First advances to lookahead implementation

1 files changed, 10 insertions, 5 deletions

diff --git a/input.lisp b/input.lisp
index 3e646b4..4f803ec 100644
--- a/input.lisp
+++ b/input.lisp
@@ -5,17 +5,22 @@
   (file nil :read-only t)
   (data nil :read-only t))
 
-(defun has-data? (input)
-  (< (input-cursor input)
+(defun has-data? (input &optional (window-size 1))
+  (< (+ window-size -1 (input-cursor input))
      (length (input-data input))))
 
-(defun element (input)
+(defun peek-1 (input)
   (char (input-data input)
         (input-cursor input)))
 
-(defun advance (input)
+(defun peek-n (input window-size)
+  (subseq (input-data input)
+          (input-cursor input)
+          window-size))
+
+(defun advance (input &optional (amount 1))
   (let ((new-input (copy-structure input)))
-    (incf (input-cursor new-input))
+    (incf (input-cursor new-input) amount)
     new-input))
 
 (declaim (ftype (function (simple-string) (values input &optional)) from-string))