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Update GHCi users guide documentation

hdgarrood requested to merge hdgarrood/ghc:update-ghci-docs into master

I noticed that when I was looking through the users guide for the 9.4.1 alpha-1 release, the GHCi guide makes use of the fact that GHCi uses timestamps for recompilation checking by touch-ing a file in order to trigger recompilation. Of course, since !5661 (merged), this no longer works - the compiler compares the MD5 hash of the source file to the hash from the last time it compiled that module, and of course it is unchanged. I went in to update this to use echo to append a comment to the end of the file in order to ensure that a recompilation is triggered, and in the process I realised that there are a few other ways that the current behaviour of GHCi differs from what is described here, so I have updated these too. All of the output lines I've modified are from a session with GHC 9.4.1-alpha1.

The main difference (aside from the touch change) is that it appears that at some point, GHC became more strict about compiling modules to static vs dynamic object code. It appears that at some point GHC might have inferred -dynamic based on the object files that already exist, so that you were only required to specify -dynamic in the first invocation to compile D.hs, whereas now if you try to compile separate modules with different static/dynamic settings you get an error:

$ ghc -c -dynamic D.hs
$ ghc -c C.hs

C.hs:3:1: error:
    Bad interface file: ./D.hi
        mismatched interface file profile tag (wanted "", got "dyn")
3 | import D
  | ^^^^^^^^

So it seemed to me that the most sensible way to update this guide was to specify -dynamic in each ghc invocation.

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