The beginning of the parser monads.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/org/gnu/clojure/gnunet/parser.clj b/src/org/gnu/clojure/gnunet/parser.clj
new file mode 100644
index 0000000..c89876a
--- /dev/null
+++ b/src/org/gnu/clojure/gnunet/parser.clj
@@ -0,0 +1,18 @@
+(ns org.gnu.clojure.gnunet.parser
+  (:use clojure.contrib.monads))
+
+(def parser-m (state-t maybe-m))
+
+(defn item
+  "Parser which returns the first item of input."
+  [xs]
+  (when (not (empty? xs)) [(first xs) (rest xs)]))
+
+(defn items
+  "Produces a parser that returns the first n items of input."
+  [n]
+  (with-monad parser-m
+    (m-when (> n 0)
+      (domonad [x item
+                xs (items (- n 1))]
+        (cons x xs)))))
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