symtab05.py

from spi import Lexer, Parser, NodeVisitor, BuiltinTypeSymbol, VarSymbol


class SymbolTable(object):
    def __init__(self):
        self._symbols = {}
        self._init_builtins()

    def _init_builtins(self):
        self.insert(BuiltinTypeSymbol('INTEGER'))
        self.insert(BuiltinTypeSymbol('REAL'))

    def __str__(self):
        symtab_header = 'Symbol table contents'
        lines = ['\n', symtab_header, '_' * len(symtab_header)]
        lines.extend(
            ('%7s: %r' % (key, value))
            for key, value in self._symbols.items()
        )
        lines.append('\n')
        s = '\n'.join(lines)
        return s

    __repr__ = __str__

    def insert(self, symbol):
        print('Insert: %s' % symbol.name)
        self._symbols[symbol.name] = symbol

    def lookup(self, name):
        print('Lookup: %s' % name)
        symbol = self._symbols.get(name)
        # 'symbol' is either an instance of the Symbol class or None
        return symbol


class SemanticAnalyzer(NodeVisitor):
    def __init__(self):
        self.symtab = SymbolTable()

    def visit_Block(self, node):
        for declaration in node.declarations:
            self.visit(declaration)
        self.visit(node.compound_statement)

    def visit_Program(self, node):
        self.visit(node.block)

    def visit_Compound(self, node):
        for child in node.children:
            self.visit(child)

    def visit_NoOp(self, node):
        pass

    def visit_BinOp(self, node):
        self.visit(node.left)
        self.visit(node.right)

    def visit_VarDecl(self, node):
        type_name = node.type_node.value
        type_symbol = self.symtab.lookup(type_name)

        # We have all the information we need to create a variable symbol.
        # Create the symbol and insert it into the symbol table.
        var_name = node.var_node.value
        var_symbol = VarSymbol(var_name, type_symbol)
        self.symtab.insert(var_symbol)

    def visit_Assign(self, node):
        # right-hand side
        self.visit(node.right)
        # left-hand side
        self.visit(node.left)

    def visit_Var(self, node):
        var_name = node.value
        var_symbol = self.symtab.lookup(var_name)
        if var_symbol is None:
            raise Exception(
                "Error: Symbol(identifier) not found '%s'" % var_name
            )


if __name__ == '__main__':
    text = """
program SymTab5;
    var x : integer;

begin
    x := y;
end.
"""
    lexer = Lexer(text)
    parser = Parser(lexer)
    tree = parser.parse()

    semantic_analyzer = SemanticAnalyzer()
    try:
        semantic_analyzer.visit(tree)
    except Exception as e:
        print(e)

    print(semantic_analyzer.symtab)