added example grammar_building.py

examples/advanced/grammar_building.py

@@ -0,0 +1,59 @@
+from pathlib import Path
+
+from lark.indenter import Indenter
+from lark.lark import Lark
+from lark.load_grammar import GrammarBuilder
+
+MATCH_GRAMMAR = ('match', """
+
+%extend compound_stmt: match_stmt
+
+match_stmt: "match" test ":" cases
+
+cases: _NEWLINE _INDENT case+ _DEDENT
+
+case: "case" test ":" suite // test is not quite correct. 
+
+""", ('compound_stmt', 'test', 'suite', '_DEDENT', '_INDENT', '_NEWLINE'))
+
+EXTENSIONS = (MATCH_GRAMMAR,)
+
+builder = GrammarBuilder()
+
+builder.load_grammar((Path(__file__).with_name('python3.lark')).read_text(), 'python3')
+
+for name, ext_grammar, needed_names in EXTENSIONS:
+    mangle = builder.get_mangle(name, dict(zip(needed_names, needed_names)))
+    builder.load_grammar(ext_grammar, name, mangle)
+
+grammar = builder.build()
+
+
+class PythonIndenter(Indenter):
+    NL_type = '_NEWLINE'
+    OPEN_PAREN_types = ['LPAR', 'LSQB', 'LBRACE']
+    CLOSE_PAREN_types = ['RPAR', 'RSQB', 'RBRACE']
+    INDENT_type = '_INDENT'
+    DEDENT_type = '_DEDENT'
+    tab_len = 8
+
+
+parser = Lark(grammar, parser='lalr', start=['single_input', 'file_input', 'eval_input'], postlex=PythonIndenter())
+
+tree = parser.parse(r"""
+
+a = 5
+
+def name(n):
+    match n:
+        case 1:
+            print("one")
+        case 2:
+            print("two")
+        case _:
+            print("number is to big") 
+
+name(a)
+""", start='file_input')
+
+print(tree.pretty())

lark-stubs/reconstruct.pyi

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 
-from typing import List, Dict, Union
+from typing import List, Dict, Union, Callable
 from .lark import Lark
 from .tree import Tree
 from .visitors import Transformer_InPlace
@@ -30,7 +30,7 @@ class MakeMatchTree:
 
 class Reconstructor:
 
-    def __init__(self, parser: Lark, term_subs: Dict[str, str] = ...):
+    def __init__(self, parser: Lark, term_subs: Dict[str, Callable[[str], str]] = ...):
         ...
 
     def reconstruct(self, tree: Tree) -> str: