added <<conditionally

2 files changed, 11 insertions, 1 deletions

diff --git a/package.lisp b/package.lisp
index efd3e50..086fa0d 100644
--- a/package.lisp
+++ b/package.lisp
@@ -15,6 +15,7 @@
    #:<<char
    #:<<char-brackets
    #:<<char-equal
+   #:<<conditionally
    #:<<cons
    #:<<cons-map
    #:<<counting
diff --git a/parzival.lisp b/parzival.lisp
index cc88725..71bb6c0 100644
--- a/parzival.lisp
+++ b/parzival.lisp
@@ -54,7 +54,7 @@ and the thrid value is the stream stream.  The stream will be left in
 whatever state it was in when the parse stopped, either successfully
 or not."
   `(progn
-     (defvar ,name ',name)
+     (defparameter ,name ',name)
      (defun ,name (stream) ,docstring (funcall ,parser stream))))
 
 
@@ -116,6 +116,15 @@ in then. If the parse fails the combinator else is run instead."
   `(<<if (,var ,parser ,stream) ,form <fail<))
 
 
+(defmacro <<conditionally (condition then else)
+  "Returns a parser that is sensative to the current state.  If
+CONDITION is true, then the THEN parser is run, otherwise the ELSE parser is run."
+  `(lambda (stream)
+     (if ,condition
+         (funcall ,then stream)
+         (funcall ,else stream))))
+
+
 ;;; The <<PLUS COMBINATOR is vital, and gives us amazing powers to choose our
 ;;; own future!  This section defines <<plus and uses it to define some nice utilities.