class Compiler():
#valid token types which can comprise a <Statement>
valid_statement_tokens = [
Token.LBLOCK, Token.VAR, Token.CONST, Token.IDENTIFIER, Token.IF,
Token.INPUT, Token.OUTPUT, Token.WHILE, Token.SEMI]
#valid token types which can comprise an <Expression>
valid_expression_tokens = [
Token.NUMBER, Token.IDENTIFIER, Token.LPAREN, Token.RPAREN,
Token.PLUS, Token.MINUS, Token.DIV, Token.MUL, Token.TRUE, Token.FALSE]
#valid token types which can comprise a <Comparison> token
valid_comparison_tokens = [
Token.LTEQ, Token.GTEQ, Token.GT,
Token.LT, Token.EQUAL, Token.NOTEQUAL]
def __init__(self, tokens):
"""
Compiler initializer.
tokens (list): Tokens produced by the parser
"""
self.tokens = tokens
self.compiled = list() #compiled code generated by run()
def run(self):
"""
Compiles the code
"""
if len(self.tokens) == 0: #case when the program is empty
self.compiled = ['.']
return
preserved_tokens = self.tokens[:] #preserve the tokens because they're consumed during compilation
self.program = Program(self).build() #begin recursive descent parsing
self.tokens = preserved_tokens #restore the tokens
self.program.clean() #begin the recursive clean/modification process (to translate to PL/0)
self.program.compile() #generate the compiled PL/0 code
def error(self, text):
"""
The compiler found a grammar error and will report it to the user. All errors are fatal
text (string): Error message to report to user.
"""
quit('LINE ' + str(self.tokens[0].line) + ' (Token: "' + self.tokens[0].text + '") ERROR <' + callee().lstrip('_').upper() + '> : ' + text)
def next(self, pos = 0):
"""
Return the type of token pos positions ahead in the token list.
pos (int, optional): The position to lookup within the tokens.
"""
return "<NONE>" if len(self.tokens) <= pos else self.tokens[pos].type
def skip(self, pos = 1):
"""
Tell the compiler to skip/discard pos number of tokens.
pos (int, optional): The number of tokens to skip/discard.
"""
self.tokens = self.tokens[pos:]
def __str__(self):
"""
String representation of the compiler
"""
return ''.join([str(i) for i in self.compiled])
