Implement new ldict-set procedure.

doc/utils.md

@@ -81,6 +81,15 @@ of missing 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.
 
+    (ldict-set ld k v)
+
+* ```ld``` - a ldict instance
+* ```k``` - a compatible key
+* ```v``` - a value to insert
+
+Sets existing key ```k``` to the new value ```v``` or inserts it if it
+is not already present in the dictionary ```ld```.
+
 ### IO
 
     (import util-io)

src/util-dict.scm

@@ -110,7 +110,7 @@
 
  ;; 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 ld k)
+ (define (ldict-remove ld k)
    (let ((equality? (ldict-equality? ld)))
      (let loop ((pairs (ldict-pairs ld))
 		(res '())
@@ -129,16 +129,19 @@
  ;; Adds a new value v under the key k to the dictionary d possibly
  ;; overwriting any value which has been stored under the key
  ;; before. Returns the updated dictionary.
- (define (dict-set d k v)
+ (define (ldict-set ld k v)
-   (let ((dr (let loop ((s d)
+   (let ((equality? (ldict-equalit? ld)))
-			(r '()))
+     (let loop ((pairs (ldict-pairs ld))
-	       (if (null? s)
+		(res '()))
-		   r
+       (if (null? pairs)
-		   (if (eq? (caar s) k)
+	   (cons TAG-LDICT
-		       (loop (cdr s) r)
+		 (cons (ldict-meta ld)
-		       (loop (cdr s) (cons (car s) r)))))))
 		       (cons (cons k v)
-	   dr)))
+			     res)))
+	   (loop (cdr pairs)
+		 (if (equality? (caar pairs) k)
+		     res
+		     (cons (car pairs) res)))))))
 
  ;; Returns the list of keys stored in given dictionary.
  (define (dict-keys d)