[Haskell-cafe] Source code location in IO?

[Augustsson, Lennart]

It's totally compatible with Haskell semantics, since Haskell does not give any semantics to IO.
Anything can happen when you do IO.  But it's still a bit weird. :)

-----Original Message-----
From: Haskell-Cafe [mailto:haskell-cafe-bounces at haskell.org] On Behalf Of Tom Ellis
Sent: 20 June 2016 16:04
To: haskell-cafe at haskell.org
Subject: [Haskell-cafe] Source code location in IO?

Is it compatible with the semantics of Haskell to have a function

    sourceLocation :: IO String

which when run returns the source file location at which it is used?  For example, suppose Main.hs is

    module Main where
    
    main = do
       putStrLn =<< sourceLocation
       putStrLn "Hello"
       putStrLn =<< sourceLocation

It would print the following when run

    Main.hs:4
    Hello
    Main.hs:6

and

    module Main where
    
    main = do
       let s = sourceLocation
       putStrLn =<< s
       putStrLn "Hello"
       putStrLn =<< s

It would print the following when run

    Main.hs:4
    Hello
    Main.hs:4

If this is not compatible with the semantics of Haskell, why not?  I agree that the two programs must have the same denotation, but is there anything that requires them to have the same output when run?

Tom

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