432 lines
12 KiB
Scheme
432 lines
12 KiB
Scheme
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; Copyright (c) 1993, 1994 Richard Kelsey and Jonathan Rees. See file COPYING.
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;;;; A pretty-printer
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; This isn't exactly in the spirit of the rest of the Scheme 48
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; system. It's too hairy, and it has unexploited internal generality.
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; It really ought to be rewritten. In addition, it seems to be buggy
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; -- it sometimes prints unnecessarily wide lines. Usually it's
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; better than no pretty printer at all, so we tolerate it.
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; From: ramsdell@linus.mitre.org
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; Date: Wed, 12 Sep 1990 05:14:49 PDT
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;
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; As you noted in your comments, pp.scm is not a straight forward
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; program. You could add some comments that would greatly ease the task
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; of figuring out what his going on. In particular, you should describe
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; the interface of various objects---most importantly the interface of a
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; formatter. You might also add some description as to what protocol
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; they are to follow.
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; Other things to implement some day:
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; - LET, LET*, LETREC binding lists should be printed vertically if longer
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; than about 30 characters
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; - COND clauses should all be printed vertically if the COND is vertical
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; - Add an option to lowercase or uppercase symbols and named characters.
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; - Parameters controlling behavior of printer should be passed around
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; - Do something about choosing between #f and ()
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; - Insert line breaks intelligently following head of symbol-headed list,
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; when necessary
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; - Some equivalents of *print-level*, *print-length*, *print-circle*.
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; Possible strategies:
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; (foo x y z) Horizontal = infinity sticky
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; (foo x y One sticky + one + body (e.g. named LET)
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; z
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; w)
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; (foo x One + body
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; y
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; z)
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; (foo x Two + body
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; y
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; z)
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; (foo x Big ell = infinity + body (combination)
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; y
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; z)
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; (foo Little ell, zero + body (combination)
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; x
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; y)
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; (foo Vertical
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; x
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; y)
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;
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; Available height/width tradeoffs:
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; Combination:
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; Horizontal, big ell, or little ell.
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; Special form:
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; Horizontal, or M sticky + N + body.
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; Random (e.g. vector, improper list, non-symbol-headed list):
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; Horizontal, or vertical. (Never zero plus body.)
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(define (p x . port-option)
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(let ((port (if (pair? port-option) (car port-option)
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(current-output-port))))
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(pretty-print x port 0)
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(newline port)))
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(define *line-width* 80)
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(define *single-line-special-form-limit* 30)
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; Stream primitives
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(define head car)
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(define (tail s) (force (cdr s)))
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(define (map-stream proc stream)
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(cons (proc (head stream))
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(delay (map-stream proc (tail stream)))))
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(define (stream-ref stream n)
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(if (= n 0)
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(head stream)
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(stream-ref (tail stream) (- n 1))))
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; Printer
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(define (pretty-print obj port pos)
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(let ((node (pp-prescan obj 0)))
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; (if (> (column-of (node-dimensions node)) *line-width*)
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; ;; Eventually add a pass to change format of selected combinations
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; ;; from big-ell to little-ell.
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; (begin (display ";** too wide - ")
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; (write (node-dimensions node))
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; (newline)))
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(print-node node port pos)))
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(define make-node list)
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(define (node-dimensions node)
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((car node)))
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(define (node-pass-2 node pos)
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((cadr node) pos))
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(define (print-node node port pos)
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((caddr node) port pos))
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(define (pp-prescan obj hang)
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(cond ((symbol? obj)
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(make-leaf (string-length (symbol->string obj))
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obj hang))
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((number? obj)
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(make-leaf (string-length (number->string obj))
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obj hang))
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((boolean? obj)
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(make-leaf 2 obj hang))
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((string? obj)
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;;++ Should count number of backslashes and quotes
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(make-leaf (+ (string-length obj) 2) obj hang))
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((char? obj)
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(make-leaf (case obj
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((#\space) 7)
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((#\newline) 9)
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(else 3))
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obj hang))
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((pair? obj)
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(pp-prescan-pair obj hang))
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((vector? obj)
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(pp-prescan-vector obj hang))
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(else
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(pp-prescan-random obj hang))))
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(define (make-leaf width obj hang)
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(let ((width (+ width hang)))
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(make-node (lambda () width)
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(lambda (pos)
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(+ pos width))
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(lambda (port pos)
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(write obj port)
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(do ((i 0 (+ i 1)))
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((>= i hang) (+ pos width))
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(write-char #\) port))))))
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(define (make-prefix-node string node)
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(let ((len (string-length string)))
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(make-node (lambda ()
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(+ (node-dimensions node) len))
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(lambda (pos)
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(node-pass-2 node (+ pos len)))
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(lambda (port pos)
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(display string port)
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(print-node node port (+ pos len))))))
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(define (pp-prescan-vector obj hang)
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(if (= (vector-length obj) 0)
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(make-leaf 3 obj hang)
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(make-prefix-node "#" (pp-prescan-list (vector->list obj) #t hang))))
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; Improve later.
