chapter 5: challenge 3 done

pylox/util/rpn_ast_printer.py

@@ -0,0 +1,21 @@
+import pylox.expr as ast
+
+
+# Define a visitor class for our syntax tree classes that takes an expression,
+# converts it to RPN, and returns the resulting string.
+class RpnAstPrinter(ast.ExprVisitor):
+
+    def print_expr(self, expr: ast.Expr):
+        return expr.accept(self)
+
+    def visit_binary_expr(self, expr: ast.Binary):
+        return f'{str(expr.left.accept(self))} {str(expr.right.accept(self))} {expr.operator.lexeme}'
+
+    def visit_grouping_expr(self, expr: ast.Grouping):
+        return expr.expr.accept(self)
+
+    def visit_literal_expr(self, expr: ast.Literal):
+        return str(expr.value)
+
+    def visit_unary_expr(self, expr: ast.Unary):
+        return f'{str(expr.right.accept(self))} {expr.operator.lexeme}'

tests/test_ast.py

@@ -1,11 +1,13 @@
 from pylox.util.ast_printer import AstPrinter
+from pylox.util.rpn_ast_printer import RpnAstPrinter
 from pylox.scanner import Token, TokenType
 import pylox.expr as ast
 
 
 # example from http://www.craftinginterpreters.com/representing-code.html#a-not-very-pretty-printer
 def test_if_ast_printer_works_correct() -> None:
     # GIVEN
+    # -123 * (45.67)
     expression = ast.Binary(
         ast.Unary(
             Token(TokenType.MINUS, "-", None, 1),
@@ -18,3 +20,24 @@ def test_if_ast_printer_works_correct() -> None:
 
     # THEN
     assert result == "(* (- 123) (group 45.67))"
+
+
+# challenge 3 from http://www.craftinginterpreters.com/representing-code.html#challenges
+def test_if_rpn_ast_printer_works_correct() -> None:
+    # GIVEN
+    # (1 + 2) * (4 - 3)
+    expression = ast.Binary(
+        ast.Grouping(
+            ast.Binary(ast.Literal(1),
+                       Token(TokenType.PLUS, "+", None, 1),
+                       ast.Literal(2))),
+        Token(TokenType.STAR, "*", None, 1),
+        ast.Grouping(
+            ast.Binary(ast.Literal(4),
+                       Token(TokenType.MINUS, "-", None, 1),
+                       ast.Literal(3)))
+    )
+    # WHEN
+    result = RpnAstPrinter().print_expr(expression)
+    # THEN
+    assert result == "1 2 + 4 3 - *"

tools/generate_ast.py

@@ -5,20 +5,23 @@ def define_ast(base_name, types):
     # TODO: Add output directory handling
     path = "../pylox/" + base_name.lower() + ".py"
     file = open(path, "w")
-
+    # HEADER
     file.write("# THIS CODE IS GENERATED AUTOMATICALLY. DO NOT CHANGE IT MANUALLY!\n\n")
-
+    # IMPORTS
     file.write('import typing\n')
     file.write('from abc import ABC, abstractmethod\n\n')
     file.write('from pylox.tokens import Token\n')
+    # VISITOR
     define_visitor(file, base_name, types)
+    # BASE CLASS
     file.write(f'class {base_name}:\n')
     file.write(f'{TAB}def __init__(self):\n')
     file.write(f'{TAB * 2}pass\n')
     file.write(f'{TAB}@abstractmethod\n')
     file.write(f'{TAB}def accept(self, visitor : {base_name}Visitor):\n')
     file.write(f'{TAB * 2}pass')
     file.write('\n')
+    # IMPLEMENTATIONS
     for className, fields in types.items():
         file.write('\n')
         define_type(file, base_name, className, fields)