def while_statement(token):
"""
Implements recursive descent for the rule:
<while_statement> ==>
34 TokenType.KeywordWhile TokenType.OpenParen <expression>
TokenType.CloseParen <code_block>
"""
if token.t_type == TokenType.KeywordWhile:
print(34, end=" ")
before_while_lbl, after_while_lbl = CG.gen_label("while")
# Write label for beginning of while loop
CG.code_gen_label(before_while_lbl)
Parser.match(token, TokenType.KeywordWhile)
Parser.match(token, TokenType.OpenParen)
er_condition = Parser.expression(token)
Parser.match(token, TokenType.CloseParen)
# Perform the test
CG.code_gen_if(er_condition, after_while_lbl)
# Write the contents of the loop
Parser.code_block(token)
# Branch back to the test again
CG.code_gen("b", before_while_lbl)
# Write label for end of while loop, to pick up when the test fails
CG.code_gen_label(after_while_lbl)
else:
Parser.raise_production_not_found_error(token, 'while_statement')
def if_statement(token):
"""
Implements recursive descent for the rule:
<if_statement> ==>
31 TokenType.KeywordIf TokenType.OpenParen <expression>
TokenType.CloseParen <code_block> [ <else_clause> ]
"""
if token.t_type == TokenType.KeywordIf:
print(31, end=" ")
Parser.match(token, TokenType.KeywordIf)
Parser.match(token, TokenType.OpenParen)
er_condition = Parser.expression(token)
if er_condition.data_type != DataTypes.BOOL:
raise SemanticError(
"If statement requires boolean expression "
"as an argument", Parser.file_reader.get_line_data())
Parser.match(token, TokenType.CloseParen)
else_label, after_else_label = CG.gen_label("else")
CG.code_gen_if(er_condition, else_label)
Parser.code_block(token)
if token.t_type == TokenType.KeywordElse:
Parser.match(token, TokenType.KeywordElse)
# the last code block must branch to after the else clause
CG.code_gen("b", after_else_label)
# if test failed, then pick up program execution here
CG.code_gen_label(else_label)
# generate the else block
Parser.code_block(token)
# make the after_else label
CG.code_gen_label(after_else_label)
else:
# if test failed, then pick up program execution here
CG.code_gen_label(else_label)
else:
Parser.raise_production_not_found_error(token, 'if_statement')