Re: [Haskell-cafe] Data.List / Map: simple serialization?

On Friday 10 June 2011, 13:49:23, Dmitri O.Kondratiev wrote:

On Thu, Jun 9, 2011 at 11:31 AM, Max Bolingbroke

...

wrote:

If you want plain text serialization, "writeFile "output.txt" . show" and "fmap read (readFile "output.txt")" should suffice...

Max

This code works:

main = do let xss = [[1,2,3],[4,5,6],[7,8],[9]] writeFile "output.txt" (show xss) line <- readFile "output.txt" let xss2 = read line :: [[Int]] print xss2

As soon as complete file is returned as a single line, using 'fmap' does not make sense here: line <- readFile "output.txt" let xss2 = fmap read line

When to use 'fmap'?

xss2 <- fmap read (readFile "output.txt") or xss2 <- read `fmap` readFile "output.txt" But it might be necessary to tell the compiler which type xss2 ought to have, so it knows which `read' to invoke, if it can't infer that from later use.