branch: master
commit cbd33529b83fc55967153887f273dc9c84a328c3
Author: Junpeng Qiu <qjpchm...@gmail.com>
Commit: Junpeng Qiu <qjpchm...@gmail.com>
Add parsec-lookahead
---
parsec-tests.el | 29 +++++++++++++++++++++++++++++
parsec.el | 7 +++++++
2 files changed, 36 insertions(+)
diff --git a/parsec-tests.el b/parsec-tests.el
index fdf2055..e9c2672 100644
--- a/parsec-tests.el
+++ b/parsec-tests.el
@@ -229,6 +229,35 @@
(parsec-str "abc")))
"abc")))
+(ert-deftest test-parsec-lookahead ()
+ (should
+ (equal
+ (parsec-with-input "abc"
+ (parsec-lookahead (parsec-str "abc"))
+ (point))
+ (point-min)))
+ (should
+ (equal
+ (parsec-with-input "abc"
+ (parsec-start
+ (parsec-lookahead
+ (parsec-and
+ (parsec-ch ?a)
+ (parsec-ch ?c))))
+ (point))
+ (1+ (point-min))))
+ (should
+ (equal
+ (parsec-with-input "abc"
+ (parsec-start
+ (parsec-try
+ (parsec-lookahead
+ (parsec-and
+ (parsec-ch ?a)
+ (parsec-ch ?c)))))
+ (point))
+ (point-min))))
+
(ert-deftest test-parsec-error-handles ()
(should
(equal
diff --git a/parsec.el b/parsec.el
index 70209e8..f28e42c 100644
--- a/parsec.el
+++ b/parsec.el
@@ -730,6 +730,13 @@ point of your parsing program."
(parsec-and ,parser)
(goto-char ,orig-pt-sym)))))
+(defmacro parsec-lookahead (parser)
+ "Try PARSER, and pretend that no input is consumed when it succeeds."
+ (let ((orig-pt-sym (make-symbol "orig-pt")))
+ `(let ((,orig-pt-sym (point)))
+ (parsec-return ,parser
+ (goto-char ,orig-pt-sym)))))
+
(defsubst parsec--atom-tag (name)
(intern (format "parsec-failed-at-half-%s" name)))