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(define (pp-prescan-random obj hang)
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(let ((l (disclose obj)))
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(if (list? l)
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(make-prefix-node "#." (pp-prescan-list l #t hang))
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(make-leaf 25 obj hang)))) ;Very random number
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(define (pp-prescan-pair obj hang)
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(cond ((read-macro-inverse obj)
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=>
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(lambda (inverse)
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(make-prefix-node inverse (pp-prescan (cadr obj) hang))))
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(else
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(pp-prescan-list obj #f hang))))
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(define (pp-prescan-list obj random? hang)
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(let loop ((l obj) (z '()))
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(if (pair? (cdr l))
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(loop (cdr l)
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(cons (pp-prescan (car l) 0) z))
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(make-list-node
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(reverse
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(if (null? (cdr l))
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(cons (pp-prescan (car l) (+ hang 1)) z)
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(cons (make-prefix-node ". " (pp-prescan (cdr l) (+ hang 1)))
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(cons (pp-prescan (car l) 0) z))))
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obj
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(or random? (not (null? (cdr l))))))))
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; Is it sufficient to tell parent node:
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; At a cost of X line breaks, I can make myself narrower by Y columns. ?
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; Then how do we decide whether we narrow ourselves or some of our children?
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(define (make-list-node node-list obj random?)
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(let* ((random? (or random?
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;; Heuristic for things like do, cond, let, ...
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(not (symbol? (car obj)))
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(eq? (car obj) 'else)))
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(probe (if (not random?)
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(indentation-for (car obj))
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#f))
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(format horizontal-format)
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(dimensions (compute-dimensions node-list format))
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(go-non-horizontal
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(lambda (col)
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(set! format
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(cond (random? vertical-format)
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(probe (probe obj))
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(else big-ell-format)))
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(let* ((start-col (+ col 1))
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(col (node-pass-2 (car node-list) start-col))
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(final-col
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(format (cdr node-list)
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(lambda (node col target-col)
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(node-pass-2 node target-col))
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start-col
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(+ col 1)
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col)))
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(set! dimensions (compute-dimensions node-list format))
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final-col))))
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(if (> dimensions
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(if probe
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*single-line-special-form-limit*
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*line-width*))
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(go-non-horizontal 0))
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(make-node (lambda () dimensions)
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(lambda (col) ;Pass 2: if necessary, go non-horizontal
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(let ((defacto (+ col (column-of dimensions))))
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(if (> defacto *line-width*)
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(go-non-horizontal col)
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defacto)))
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(lambda (port pos)
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(write-char #\( port)
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(let* ((pos (+ pos 1))
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(start-col (column-of pos))
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(pos (print-node (car node-list) port pos)))
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(format (cdr node-list)
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(lambda (node pos target-col)
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(let ((pos (go-to-column target-col
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port pos)))
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(print-node node port pos)))
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start-col
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(+ (column-of pos) 1)
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pos))))))
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(define (compute-dimensions node-list format)
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(let* ((start-col 1) ;open paren
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(pos (+ (make-position start-col 0)
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(node-dimensions (car node-list)))))
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(format (cdr node-list)
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(lambda (node pos target-col)
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(let* ((dims (node-dimensions node))
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(lines (+ (line-of pos) (line-of dims)))
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(width (+ target-col (column-of dims))))
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(if (>= (column-of pos) target-col)
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;; Line break required
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(make-position
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(max (column-of pos) width)
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(+ lines 1))
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(make-position width lines))))
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start-col
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(+ (column-of pos) 1) ;first-col
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pos)))
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; Three positions are significant
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; (foo baz ...)
