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+;;; srfi-69.scm --- Basic hash tables
+
+;; 	Copyright (C) 2007 Free Software Foundation, Inc.
+;;
+;; This library is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU Lesser General Public
+;; License as published by the Free Software Foundation; either
+;; version 2.1 of the License, or (at your option) any later version.
+;; 
+;; This library is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;; Lesser General Public License for more details.
+;; 
+;; You should have received a copy of the GNU Lesser General Public
+;; License along with this library; if not, write to the Free Software
+;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+
+;;;; Commentary:
+
+;; My `hash' is compatible with core `hash', so I replace it.
+;; However, my `hash-table?' and `make-hash-table' are different, so
+;; importing this module will warn about them.  If you don't rename my
+;; imports, you shouldn't use both my hash tables and Guile's hash
+;; tables in the same module.
+;;
+;; SRFI-13 `string-hash' and `string-hash-ci' have more arguments, but
+;; are compatible with my `string-hash' and `string-ci-hash', and are
+;; furthermore primitive in Guile, so I use them as my own.
+;;
+;; I also have the extension of allowing hash functions that require a
+;; second argument to be used as the `hash-table-hash-function', and use
+;; these in defaults to avoid an indirection in the hashx functions.  The
+;; only deviation this causes is:
+;;
+;;  ((hash-table-hash-function (make-hash-table)) obj)
+;;  error> Wrong number of arguments to #<primitive-procedure hash>
+;;
+;; I don't think that SRFI 69 actually specifies that I *can't* do this,
+;; because it only implies the signature of a hash function by way of the
+;; named, exported hash functions.  However, if this matters enough I can
+;; add a private derivation of hash-function to the srfi-69:hash-table
+;; record type, like associator is to equivalence-function.
+;;
+;; Also, outside of the issue of how weak keys and values are referenced
+;; outside the table, I always interpret key equivalence to be that of
+;; the `hash-table-equivalence-function'.  For example, given the
+;; requirement that `alist->hash-table' give earlier associations
+;; priority, what should these answer?
+;;
+;;  (hash-table-keys
+;;   (alist->hash-table '(("xY" . 1) ("Xy" . 2)) string-ci=?))
+;;
+;;  (let ((ht (make-hash-table string-ci=?)))
+;;    (hash-table-set! ht "xY" 2)
+;;    (hash-table-set! ht "Xy" 1)
+;;    (hash-table-keys ht))
+;;
+;; My interpretation is that they can answer either ("Xy") or ("xY"),
+;; where `hash-table-values' will of course always answer (1), because
+;; the keys are the same according to the equivalence function.  In this
+;; implementation, both answer ("xY").  However, I don't guarantee that
+;; this won't change in the future.
+
+;;; Code:
+
+;;;; Module definition & exports
+
+(define-module (srfi srfi-69)
+  #:use-module (srfi srfi-1)	;alist-cons,second&c,assoc
+  #:use-module (srfi srfi-9)
+  #:use-module (srfi srfi-13)	;string-hash,string-hash-ci
+  #:use-module (ice-9 optargs)
+  #:export (;; Type constructors & predicate
+	    make-hash-table hash-table? alist->hash-table
+	    ;; Reflective queries
+	    hash-table-equivalence-function hash-table-hash-function
+	    ;; Dealing with single elements
+	    hash-table-ref hash-table-ref/default hash-table-set!
+	    hash-table-delete! hash-table-exists? hash-table-update!
+	    hash-table-update!/default
+	    ;; Dealing with the whole contents
+	    hash-table-size hash-table-keys hash-table-values
+	    hash-table-walk hash-table-fold hash-table->alist
+	    hash-table-copy hash-table-merge!
+	    ;; Hashing
+	    string-ci-hash hash-by-identity)
+  #:re-export (string-hash)
+  #:replace (hash))
+
+(cond-expand-provide (current-module) '(srfi-37))
+
+;;;; Hashing
+
+;;; The largest fixnum is in `most-positive-fixnum' in module (guile),
+;;; though not documented anywhere but libguile/numbers.c.
+
+(define (caller-with-default-size hash-fn)
+  "Answer a function that makes `most-positive-fixnum' the default
+second argument to HASH-FN, a 2-arg procedure."
+  (lambda* (obj #:optional (size most-positive-fixnum))
+    (hash-fn obj size)))
+
+(define hash (caller-with-default-size (@ (guile) hash)))
+
+(define string-ci-hash string-hash-ci)
+
+(define hash-by-identity (caller-with-default-size hashq))
+
+;;;; Reflective queries, construction, predicate
+
+(define-record-type srfi-69:hash-table
+  (make-srfi-69-hash-table real-table associator size weakness
+			   equivalence-function hash-function)
+  hash-table?
+  (real-table ht-real-table)
+  (associator ht-associator)
+  ;; required for O(1) by SRFI-69.  It really makes a mess of things,
+  ;; and I'd like to compute it in O(n) and memoize it because it
+  ;; doesn't seem terribly useful, but SRFI-69 is final.
