def _parse(tokenIter):
""" _parse() recursively extract the expression from the given
token iterator
//param tokenIter is the token iterator that represents the
stream of tokens
//return a pair, where the first parameter reports the error code
occurs while parsing (OK indicates no error happens);
the second parameter is the extracted expression, which will
be None if error occurs.
"""
try:
token = tokenIter.next()
except StopIteration:
return ParseError.TOKEN_NORMALLY_ENDS, None
# Token type is ERROR
if token.tokenType == Tokens.ERROR:
return ParseError.TOKENIZE_ERROR, token
# All tokens, except the special characters, are considered. special char are: ( ) '
if not token.tokenType in Tokens.specialCharacters:
return ParseError.OK, Value.makeFromToken(token)
# check if this is the end of an expression
if token.tokenType == Tokens.RPAREN:
return ParseError.CE_ENDS, token
"""
# If the token either indicates the expression element
# (operator, parameters)nor the end of expression, then it
# must be the "beginning" of a expression.
if token.tokenType != Tokens.LPAREN:
return ParseError.EXPECT_LPAREN, token
"""
if token.tokenType == Tokens.QUOTE:
error, result = _parse(tokenIter)
return ParseError.OK, Value.makeLiteral(result)
sList = []
# Read parameters, operator is placed together with parameter as the first element of the list
while True:
error, param = _parse(tokenIter)
if error != ParseError.OK:
# reach the end the this expression?
if error == ParseError.CE_ENDS:
break
elif error == ParseError.TOKEN_NORMALLY_ENDS:
return ParseError.TOKEN_UNEXPECTED_ENDS, None #position: the end of the expression
# or real error occurs
else:
return error, param
sList.append(param)
return ParseError.OK, Value.makeList(sList)
