Work on PL/0 Grammar as a PEG example

extra/peg/pl0/authors.txt

@@ -0,0 +1 @@
+Chris Double

extra/peg/pl0/pl0-tests.factor

@@ -0,0 +1,13 @@
+! Copyright (C) 2007 Chris Double.
+! See http://factorcode.org/license.txt for BSD license.
+!
+USING: kernel tools.test peg peg.pl0 ;
+IN: temporary
+
+{ "abc" } [
+  "abc" 'ident' parse parse-result-ast 
+] unit-test
+
+{ 55 } [
+  "55abc" 'number' parse parse-result-ast 
+] unit-test

extra/peg/pl0/pl0.factor

@@ -0,0 +1,14 @@
+! Copyright (C) 2007 Chris Double.
+! See http://factorcode.org/license.txt for BSD license.
+USING: kernel arrays strings math.parser peg ;
+IN: peg.pl0
+
+#! Grammar for PL/0 based on http://en.wikipedia.org/wiki/PL/0
+
+: 'ident' ( -- parser )
+  CHAR: a CHAR: z range 
+  CHAR: A CHAR: Z range 2array choice repeat1 
+  [ >string ] action ;
+
+: 'number' ( -- parser )
+  CHAR: 0 CHAR: 9 range repeat1 [ string>number ] action ;

extra/peg/pl0/summary.txt

@@ -0,0 +1 @@
+Grammar for PL/0 Language