+  (size ht-size ht-size!)
+  ;; required for `hash-table-copy'
+  (weakness ht-weakness)
+  ;; used only to implement hash-table-equivalence-function; I don't
+  ;; use it internally other than for `ht-associator'.
+  (equivalence-function hash-table-equivalence-function)
+  (hash-function hash-table-hash-function))
+
+(define (guess-hash-function equal-proc)
+  "Guess a hash function for EQUAL-PROC, falling back on `hash', as
+specified in SRFI-69 for `make-hash-table'."
+  (cond ((eq? equal? equal-proc) (@ (guile) hash)) ;shortcut most common case
+	((eq? eq? equal-proc) hashq)
+	((eq? eqv? equal-proc) hashv)
+	((eq? string=? equal-proc) string-hash)
+	((eq? string-ci=? equal-proc) string-ci-hash)
+	(else (@ (guile) hash))))
+
+(define (without-keyword-args rest-list)
+  "Answer REST-LIST with all keywords removed along with items that
+follow them."
+  (let lp ((acc '()) (rest-list rest-list))
+    (cond ((null? rest-list) (reverse! acc))
+	  ((keyword? (first rest-list))
+	   (lp acc (cddr rest-list)))
+	  (else (lp (cons (first rest-list) acc) (cdr rest-list))))))
+
+(define (guile-ht-ctor weakness)
+  "Answer the Guile HT constructor for the given WEAKNESS."
+  (case weakness
+    ((#f) (@ (guile) make-hash-table))
+    ((key) make-weak-key-hash-table)
+    ((value) make-weak-value-hash-table)
+    ((key-or-value) make-doubly-weak-hash-table)
+    (else (error "Invalid weak hash table type" weakness))))
+
+(define (equivalence-proc->associator equal-proc)
+  "Answer an `assoc'-like procedure that compares the argument key to
+alist keys with EQUAL-PROC."
+  (cond ((or (eq? equal? equal-proc)
+	     (eq? string=? equal-proc)) (@ (guile) assoc))
+	((eq? eq? equal-proc) assq)
+	((eq? eqv? equal-proc) assv)
+	(else (lambda (item alist)
+		(assoc item alist equal-proc)))))
+
+(define* (make-hash-table
+	  #:optional (equal-proc equal?)
+	  (hash-proc (guess-hash-function equal-proc))
+	  #:key (weak #f) #:rest guile-opts)
+  "Answer a new hash table using EQUAL-PROC as the comparison
+function, and HASH-PROC as the hash function.  See the reference
+manual for specifics, of which there are many."
+  (make-srfi-69-hash-table
+   (apply (guile-ht-ctor weak) (without-keyword-args guile-opts))
+   (equivalence-proc->associator equal-proc)
+   0 weak equal-proc hash-proc))
+
+(define (alist->hash-table alist . mht-args)
+  "Convert ALIST to a hash table created with MHT-ARGS."
+  (let* ((result (apply make-hash-table mht-args))
+	 (size (ht-size result)))
+    (with-hashx-values (hash-proc associator real-table) result
+      (for-each (lambda (pair)
+		  (let ((handle (hashx-get-handle hash-proc associator
+						  real-table (car pair))))
+		    (cond ((not handle)
+			   (set! size (1+ size))
+			   (hashx-set! hash-proc associator real-table
+				       (car pair) (cdr pair))))))
+		alist))
+    (ht-size! result size)
+    result))
+
+;;;; Accessing table items
+
+;; We use this to denote missing or unspecified values to avoid
+;; possible collision with *unspecified*.
+(define ht-unspecified (cons *unspecified* "ht-value"))
+
+;; I am a macro only for efficiency, to avoid varargs/apply.
+(define-macro (hashx-invoke hashx-proc ht-var . args)
+  "Invoke HASHX-PROC, a `hashx-*' procedure taking a hash-function,
+assoc-function, and the hash-table as first args."
+  `(,hashx-proc (hash-table-hash-function ,ht-var)
+		(ht-associator ,ht-var)
+		(ht-real-table ,ht-var)
+		. ,args))
+
+(define-macro (with-hashx-values bindings ht-var . body-forms)
+  "Bind BINDINGS to the hash-function, associator, and real-table of
+HT-VAR, while evaluating BODY-FORMS."
+  `(let ((,(first bindings) (hash-table-hash-function ,ht-var))
+	 (,(second bindings) (ht-associator ,ht-var))
+	 (,(third bindings) (ht-real-table ,ht-var)))
+     . ,body-forms))
+
+(define (hash-table-ref ht key . default-thunk-lst)
+  "Lookup KEY in HT and answer the value, invoke DEFAULT-THUNK if KEY
+isn't present, or signal an error if DEFAULT-THUNK isn't provided."
