Eval plugin: evaluate expressions as statements

[berberman]

Closes #1577

#438 introduced an alternative way to evaluate expressions: we wrapped expressions with asPrint, and then used compileExpr to get the coerced result IO String. However, it broke functionality of it variable -- referencing the last evaluated result.

This PR restores the old eval plugin's behaviour: there is no special treatment for expressions anymore; instead, expressions are just statements, and we redirect the output of execStmt to a temporary file to get the same result as compileExpr.

[pepeiborra]

Very nice!

[berberman]

All test cases on Windows are failing:

lexical error in string/character literal at character 'U'

Perhaps an encoding-related issue?

[jneira]

@berberman mmm, i think you will have to save the file using utf-8, not sure how being in a evaluated expression, see

haskell-language-server/plugins/hls-hlint-plugin/src/Ide/Plugin/Hlint.hs

Lines 399 to 403 in b9c6e6c

	let writeFileUTF8NoNewLineTranslation file txt =
	withFile file WriteMode $ \h -> do
	hSetEncoding h utf8
	hSetNewlineMode h noNewlineTranslation
	hPutStr h (T.unpack txt)

(maybe you will not need the newline thing)

There is a function in the extra package writeUtf8 but i guess maybe you cant use it in that context.

[berberman]

Never mind, I found it might be caused by the backslash was not escaped properly