diff --git a/brmsaptool.scm b/brmsaptool.scm
index 9f7a8d6..90a7d90 100644
--- a/brmsaptool.scm
+++ b/brmsaptool.scm
@@ -57,12 +57,18 @@
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Dictionary
 
+;; Returns an empty dictionary represented as empty list.
 (define (make-dict)
   '())
 
+;; Checks whether given dictionary d contains the key k.
 (define (dict-has-key? d k)
   (if (assq k d) #t #f))
 
+;; Retrieves the value for key k from dictionary d. If third argument
+;; 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
@@ -71,6 +77,8 @@
 	    (error 'dict-ref "Key does not exist" k)
 	    (car r)))))
 
+;; 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 '())
@@ -83,6 +91,9 @@
 	    (loop (cdr s) r #f)
 	    (loop (cdr s) (cons (car s) r) e)))))
 
+;; 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)
   (let ((dr (let loop ((s d)
 		       (r '()))
@@ -94,6 +105,7 @@
     (cons (cons k v)
 	  dr)))
 
+;; Returns the list of keys stored in given dictionary.
 (define (dict-keys d)
   (map car d))