Allow merging lines by backspacing at the beginning of a line

sloth/editor.scm

@@ -99,12 +99,22 @@
    (string-take s k)
    (string-drop s (1+ k))))
 
+;;; merges k and k+1
+(define (merge-lines buffer k)
+  (append (list-head buffer k)
+          (list
+           (string-append (list-ref buffer k)
+                          (list-ref buffer (1+ k))))
+          (list-tail buffer (+ k 2))))
+
 (define (backward-delete-char state)
   (define buf (buffer state))
   (define x (curx state))
   (define y (cury state))
-  (list-set! buf y
-             (string-delete-kth (list-ref buf y) (1- x)))
+  (if (> x 0)
+      (list-set! buf y
+                 (string-delete-kth (list-ref buf y) (1- x)))
+      (set! (buffer state) (merge-lines buf (1- y))))
   (move-cursor state #:x -1 #:relative? #t))
 
 (define (delete-char state)