...

is there any reason why float parses only positive numbers?

It is usual in parsing libraries to separate the recognition of a leading sign from recognition of the number itself: the sign-only parser can be reused in many contexts, e.g. in the Haskell'98 Numeric library, there is readSigned :: Real a => ReadS a -> ReadS a which takes a secondary parser as its argument. You can instantiate that argument to any of readDec :: Num a => ReadS a readHex :: Num a => ReadS a readFloat :: Num a => ReadS a etc. I do not know if the equivalent of "readSigned" exists in Parsec, but it in polyparse's Text.Parse module, it is called "parseSigned", rather unsurprisingly. Regards, Malcolm