par: piece-table: make and index

1 files changed, 20 insertions, 6 deletions

diff --git a/par/piece-table.scm b/par/piece-table.scm
index d6a3c4e..6876541 100644
--- a/par/piece-table.scm
+++ b/par/piece-table.scm
@@ -17,18 +17,34 @@
 ;; The piece table itself;
 ;; original and add are strings and pieces is a list of pieces
 (define-record-type <piece-table>
-  (make-piece-table original add pieces)
+  (%make-piece-table original add pieces)
   piece-table?
   (original piece-table-original set-piece-table-original!)
   (add piece-table-add set-piece-table-add!)
   (pieces piece-table-pieces set-piece-table-pieces!))
 
+(define %DEFAULT-ADD-BUFFER-LENGTH 1024)
+
+(define (make-piece-table original)
+  (%make-piece-table
+    original
+    (make-string %DEFAULT-ADD-BUFFER-LENGTH)
+    (list (make-piece original 0 (string-length original) 'normal))))
+
 (define (add-piece-table-piece! piece-table piece)
-  (cons piece (piece-table-pieces piece-table)))
+  (append (piece-table-pieces piece-table) (list piece)))
 
 
 (define (piece-table-index piece-table pos)
-  #f)
+  (let loop ((pieces (piece-table-pieces piece-table))
+             (start 0))
+    (let* ((piece (car pieces))
+           (end   (piece-length piece)))
+      (if (<= start pos (- end 1))
+        (string-ref (piece-buffer piece) (+ start pos))
+        (if (not (null? (cdr pieces)))
+          (loop (cdr pieces) (+ start end))
+          (eof-object))))))
 
 (define (piece-table-insert! piece-table pos char)
   #f)
@@ -49,9 +65,7 @@
 
 
 ;; From/to string
-(define (string->piece-table string)
-  (make-piece-table string ""
-    (list (make-piece string 0 (string-length string) 'normal))))
+(define string->piece-table make-piece-table)
 
 (define (piece-table->string piece-table)
   #f)