lex ['I':'n':'t':rest] = (Right IntTypeToken, rest)
lex ['C':'h':'a':'r':rest] = (Right CharTypeToken, rest)
lex ['B':'o':'o':'l':rest] = (Right BoolTypeToken, rest)
lex ['I':'n':'t':rest] = (Right IntTypeToken, rest)
lex ['C':'h':'a':'r':rest] = (Right CharTypeToken, rest)
lex ['B':'o':'o':'l':rest] = (Right BoolTypeToken, rest)