Ignore whitespace when tokenizing
Would be sad if I lost my TODO file
Extract tokenizing rules for double character tokens
Throw exception when the tokenizer does not make progress
Throw exception when the tokenizer can not match quote characters
Throw exception when an unexpected token appears
Throw exception when the right-hand side of a binary operation is missing
Throw exception when a predicate is empty
Throw exception when a path expression ends in a slash
Throw exception when the right-hand side of a unary operation is missing
Enforce that the token after a variable reference is a string