Arc Forum | Oh nice. So is there a way using this trick to do a."b".c.d.g without parens?

Arc Forum

1 point by akkartik 4886 days ago | link | parent

Oh nice. So is there a way using this trick to do

  a."b".c.d.g

without parens?

3 points by rocketnia 4886 days ago | link

Not in Arc. The best you get is (.g:.d:.c:a "b"), I think. You can shove "b" into ssyntax with string!b, but you need to use it as an argument somehow, and any ssyntax containing .string!b will pass the 'string function itself as an argument instead of calling it first.

Of course, if "b" were a symbol instead of a string, it would just be "a!b.c.d.g".

In Penknife, the answer to your question is actually yes: It's "q.b'a.c.d.g", where q is the string-quoting operator and ' is an operator that acts like a reverse a.b. It's easy to stump Penknife too, but I'm hoping to make a full thread about Penknife's take on infix operators in a couple of days or so.

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2 points by thaddeus 4883 days ago | link

Optionally, in ac.scm:

  (define (has-ssyntax-char? string i)
    (and (>= i 0)
         (or (let ((c (string-ref string i)))
               (or (eqv? c #\:) (eqv? c #\~) 
                   (eqv? c #\&)                
                   (eqv? c #\%)                
                   ;(eqv? c #\_) 
                   (eqv? c #\.)(eqv? c #\!)))
             (has-ssyntax-char? string (- i 1)))))

  (define (expand-ssyntax sym)
    ((cond ((or (insym? #\: sym) (insym? #\~ sym)) expand-compose)
           ((or (insym? #\. sym) (insym? #\! sym)(insym? #\% sym)) expand-sexpr)
           ((insym? #\& sym) expand-and)
       ;   ((insym? #\_ sym) expand-curry)
           (#t (error "Unknown ssyntax" sym)))
   sym))

  (define (build-sexpr toks orig)
    (cond ((null? toks)
           'get)	    
          ((null? (cdr toks))
           (chars->value (car toks)))
          (#t
           (list (build-sexpr (cddr toks) orig)
                 (cond ((eqv? (cadr toks) #\!)
                        (list 'quote (chars->value (car toks))))
                       ((eqv? (cadr toks) #\%)
                         (list 'string (list 'quote (chars->value (car toks)))))
                       ((or (eqv? (car toks) #\.)(eqv? (car toks) #\!)(eqv? (car toks) #\$)(eqv? (car toks) #\%))
                         (err "Bad ssyntax" orig))
                       (#t 
                       (chars->value (car toks))))))))

Then:

  arc> (= test (obj "a" "my a val" "b" "my b val"))
  #hash(("a" . "my a val") ("b" . "my b val"))

  arc> test%a
  "my a val"

[edit: actually, it would be nicer to have the percent symbol represent the spaces in the string and have some other symbol signify string handling, but I never got around to it + my scheme foo is lacking :)]

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