Implement ldict-remove procedure.

doc/utils.md

@@ -73,6 +73,14 @@ the dictionary does not contain it and no default is given, an
 exception is raised. Otherwise the default value is returned in case
 of missing key.
 
+    (ldict-remove ld k)
+
+* ```ld``` - a ldict instance
+* ```k``` - a compatible key
+
+Returns a new dictionary with the record under given key removed. If
+the dictionary does not contain the key ```k```, an error is raised.
+
 ### IO
 
     (import util-io)

src/util-dict.scm

@@ -110,17 +110,21 @@
 
  ;; Returns a new dictionary based on d with key k removed. If it
  ;; doesn't contain the key, an error is raised.
- (define (dict-remove d k)
-   (let loop ((s d)
-	      (r '())
-	      (e #t))
-     (if (null? s)
-	 (if e
-	     (error 'dict-remove "Key does not exist" k)
-	     r)
-	 (if (eq? (caar s) k)
-	     (loop (cdr s) r #f)
-	     (loop (cdr s) (cons (car s) r) e)))))
+ (define (dict-remove ld k)
+   (let ((equality? (ldict-equality? ld)))
+     (let loop ((pairs (ldict-pairs ld))
+		(res '())
+		(failure #t))
+       (if (null? pairs)
+	   (if failure
+	       (error 'dict-remove "Key does not exist" k)
+	       (cons TAG-LDICT
+		     (cons (ldict-meta ld)
+			   res)))
+	   (loop (cdr pairs)
+		 (if (equality? (caar pairs) k)
+		     res
+		     (cons (car pairs) res)))))))
 
  ;; Adds a new value v under the key k to the dictionary d possibly
  ;; overwriting any value which has been stored under the key