[Haskell-beginners] questions about "Write yourself a Scheme in 48 hours"

I'm working through "Write yourself a Scheme in 48 hours". I'm on the parsing section http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours/Parsing and I have a question about the following function parseNumber :: Parser LispVal parseNumber = liftM (Number . read) $ many1 digit digit looks like a variable, but I don't see it mentioned anywhere. Where is the input coming from? Is this an example of partial application?