add scripting integration for haskell

[subes]

https://eta-lang.org/

Unsuitable because there is no ScriptEngine in eta: typelead/eta#466

[subes]

Better alternative: https://github.com/Frege/frege-interpreter

Call Java from Frege:
http://mmhelloworld.github.io/blog/2013/07/10/frege-hello-java/

blocker: Frege/frege-interpreter#36 (comment) (fixed)

Repl with:
java -cp frege3.25-latest.jar frege.repl.FregeRepl

https://learnyouahaskell.com/introduction
https://github.com/Frege/frege/wiki/LYAH-adaptions-for-Frege
https://dierk.gitbooks.io/fregegoodness/content/

Frege ScriptEngine has a few flaws:

• println does not work
• arbitrary issues with multiple statements in a script (which works fine in repl)
• can not find a way to access bindings

[subes]

Won't do since ScriptEngines don't work for In-JVM usage. Could introduce a REPL based binding (which should also work for vanilla haskell "ghci"), but this would be in a separate project, not in invesdwin-context.

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GHCI interpreter: https://stackoverflow.com/a/2144410

arch install "cabal-install" and "ghc-static"

cabal update
cabal install hint

$ ghci

import Language.Haskell.Interpreter
runInterpreter $ setImports ["Prelude"] >> eval "3 + 5"

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hGetLine to read a line from a socket: https://stackoverflow.com/questions/25040884/hgetcontents-vs-hgetline

hPutStrLn to write to socket
https://stackoverflow.com/questions/37143458/socket-programming-in-haskell-putstrln-hputstrln-not-behaving-as-expected

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we need to use file communication

• since haskell does not easily support global state to store a socket connection => instead directly replacing file references in function
• since frege does not support sockets, instead one would have to implement one as a module manually which does not work inside the repl without a module file => instead defining a callback function with file handling embedded

Frege file reading:
https://stackoverflow.com/questions/19086049/what-is-the-frege-equivalent-to-haskell-readfile
https://github.com/Frege/frege/blob/master/frege/java/IO.fr#L190
frege also has writeFile/readFile https://github.com/Frege/frege/blob/a6787bc102536e03f7dc805a517b1741f13b5739/frege/Prelude.fr#L151

Haskell file reading:
https://stackoverflow.com/questions/28533626/reading-in-text-file
lines/unlines to add/remove newlines https://stackoverflow.com/questions/52290934/haskell-writefile

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handling read errors and retrying after a sleep:

https://scrapingant.com/blog/web-scraping-haskell#handling-errors-and-rate-limiting

frege interpreter: Frege/frege-repl#56

https://github.com/Frege/frege-interpreter/blob/f14bdbe79c13341f4a3e023acfb4f8b15c1fc885/frege-interpreter-core/src/main/frege/frege/scriptengine/FregeScriptEngine.fr#L3