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;;;; pprint.scm --- pretty-printing objects for CGEN
;;;; Copyright (C) 2005, 2009 Red Hat, Inc.
;;;; This file is part of CGEN.
;;;; See file COPYING.CGEN for details.
;;; This file defines a printing function PPRINT, and some hooks to
;;; let you print certain kind of objects in a summary way, and get at
;;; their full values later.
;;; PPRINT is a printer for Scheme objects that prints lists or
;;; vectors that contain shared structure or cycles and prints them in
;;; a finite, legible way.
;;;
;;; Ordinary values print in the usual way:
;;;
;;;   guile> (pprint '(1 #(2 3) 4))
;;;   (1 #(2 3) 4)
;;;
;;; Values can share structure:
;;; 
;;;   guile> (let* ((c (list 1 2))
;;;                 (d (list c c)))
;;;            (write d)
;;;            (newline))
;;;   ((1 2) (1 2))
;;;
;;; In that list, the two instances of (1 2) are actually the same object;
;;; the top-level list refers to the same object twice.
;;;
;;; Printing that structure with PPRINT shows the sharing:
;;; 
;;;   guile> (let* ((c (list 1 2))
;;;                 (d (list c c)))
;;;            (pprint d))
;;;   (#0=(1 2) #0#)
;;;
;;; Here the "#0=" before the list (1 2) labels it with the number
;;; zero.  Then, the "#0#" as the second element of the top-level list
;;; indicates that the object appears here, too, referring to it by
;;; its label.
;;;
;;; If you have several objects that appear more than once, they each
;;; get a separate label:
;;;
;;;   guile> (let* ((a (list 1 2))
;;;                 (b (list 3 4))
;;;                 (c (list a b a b)))
;;;            (pprint c))
;;;   (#0=(1 2) #1=(3 4) #0# #1#)
;;;
;;; Cyclic values just share structure with themselves:
;;;
;;;   guile> (let* ((a (list 1 #f)))
;;;            (set-cdr! a a)
;;;            (pprint a))
;;;   #0=(1 . #0#)
;;;
;;;
;;; PPRINT also consults the function ELIDE? and ELIDED-NAME to see
;;; whether it should print a value in a summary form.  You can
;;; re-define those functions to customize PPRINT's behavior;
;;; cos-pprint.scm defines them to handle COS objects and classes
;;; nicely.
;;;
;;; (ELIDE? OBJ) should return true if OBJ should be elided.
;;; (ELIDED-NAME OBJ) should return a (non-cyclic!) object to be used
;;; as OBJ's abbreviated form.
;;;
;;; PPRINT prints an elided object as a list ($ N NAME), where NAME is
;;; the value returned by ELIDED-NAME to stand for the object, and N
;;; is a number; each elided object gets its own number.  You can refer
;;; to the elided object number N as ($ N).
;;;
;;; For example, if you've loaded CGEN, pprint.scm, and cos-pprint.scm
;;; (you must load cos-pprint.scm *after* loading pprint.scm), you can
;;; print a list containing the <insn> and <ident> classes:
;;;
;;;   guile> (pprint (list <insn> <ident>))
;;;   (($ 1 (class <insn>)) ($ 2 (class <ident>)))
;;;   guile> (class-name ($ 1))
;;;   <insn>
;;;   guile> (class-name ($ 2))
;;;   <ident>
;;;
;;; As a special case, PPRINT never elides the object that was passed
;;; to it directly.  So you can look inside an elided object by doing
;;; just that:
;;;
;;;   guile> (pprint ($ 2))
;;;   #0=#("class" <ident> () ((name #:unbound #f . 0) ...
;;;
;;; A list of elided objects, larger numbers first, and the number of
;;; the first element.
;;; Add OBJ to the elided object list, and return its number.
;;; Referencing elided objects.
"no such object";;; A default predicate for elision.
;;; If (elide? OBJ) is true, return some sort of abbreviated list
;;; structure that might be helpful to the user in identifying the
;;; elided object.
;;; A default definition.
"";;; This is a pretty-printer that handles cyclic and shared structure.
;; Return true if OBJ should be elided in this call to pprint.
;; (We never elide the object we were passed itself.)
;; First, traverse OBJ and build a hash table mapping objects
;; referenced more than once to #t, and everything else to #f.
;; (Only include entries for objects that might be interior nodes:
;; pairs and vectors.)
;; Guile's stupid hash tables don't resize the table; the
;; chains just get longer and longer.  So we need a big value here.
"unhandled interior type";; A counter for shared structure labels.
;; Print an object OBJ, which SHARED maps to L.
;; L is always (hashq-ref shared obj), but we have that value handy
;; at times, so this entry point lets us avoid looking it up again.
;; If we've already visited this object, just print a
;; reference to its label.
"#""#";; If it needs a label, attach one now.
"#""=";; Print the object.
"(""#("" "")";; Print a pair P as if it were the tail of a list; assume the
;; opening paren and any previous elements have been printed.
")";; We use the dotted pair syntax if the cdr isn't a pair, but
;; also if it needs to be labeled.
" . "")"" "