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; ^ ^ ^
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; | | +--- (column-of pos)
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; | +------ first-col
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; +---------- start-col
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; Separators
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(define on-same-line
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(lambda (start-col first-col pos)
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start-col first-col ;ignored
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(+ (column-of pos) 1)))
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(define indent-under-first
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(lambda (start-col first-col pos)
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start-col ;ignored
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first-col))
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(define indent-for-body
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(lambda (start-col first-col pos)
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first-col ;ignored
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(+ start-col 1)))
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(define indent-under-head
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(lambda (start-col first-col pos)
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first-col ;ignored
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start-col))
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; Format constructors
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(define (once separator format)
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(lambda (tail proc start-col first-col pos)
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(if (null? tail)
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pos
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(let ((target-col (separator start-col first-col pos)))
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(format (cdr tail)
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proc
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start-col
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first-col
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(proc (car tail) pos target-col))))))
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(define (indefinitely separator)
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(letrec ((self (once separator ;eta
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(lambda (tail proc start-col first-col pos)
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(self tail proc start-col first-col pos)))))
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self))
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(define (repeatedly separator count format)
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(do ((i 0 (+ i 1))
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(format format
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(once separator format)))
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((>= i count) format)))
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; Particular formats
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(define vertical-format
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(indefinitely indent-under-head))
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(define horizontal-format
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(indefinitely on-same-line))
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(define big-ell-format
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(indefinitely indent-under-first))
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(define little-ell-format
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(indefinitely indent-for-body))
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(define format-for-named-let
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(repeatedly on-same-line 2 (indefinitely indent-for-body)))
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(define hook-formats
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(letrec ((stream (cons little-ell-format
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(delay (map-stream (lambda (format)
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(once indent-under-first format))
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stream)))))
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stream))
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; Hooks for special forms.
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; A hook maps an expression to a format.
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(define (compute-let-indentation exp)
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(if (and (not (null? (cdr exp)))
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(symbol? (cadr exp)))
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format-for-named-let
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(stream-ref hook-formats 1)))
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(define hook
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(let ((hooks (map-stream (lambda (format)
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(lambda (exp) exp ;ignored
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format))
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hook-formats)))
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(lambda (n)
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(stream-ref hooks n))))
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; Table of indent hooks.
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(define indentations (make-table))
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(define (indentation-for name)
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(table-ref indentations name))
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(define (define-indentation name n)
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(table-set! indentations
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name
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(if (integer? n) (hook n) n)))
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; Indent hooks for Revised^n Scheme.
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(for-each (lambda (name)
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(define-indentation name 1))
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'(lambda define define-syntax let* letrec let-syntax letrec-syntax
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case call-with-values call-with-input-file
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call-with-output-file with-input-from-file
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with-output-to-file syntax-rules))
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(define-indentation 'do 2)
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(define-indentation 'call-with-current-continuation 0)
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(define-indentation 'let compute-let-indentation)
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; Kludge to force vertical printing (do AND and OR as well?)
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||
|
|
(define-indentation 'if (lambda (exp) big-ell-format))
|
||
|
|
(define-indentation 'cond (lambda (exp) big-ell-format))
|
||
|
|
|
||
|
|
|
||
|
|
; Other auxiliaries
|
||
|
|
|
||
|
|
(define (go-to-column target-col port pos) ;=> pos
|
||
|
|
;; Writes at least one space or newline
|
||
|
|
(let* ((column (column-of pos))
|
||
|
|
(line (if (>= column target-col)
|
||
|
|
(+ (line-of pos) 1)
|
||
|
|
(line-of pos))))
|
||
|
|
(do ((column (if (>= column target-col)
|
||
|
|
(begin (newline port) 0)
|
||
|
|
column)
|
||
|
|
(+ column 1)))
|
||
|
|
((>= column target-col)
|
||
|
|
(make-position column line))
|
||
|
|
(write-char #\space port))))
|
||
|
|
|
||
|
|
(define (make-position column line)
|
||
|
|
(+ column (* line 1000)))
|
||
|
|
|
||
|
|
(define (column-of pos)
|
||
|
|
(remainder pos 1000))
|
||
|
|
|
||
|
|
(define (line-of pos)
|
||
|
|
(quotient pos 1000))
|
||
|
|
|
||
|
|
(define (read-macro-inverse x)
|
||
|
|
(cond ((and (pair? x)
|
||
|
|
(pair? (cdr x))
|
||
|
|
(null? (cddr x)))
|
||
|
|
(case (car x)
|
||
|
|
((quote) "'")
|
||
|
|
((quasiquote) "`")
|
||
|
|
((unquote) ",")
|
||
|
|
((unquote-splicing) ",@")
|
||
|
|
(else #f)))
|
||
|
|
(else #f)))
|
||
|
|
|
||
|
|
; For the command processor:
|
||
|
|
|
||
|
|
;(define-command 'p "<exp>" "pretty-print" '(expression)
|
||
|
|
; (p (eval expression (user-package)) (command-output)))
|