reads [Standard lab question]

[David Sands]

A question about the standard lab came in:

In Part I, a hint says that we should use reads :: [(Double,String)] for

parsing floating point values, but we have no idea how to use that with

an unmodified version of Parsing.hs, because you have to pass the whole

unparsed string to reads, which is not accessible for a Parser. 

If you look at the API for Parsing 

http://www.cse.chalmers.se/edu/course/TDA452/FPLectures/doc/Parsing.html

then you find

readsP :: Read a => Parser a

A parser for anything in the Read class satisfying

parse readsP s == listToMaybe (reads s)