Hello! On Tue, Oct 10, 2000 at 08:11:08PM +0100, Graeme Turner wrote:
I have a file of the following format :-
Surname , Forename , Age , Height e.g. <String>, <String>, <Int> , <Int>
I have a tuple called Person which is defined as (String,String,Int,Int) as you would expect.
What I want to do is to create a function which will 1 take a line from the file 2 create a Person tuple from the read information
Don't think TOO imperatively. type Record = (String {- surname -}, String {- forename -}, Int {- age -}, Int {- height -} Now write a function that parses one line into that record. First a helper: Remove leading and trailing whitespace from a string: import Char (isSpace) cleanup :: String -> String cleanup = reverse . dropWhile isSpace . reverse . dropWhile isSpace -- Think about it! parseLine :: String -> Record parseLine s = (surName, foreName, age, height) where isComma = (',' ==) (surname', rest0) = break isComma s surname = cleanup surname' -- the tail removes the , (foreName', rest1) = break isComma $ tail rest0 foreName = cleanup foreName' (ageString, rest2) = break isComma $ tail rest1 age = read ageString heightString = tail rest2 -- remove , height = read heightString Then, use that together with my previous mail: import List(sort) showRecord :: Record -> String -- please do at least that for yourself. Mind ++ for string (in fact any list) -- concatenation, and show to convert the integers into strings main = do input <- readFile "inputfile" let ilines = lines input let iRecords = map parseLine iLines let oRecords = sort iRecords -- comparison on tuples is automatically defined if all element types -- are comparable (typeclass Ord) let olines = map showRecord oRecords let output = unlines olines putStr output -- or writeFile "outputfile" output
I have defined functions to perform an insertion sort given a tuple of the above specification.
Why not import List(sort) or import List(sortBy), if you need your own comparison?
Thanks for your time in explaining this to me
Graeme Turner
Regards, Hannah.