Pretty print parser-input

1 files changed, 9 insertions, 0 deletions

diff --git a/input.lisp b/input.lisp
index 100baa5..15b8e08 100644
--- a/input.lisp
+++ b/input.lisp
@@ -29,3 +29,12 @@
            (setf column 1))
           (t (incf column)))))
     (values line column)))
+
+(defmethod print-object ((obj parser-input) stream)
+  (let ((context-length 10))
+    (let ((begin (max (- (input-cursor obj) context-length) 0))
+          (end (min (+ (input-cursor obj) context-length) (length (input-data obj)))))
+      (format stream "...~a~a~a..."
+              (substitute #\¶ #\Newline (subseq (input-data obj) begin (input-cursor obj)))
+              (substitute #\¶ #\Newline (subseq (input-data obj) (input-cursor obj) (1+ (input-cursor obj))))
+              (substitute #\¶ #\Newline (subseq (input-data obj) (1+ (input-cursor obj)) end))))))