+  (let ((result (hashx-invoke hashx-ref ht key ht-unspecified)))
+    (if (eq? ht-unspecified result)
+	(if (pair? default-thunk-lst)
+	    ((first default-thunk-lst))
+	    (error "Key not in table" key ht))
+	result)))
+
+(define (hash-table-ref/default ht key default)
+  "Lookup KEY in HT and answer the value.  Answer DEFAULT if KEY isn't
+present."
+  (hashx-invoke hashx-ref ht key default))
+
+(define (hash-table-set! ht key new-value)
+  "Set KEY to NEW-VALUE in HT."
+  (let ((handle (hashx-invoke hashx-create-handle! ht key ht-unspecified)))
+    (if (eq? ht-unspecified (cdr handle))
+	(ht-size! ht (1+ (ht-size ht))))
+    (set-cdr! handle new-value))
+  *unspecified*)
+
+(define (hash-table-delete! ht key)
+  "Remove KEY's association in HT."
+  (with-hashx-values (h a real-ht) ht
+    (if (hashx-get-handle h a real-ht key)
+	(begin
+	  (ht-size! ht (1- (ht-size ht)))
+	  (hashx-remove! h a real-ht key))))
+  *unspecified*)
+
+(define (hash-table-exists? ht key)
+  "Return whether KEY is a key in HT."
+  (and (hashx-invoke hashx-get-handle ht key) #t))
+
+;;; `hashx-set!' duplicates the hash lookup, but we use it anyway to
+;;; avoid creating a handle in case DEFAULT-THUNK exits
+;;; `hash-table-update!' non-locally.
+(define (hash-table-update! ht key modifier . default-thunk-lst)
+  "Modify HT's value at KEY by passing its value to MODIFIER and
+setting it to the result thereof.  Invoke DEFAULT-THUNK for the old
+value if KEY isn't in HT, or signal an error if DEFAULT-THUNK is not
+provided."
+  (with-hashx-values (hash-proc associator real-table) ht
+    (let ((handle (hashx-get-handle hash-proc associator real-table key)))
+      (cond (handle
+	     (set-cdr! handle (modifier (cdr handle))))
+	    (else
+	     (hashx-set! hash-proc associator real-table key
+			 (if (pair? default-thunk-lst)
+			     (modifier ((car default-thunk-lst)))
+			     (error "Key not in table" key ht)))
+	     (ht-size! ht (1+ (ht-size ht)))))))
+  *unspecified*)
+
+(define (hash-table-update!/default ht key modifier default)
+  "Modify HT's value at KEY by passing its old value, or DEFAULT if it
+doesn't have one, to MODIFIER, and setting it to the result thereof."
+  (hash-table-update! ht key modifier (lambda () default)))
+
+;;;; Accessing whole tables
+
+(define (hash-table-size ht)
+  "Return the number of associations in HT.  This is guaranteed O(1)
+for tables where #:weak was #f or not specified at creation time."
+  (if (ht-weakness ht)
+      (hash-table-fold ht (lambda (k v ans) (1+ ans)) 0)
+      (ht-size ht)))
+
+(define (hash-table-keys ht)
+  "Return a list of the keys in HT."
+  (hash-table-fold ht (lambda (k v lst) (cons k lst)) '()))
+
+(define (hash-table-values ht)
+  "Return a list of the values in HT."
+  (hash-table-fold ht (lambda (k v lst) (cons v lst)) '()))
+
+(define (hash-table-walk ht proc)
+  "Call PROC with each key and value as two arguments."
+  (hash-table-fold ht (lambda (k v unspec) (proc k v) unspec)
+		   *unspecified*))
+
+(define (hash-table-fold ht f knil)
+  "Invoke (F KEY VAL PREV) for each KEY and VAL in HT, where PREV is
+the result of the previous invocation, using KNIL as the first PREV.
+Answer the final F result."
+  (hash-fold f knil (ht-real-table ht)))
+
+(define (hash-table->alist ht)
+  "Return an alist for HT."
+  (hash-table-fold ht alist-cons '()))
+
+(define (hash-table-copy ht)
+  "Answer a copy of HT."
+  (with-hashx-values (h a real-ht) ht
+    (let* ((size (hash-table-size ht)) (weak (ht-weakness ht))
+	   (new-real-ht ((guile-ht-ctor weak) size)))
+      (hash-fold (lambda (k v ign) (hashx-set! h a new-real-ht k v))
+		 #f real-ht)
+      (make-srfi-69-hash-table		;real,assoc,size,weak,equiv,h
+       new-real-ht a size weak
+       (hash-table-equivalence-function ht) h))))
+
+(define (hash-table-merge! ht other-ht)
+  "Add all key/value pairs from OTHER-HT to HT, overriding HT's
+mappings where present.  Return HT."
+  (hash-table-fold
+   ht (lambda (k v ign) (hash-table-set! ht k v)) #f)
+  ht)
+
+;;; srfi-69.scm ends here