;;;; loop.scm - the chibi loop (aka foof-loop)
;;
;; Copyright (c) 2009-2015 Alex Shinn.  All rights reserved.
;; BSD-style license: http://synthcode.com/license.txt

;;> The loop API is mostly compatible with Taylor Campbell's
;;> \hyperlink["http://mumble.net/~campbell/scheme/foof-loop.txt"]{foof-loop},
;;> but the iterator API is different and subject to change.

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(define (assoc-pred equal elt ls)
  (and (pair? ls)
       (if (equal elt (car (car ls)))
           (car ls)
           (assoc-pred equal elt (cdr ls)))))

(define-syntax let-keyword-form
  (syntax-rules ()
    ((let-keyword-form
      ((labeled-arg-macro-name (positional-name . params)))
      . body)
     (let-syntax
         ((labeled-arg-macro-name
           (er-macro-transformer
            (lambda (expr rename compare)
              (let lp ((ls (cdr expr)) (named '()) (posns '()))
                (cond
                 ((pair? ls)
                  (if (and (list? (car ls)) (compare (caar ls) (rename '=>)))
                      (lp (cdr ls) (cons (cdar ls) named) posns)
                      (lp (cdr ls) named (cons (car ls) posns))))
                 (else
                  (let lp ((ls (syntax-quote params))
                           (posns (reverse posns))
                           (args '()))
                    (cond
                     ((null? ls)
                      (if (pair? posns)
                          (error "let-keyword-form: too many args" expr)
                          (cons (syntax-quote positional-name) (reverse args))))
                     ((assoc-pred compare (caar ls) named)
                      => (lambda (x) (lp (cdr ls) posns (cons (cadr x) args))))
                     ((pair? posns)
                      (lp (cdr ls) (cdr posns) (cons (car posns) args)))
                     (else
                      (lp (cdr ls) posns (cons (car (cdar ls)) args))))))))))))
       . body))))

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;;> \macro{(loop [name] (vars ...) [=> result] body ...)}

(define-syntax loop
  (syntax-rules ()
    ;; unnamed, implicit recursion
    ((loop (vars ...) body ...)
     (%loop tmp-loop () () () () () (vars ...) body ... (tmp-loop)))
    ;; named, explicit recursion
    ((loop name (vars ...) body ...)
     (%loop name () () () () () (vars ...) body ...))))

;; Main LOOP macro. Separate the variables from the iterator and
;; parameters, then walk through each parameter expanding the
;; bindings, and build the final form.

(define-syntax %loop
  (syntax-rules (=> for with let while until)
    ;; automatic iteration
    ((_ name l v c r f ((for var1 (iterator source ...)) rest ...) . body)
     (iterator ((var1) (source ...)) %loop-next name l v c r f (rest ...) . body))
    ((_ name l v c r f ((for var1 var2 (iterator source ...)) rest ...) . body)
     (iterator ((var1 var2) (source ...)) %loop-next name l v c r f (rest ...) . body))
    ((_ name l v c r f ((for var1 var2 var3 (iterator source ...)) rest ...) . body)
     (iterator ((var1 var2 var3) (source ...)) %loop-next name l v c r f (rest ...) . body))
    ((_ name l v c r f ((for var1 var2 var3 var4 (iterator source ...)) rest ...) . body)
     (iterator ((var1 var2 var3 var4) (source ...)) %loop-next name l v c r f (rest ...) . body))
    ;; do equivalents, with optional guards
    ((_ name l (vars ...) (checks ...) r f ((with var init step guard) rest ...) . body)
     (%loop name l (vars ... (var init step)) (checks ... (guard var)) r f (rest ...) . body))
    ((_ name l (vars ...) c r f ((with var init step) rest ...) . body)
     (%loop name l (vars ... (var init step)) c r f (rest ...) . body))
    ((_ name l (vars ...) c r f ((with var init) rest ...) . body)
     (%loop name l (vars ... (var init var)) c r f (rest ...) . body))
    ;; user-specified terminators
    ((_ name l vars (checks ...) r f ((until expr) rest ...) . body)
     (%loop name l vars (checks ... expr) r f (rest ...) . body))
    ((_ name l vars (checks ...) r f ((while expr) rest ...) . body)
     (%loop name l vars (checks ... (not expr)) r f (rest ...) . body))
    ;; specify a default done?
    ((_ name l v c r f ())
     (%loop name l v c r f () (#f #f)))
    ((_ name l v c r f () () . body)
     (%loop name l v c r f () (#f #f) . body))
    ;; final expansion
    ((_ name (lets ...) ((var init step) ...) (checks ...) (refs ...) (finals ...) ()
        => result
        . body)
     (let* (lets ...)
       (letrec ((tmp (lambda (var ...)
                       (if (or checks ...)
                           (let-keyword-form ((name (tmp (var step) ...)))
                             (let (finals ...) result))
                           (let (refs ...)
                             (let-keyword-form ((name (tmp (var step) ...)))
                               (if #f #f)
                               . body))))))
         (tmp init ...))))
    ;; unspecified return value case
    ((_ name (lets ...) ((var init step) ...) (checks ...) (refs ...) (finals ...) ()
        . body)
     (%loop name (lets ...) ((var init step) ...) (checks ...) (refs ...) (finals ...) ()
            => (if #f #f) . body))
    ))

