src/parser/parser-proto.lisp: Add functions returning standard parsers.

[sod] / src / parser / parser-proto.lisp

diff --git a/src/parser/parser-proto.lisp b/src/parser/parser-proto.lisp
index 189e503..7aafe45 100644 (file)
--- a/src/parser/parser-proto.lisp
+++ b/src/parser/parser-proto.lisp
@@ -87,6 +87,21 @@
          failures
          :initial-value nil))
 
+(export 'parse-empty)
+(defun parse-empty (&optional value)
+  "Return a parser which parses nothing, successfully.
+
+   The parser returns VALUE and consumes nothing."
+  (lambda () (values value t nil)))
+
+(export 'parse-fail)
+(defun parse-fail (indicator &optional consumedp)
+  "Return a parser which fails.
+
+   The parser reports the INDICATOR and (falsely) claims to have consumed
+   input if CONSUMEDP is true."
+  (lambda () (values indicator nil consumedp)))
+
 ;;;--------------------------------------------------------------------------
 ;;; Basic protocol.