Examples: add import example

examples/lark_grammar.py

@@ -6,6 +6,9 @@ grammar_files = [
     'examples/python2.lark',
     'examples/python3.lark',
     'examples/lark.lark',
+    'examples/relative-imports/multiples.lark',
+    'examples/relative-imports/multiple2.lark',
+    'examples/relative-imports/multiple3.lark',
     'lark/grammars/common.lark',
 ]
 

examples/relative-imports/multiple2.lark

@@ -0,0 +1 @@
+start: ("0" | "1")* "0"

examples/relative-imports/multiple3.lark

@@ -0,0 +1,5 @@
+start: mod0mod0+
+
+mod0mod0: "0" | "1" mod1mod0
+mod1mod0: "1" | "0" mod2mod1 mod1mod0
+mod2mod1: "0" | "1" mod2mod1

examples/relative-imports/multiples.lark

@@ -0,0 +1,5 @@
+start: "2:" multiple2
+     | "3:" multiple3
+
+%import .multiple2.start -> multiple2
+%import .multiple3.start -> multiple3

examples/relative-imports/multiples.py

@@ -0,0 +1,28 @@
+#
+# This example demonstrates relative imports with rule rewrite
+# see multiples.lark
+#
+
+#
+# if b is a number written in binary, and m is either 2 or 3,
+# the grammar aims to recognise m:b iif b is a multiple of m
+#
+# for example, 3:1001 is recognised
+# because 9 (0b1001) is a multiple of 3
+#
+
+from lark import Lark, UnexpectedInput
+
+parser = Lark.open('multiples.lark', parser='lalr')
+
+def is_in_grammar(data):
+    try:
+        parser.parse(data)
+    except UnexpectedInput:
+        return False
+    return True
+
+for n_dec in range(100):
+    n_bin = bin(n_dec)[2:]
+    assert is_in_grammar('2:{}'.format(n_bin)) == (n_dec % 2 == 0)
+    assert is_in_grammar('3:{}'.format(n_bin)) == (n_dec % 3 == 0)