(define-syntax %loop-next
  (syntax-rules ()
    ((_ (new-lets ...) (new-vars ...) (new-checks ...) (new-refs ...) (new-finals ...)
        name (lets ...) (vars ...) (checks ...) (refs ...) (finals ...)
        . rest)
     (%loop name (lets ... new-lets ...) (vars ... new-vars ...)
                 (checks ... new-checks ...) (refs ... new-refs ...)
                 (finals ... new-finals ...)
        . rest))))

;;> Utility syntax for the common case of a loop which has only
;;> \scheme{for} clauses.

(define-syntax for
  (syntax-rules ()
    ((for ((vars ...) ...) body ...)
     (loop ((for vars ...) ...) body ...))
    ((for lp ((vars ...) ...) body ...)
     (loop lp ((for vars ...) ...) body ...))))

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;;> \section{Iterators}

;; Each gets passed two lists, those items left of the macro and those to
;; the right, followed by a NEXT and REST continuation.
;;
;; Should finish with
;;
;; \schemeblock{
;;  (next (outer-vars ...) (cursor-vars ...) (done?-tests ...)
;;        (loop-vars ...) (final-vars ...) . rest)
;; }
;;
;; \itemlist[
;; \item{\var{outer-vars} - bound once outside the loop in a LET*}
;; \item{\var{cursor-vars} - DO-style bindings of the form (name init update)}
;; \item{\var{done?-tests} - possibly empty list of forms that terminate the loop on #t}
;; \item{\var{loop-vars} - inner variables, updated in parallel after the cursors}
;; \item{\var{final-vars} - final variables, bound only in the => result}
;; ]

;;> \macro{(for var [pair] (in-list ls [cdr]))}

;;> Basic list iterator.

(define-syntax in-list                  ; called just "IN" in ITER
  (syntax-rules ()
    ((in-list ((var) source) next . rest)
     (in-list ((var cursor) source) next . rest))
    ((in-list ((var cursor) source) next . rest)
     (in-list ((var cursor succ) source) next . rest))
    ((in-list ((var cursor succ) (source)) next . rest)
     (next ()                         ; outer let bindings
           ((cursor source succ))     ; iterator, init, step
           ((not (pair? cursor)))     ; finish tests for iterator vars
           ;; step variables and values
           ((var (car cursor))
            (succ (cdr cursor)))
           ()                           ; final result bindings
           . rest))
    ((in-list ((var cursor succ) (source step)) next . rest)
     (next ()
           ((cursor source succ))
           ((not (pair? cursor)))
           ((var (car cursor))
            (succ (step cursor)))
           ()
           . rest))))

;;> \macro{(for elts [pairs] (in-lists lol [cdr [done?]]))}

;;> Iterator from Taylor R. Campbell.  If you know the number of lists
;;> ahead of time it's much more efficient to iterate over each one
;;> separately.

