3 new lexer examples

[PiotrJustyna]

First of all, thank you for your fantastic work on alex. I keep coming back to this repository.

I recently found myself needing more information from lexing errors, specifically error position in the input. I've been using the basic wrapper, then switched to posn and finally landed on monad. I had a difficult time putting together the full picture of an alex file implementing the monad wrapper and once I finally got it done, I thought my files could help somebody.

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Additionally, I made two small improvements/fixes so the examples compile with ghc 9.8.4:

• import Data.Char (ord) required by examples:
  • haskell.x
  • tiger.x
• I changed alex location to where my cabal places it. Probably not the most portable thing and something better could be used but it does work and gives the user an idea of where to look for alex: ALEX=../dist-newstyle/build/x86_64-linux/ghc-9.8.4/alex-3.5.4.0/x/alex/build/alex/alex

[andreasabel]

Thanks for the contribution!

I tried make ALEX=alex all in the examples directory but it does not build (nor run) your new examples.

One simple fix would be to move your examples out of wyvern/ and prefix these files with wyvern- instead.

[andreasabel]

This does not seem very portable nor future proof.
The old setting isn't great either, but at least it works with cabal v1-build independent of the GHC version and OS.
Maybe it is best to port the logic from /tests/Makefile.

[PiotrJustyna]

Thank you for reviewing @andreasabel. I applied your feedback and managed to avoid rearranging wyvern files so they are still nicely compartmentalized. Please let me know if you think there's something missing.

[andreasabel]

Thanks!

I can run these examples now as described in the readme, once I built them with cabal exec -- make.