Add draft version of multi-line grammar

README.md

@@ -16,3 +16,7 @@ To run the test suite, `pytest` is recommended, and can be done via:
 ```bash
 pytest -v --maxfail=1 larktools/tests/test_suite.py
 ```
+
+### Debugging
+
+For grammar development using an alternative, less optimized parsing strategy can help avoiding rule conflicts: Use `earley` instead of `lalr`

src/larktools/ebnf_grammar.py

@@ -15,7 +15,7 @@
 
   start: assign_var
 
-  assign_var: VARNAME "=" arith_expr 
+  assign_var: VARNAME "=" arith_expr
 
   variable: VARNAME ("[" INDEX "]")*
   VARNAME: LETTER (LETTER | DIGIT)*
@@ -26,6 +26,11 @@
   // but without the fancy tree shaping directives explained at 
   // https://lark-parser.readthedocs.io/en/stable/tree_construction.html
 
+
+  line: arith_expr
+
+  multi_line_block: (line _NL? | _NL )* 
+
   arith_expr: sum
   sum: product | addition | subtraction 
   addition: sum "+" product
@@ -57,4 +62,5 @@
 
   %import common.WS_INLINE
   %ignore WS_INLINE
+  %import common.NEWLINE -> _NL
 """

src/larktools/evaluation.py

@@ -109,6 +109,22 @@ def eval_bracketed_arith_expr(node, env):
     assert get_name(child) == "arith_expr"
     return eval_arith_expr(child, env)
 
+def eval_line(node, env):
+    # this is the content of a single line of input
+    child = get_children(node)[0]
+    child_name = get_name(child)
+    if child_name == "arith_expr":
+        return eval_arith_expr(child, env)
+
+def eval_multi_line_block(node, env):
+    # this can be either an arithmetic expression or 
+    # composed lines
+    children = get_children(node)
+    for child in children:
+        child_name = get_name(child)
+        assert child_name == "line"
+        res = eval_line(child, env)
+    return res
 
 def eval_variable(node, env):
     children = get_children(node)

tests/test_syntax.py

@@ -0,0 +1,32 @@
+import pytest
+from typing import Optional, Union
+
+from lark import Lark
+
+from larktools.ebnf_grammar import grammar
+from larktools.evaluation import eval_multi_line_block
+
+
+class SyntaxParser:
+    def __init__(self):
+        self.parser = Lark(grammar, parser="lalr", start="multi_line_block")
+        self.parse = self.parser.parse
+
+    def parse_and_eval(self, expression: str, env: Optional[Union[None, dict]] = None) -> Union[int, float]:
+        tree = self.parse(expression)
+        res = eval_multi_line_block(tree, {} if env is None else env)
+        return res
+
+
+def _parse_and_assert(expression: str, expected: Union[int, float]) -> None:
+    parser = SyntaxParser()
+    res = parser.parse_and_eval(expression)
+    assert expected == res
+
+def test_multi_line():
+    _parse_and_assert("5\n8", 8)
+    _parse_and_assert("\n\n\n8", 8)
+    _parse_and_assert("8\n\n\n", 8)
+    _parse_and_assert("5+5\n3+4\n1+2", 3)
+    _parse_and_assert("\n\n5\n\n3\n8", 8)
+