(define-syntax in-lists
  (syntax-rules ()
    ((in-lists ((elts) lol) next . rest)
     (in-lists ((elts pairs) lol) next . rest))
    ((in-lists ((elts pairs) lol) next . rest)
     (in-lists ((elts pairs succ) lol) next . rest))
    ((in-lists ((elts pairs succ) (lol)) next . rest)
     (in-lists ((elts pairs succ) (lol cdr)) next . rest))
    ((in-lists ((elts pairs succ) (lol)) next . rest)
     (in-lists ((elts pairs succ) (lol cdr)) next . rest))
    ((in-lists ((elts pairs succ) (lol step)) next . rest)
     (in-lists ((elts pairs succ) (lol step null?)) next . rest))
    ((in-lists ((elts pairs succ) (lol step done?)) next . rest)
     (next ()
           ((pairs lol succ))
           ((let lp ((ls pairs)) ; an in-lined ANY
              (and (pair? ls) (if (done? (car ls)) #t (lp (cdr ls))))))
           ((elts (map car pairs))
            (succ (map step pairs)))
           ()
           . rest))
    ))

(define-syntax define-in-indexed
  (syntax-rules ()
    ((define-in-indexed in-type in-type-reverse length ref)
     (begin
       (define-syntax in-type
         (syntax-rules ()
           ((in-type seq next . rest)
            (%in-idx >= (lambda (x i) (+ i 1)) (lambda (x) 0) length ref tmp seq next . rest))))
       (define-syntax in-type-reverse
         (syntax-rules ()
           ((in-type-reverse seq next . rest)
            (%in-idx < (lambda (x i) (- i 1)) (lambda (x) (- (length x) 1)) (lambda (x) 0) ref tmp seq next . rest))))
       ))))

(define-in-indexed in-vector in-vector-reverse vector-length vector-ref)

;;> \macro{(for var [index] (in-vector vec))}
;;> \macro{(for var [index] (in-vector-reverse vec))}

;;> \macro{(for ch [cursor] (in-string str))}

(define-syntax in-string
  (syntax-rules ()
    ((in-string s next . rest)
     (%in-idx string-cursor>=? string-cursor-next
              string-cursor-start string-cursor-end string-cursor-ref
              tmp s next . rest))))

;;> \macro{(for ch [cursor] (in-string-reverse str))}

(define-syntax in-string-reverse
  (syntax-rules ()
    ((in-string-reverse s next . rest)
     (%in-idx string-cursor<? string-cursor-prev
              (lambda (x) (string-cursor-prev x (string-cursor-end x)))
              string-cursor-start string-cursor-ref
              tmp s next . rest))))

;; helper for the above string and vector iterators
(define-syntax %in-idx
  (syntax-rules ()
    ;;   cmp inc start end ref
    ((%in-idx ge + s e r tmp ((var) (seq ...)) next . rest)
     (%in-idx ge + s e r tmp ((var seq-index) (seq ...)) next . rest))
    ((%in-idx ge + s e r tmp ((var index) (seq)) next . rest)
     (%in-idx ge + s e r tmp ((var index) (seq (s tmp) (e tmp))) next . rest))
    ((%in-idx ge + s e r tmp ((var index) (seq from)) next . rest)
     (%in-idx ge + s e r tmp ((var index) (seq from (e tmp))) next . rest))
    ((%in-idx ge + s e r tmp ((var index) (seq from to)) next . rest)
     (next ((tmp seq) (end to))
           ((index from (+ tmp index)))
           ((ge index end))
           ((var (r tmp index)))
           ()
       . rest))
    ))

;;> \macro{(for ch (in-port [input-port [reader [eof?]]]))}

(define-syntax in-port
  (syntax-rules ()
    ((in-port ((var) source) next . rest)
     (in-port ((var p) source) next . rest))
    ((in-port ((var p) ()) next . rest)
     (in-port ((var p) ((current-input-port))) next . rest))
    ((in-port ((var p) (port)) next . rest)
     (in-port ((var p) (port read-char)) next . rest))
    ((in-port ((var p) (port read-char)) next . rest)
     (in-port ((var p) (port read-char eof-object?)) next . rest))
    ((in-port ((var p) (port reader eof?)) next . rest)
     (next ((p port) (r reader) (e? eof?))
           ((var (r p) (r p)))
           ((e? var))
           ()
           ()
       . rest))))

;;> \macro{(for ch (in-file [input-port [reader [eof?]]]))}

(define-syntax in-file
  (syntax-rules ()
    ((in-file ((var) source) next . rest)
     (in-file ((var p) source) next . rest))
    ((in-file ((var p) (file)) next . rest)
     (in-file ((var p) (file read-char)) next . rest))
    ((in-file ((var p) (file reader)) next . rest)
     (in-file ((var p) (file reader eof-object?)) next . rest))
    ((in-file ((var p) (file reader eof?)) next . rest)
     (next ((p (open-input-file file)) (r reader) (e? eof?))
           ((var (r p) (r p)))
           ((e? var))
           ()
           ((dummy (close-input-port p)))
       . rest))))

