Implement ldict-ref.

doc/utils.md

@@ -62,6 +62,17 @@ Returns ```#t``` if given dictionary contains no keys.
 
 Returns ```#t``` if given ```ld``` contains given key ```k```.
 
+    (ldict-ref ld k [default])
+
+* ```ld``` - a ldict instance
+* ```k``` - a compatible key
+* ```default``` - optional fallback value
+
+Retrieves the value associated with given key in given dictionary. If
+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.
+
 ### IO
 
     (import util-io)

src/util-dict.scm

@@ -97,13 +97,16 @@
  ;; is provided it is used as default value in case the key does not
  ;; exist. If only two arguments are given and the key does not exist,
  ;; raises an error.
- (define (dict-ref d k . r)
-   (let ((p (assq k d)))
-     (if p
-	 (cdr p)
-	 (if (null? r)
-	     (error 'dict-ref "Key does not exist" k)
-	     (car r)))))
+ (define (ldict-ref ld k . ds)
+   (let ((equality? (ldict-equality? ld)))
+     (let loop ((pairs (ldict-pairs ld)))
+       (if (null? pairs)
+	   (if (null? ds)
+	       (error 'ldict-ref "Key does not exist" k)
+	       (car ds))
+	   (if (equality? (caar pairs) k)
+	       (cdar pairs)
+	       (loop (cdr pairs)))))))
 
  ;; Returns a new dictionary based on d with key k removed. If it
  ;; doesn't contain the key, an error is raised.