
>                  (cons `((_ ,@first #;...)
>                          (lambda(,last)(,name ,@args*)))
>                        (loop first #;...))))))))))
> 
> The idea was to expand, e.g. (define-curried (f a b c d) (list a b c
> d)) to:
> 
> (define-syntax f
>   (syntax-rules ()
>     ((_ a b c d)
>      (begin (list a b c d)))
>     ((_ a b c)
>      (lambda(d)
>        (f a b c d)))
>     ((_ a b)
>      (lambda(c)
>        (f a b c)))
>     ((_ a)
>      (lambda(b)
>        (f a b)))
>     ((_)
>      (lambda(a)
>        (f a)))))
> 
> I asked whether it would be possible to write that code using
> syntax-rules only, but I received no answer, not even a reprimend. I
> used that code to implement a quite convinient macro (actually that
> urge was my inspiration):
> 
> (define-curried (matches? pattern x)
>   (match x
>     (pattern #t)
>     (else #f)))
> 
> so that I could write
> 
> (filter (matches? (two elements)) some-list)
> 
> Recently, I tried to write a nicer interface to string-match, that
> would allow me to extract parenthesized subexpressions easily. My
> first guess was this:
> 
> (define-curried (string-matches pattern string)
>   ;;CAUTION: buggy version
>   (and-let* ((match-struct (string-match pattern string))
>                 (count (match:count match-struct)))
>      (map (lambda(n)(match:substring match-struct n))
>         (iota (1- count) 1))))
> 
> and although it worked with a complete list of arguments,
> (string-matches "([a-z])" "a")
> ==> ("a")
> it failed to curry properly
> ((string-matches "([a-z])") "a")
> ==> some strange error
> 
> It turned out, that the "string" symbol doesn't get tied
> with the lambda argument:
> 
> (expand (string-matches "([a-z])"))
> ==>
> (lambda (string-12552)
>   (let ((match-struct-12557 (string-match "([a-z])" string)))
> ;; the reason of our tears and despair is right here^^^
>     (if match-struct-12557
>         (let ((count-12561 (match:count match-struct-12557)))
>           (if count-12561
>               (map (lambda (n-12564)
>                      (match:substring match-struct-12557 n-12564))
>                    (iota (#{1-}# count-12561) 1))
>               #f))
>         #f)))
> 
> This forced me to write another definition of string-matches
> that doesn't use the and-let* macro and works as expected:
> 
> (define-curried (string-matches pattern s)
>   (let ((match-struct (string-match pattern s)))
>     (if match-struct
> (let ((count (match:count match-struct)))
>           (map (lambda(n)(match:substring match-struct n))
>                (iota (1- count) 1)))
>         #f)))
> 
> Nevertheless I am a little worried that either my macro,
> or and-let* is not composable. Perhaps there's some wise
> man here who knows what's going on.
> 
> Best regards,
> M.