;;> \macro{(for x (up-from [start] [(to limit)] [(by step)]))}

(define-syntax up-from
  (syntax-rules (to by)
    ((up-from (() . args) next . rest)
     (up-from ((var) . args) next . rest))
    ((up-from ((var) (start (to limit) (by step))) next . rest)
     (next ((s start) (l limit) (e step))
           ((var s (+ var e)))
           ((>= var l))
           ()
           ()
           . rest))
    ((up-from ((var) (start (to limit))) next . rest)
     (next ((s start) (l limit))
           ((var s (+ var 1)))
           ((>= var l))
           ()
           ()
           . rest))
    ((up-from ((var) (start (by step))) next . rest)
     (next ((s start) (e step)) ((var s (+ var e))) () () () . rest))
    ((up-from ((var) (start)) next . rest)
     (next ((s start)) ((var s (+ var 1))) () () () . rest))
    ))

;;> \macro{(for x (down-from [start] [(to limit)] [(by step)]))}

(define-syntax down-from
  (syntax-rules (to by)
    ((down-from (() . args) next . rest)
     (down-from ((var) . args) next . rest))
    ((down-from ((var) (start (to limit) (by step))) next . rest)
     (next ((s start) (l limit) (e step))
           ((var (- s e) (- var e)))
           ((< var l))
           ()
           ()
           . rest))
    ((down-from ((var) (start (to limit))) next . rest)
     (next ((s start) (l limit))
           ((var (- s 1) (- var 1)))
           ((< var l))
           ()
           ()
           . rest))
    ((down-from ((var) (start (by step))) next . rest)
     (next ((s start) (e step)) ((var (- s e) (- var e))) () () ()
           . rest))
    ((down-from ((var) (start)) next . rest)
     (next ((s start)) ((var (- s 1) (- var 1))) () () ()
           . rest))
    ))

(define-syntax accumulating
  (syntax-rules (initial if)
    ((accumulating (kons final init) ((var) . x) next . rest)
     (accumulating (kons final init) ((var cursor) . x) next . rest))
    ((accumulating (kons final init) ((var cursor) ((initial i) . x)) n . rest)
     (accumulating (kons final i) ((var cursor) x) n . rest))
    ((accumulating (kons final init) ((var cursor) (expr (if check))) n . rest)
     (n ((tmp-kons kons))
        ((cursor '() (if check (tmp-kons expr cursor) cursor)))
        ()
        ()
        ((var (final cursor)))
        . rest))
    ((accumulating (kons final init) ((var cursor) (expr)) n . rest)
     (n ((tmp-kons kons))
        ((cursor '() (tmp-kons expr cursor)))
        ()
        ()
        ((var (final cursor)))
        . rest))))

;;> \macro{(for x [pair] (listing expr))}

(define-syntax listing
  (syntax-rules ()
    ((listing args next . rest)
     (accumulating (cons reverse '()) args next . rest))))

;;> \macro{(for x [pair] (listing-reverse expr))}

(define-syntax listing-reverse
  (syntax-rules ()
    ((listing-reverse args next . rest)
     (accumulating (cons (lambda (x) x) '()) args next . rest))))

(define (append-reverse rev tail)
  (if (null? rev) tail (append-reverse (cdr rev) (cons (car rev) tail))))

;;> \macro{(for x [pair] (appending expr))}

(define-syntax appending
  (syntax-rules ()
    ((appending args next . rest)
     (accumulating (append-reverse reverse '()) args next . rest))))

;;> \macro{(for x [pair] (appending-reverse expr))}

(define-syntax appending-reverse
  (syntax-rules ()
    ((appending-reverse args next . rest)
     (accumulating (append-reverse (lambda (x) x) '()) args next . rest))))

;;> \macro{(for x (summing expr))}

(define-syntax summing
  (syntax-rules ()
    ((summing args next . rest)
     (accumulating (+ (lambda (x) x) 0) args next . rest))))

;;> \macro{(for x (multiplying expr))}

(define-syntax multiplying
  (syntax-rules ()
    ((multiplying args next . rest)
     (accumulating (* (lambda (x) x) 1) args next . rest))))
