SAWScript REPL doesn't have help for syntactic constructs

[sauclovian-g]

It would be nice if this in particular worked:

sawscript> :help import

but I think in general there should be a help text for all reserved words.

It isn't entirely obvious how best to extend the help system to handle these.

[samcowger]

The core logic of :help is pretty much just map lookup:

saw-script/saw-script/src/SAWScript/REPL/Command.hs

Lines 353 to 365 in 0c79042

	helpCmd :: String -> REPL ()
	helpCmd cmd
	| null cmd = io (mapM_ putStrLn (genHelp commandList))
	| otherwise =
	do env <- getEnvironment
	case Map.lookup (Text.pack cmd) (rwDocs env) of
	Just d -> io $ putStr d
	-- FIXME? can we restore the ability to lookup doc strings from Cryptol?
	-- | Just (ec,_) <- lookup cmd builtIns =
	-- io $ print $ helpDoc ec
	Nothing -> do io $ putStrLn $ "// No documentation is available."
	typeOfCmd cmd

I imagine it's quite feasible to add stuff to rwDocs to make it available for lookup here. Perhaps we could use an actual enum, rather than Text, to represent reserved words in SAWScript.Token.Token's TReserved, and write out help text for each variant?

[sauclovian-g]

rwDocs isn't the right place to keep it; that's specifically the value namespace. It should probably check for colon commands first, then reserved words, then look in the value namespace, then the type namespace. Or maybe it should check all the namespaces and print all the help entries it finds. It shouldn't be possible to have identifiers that overlap with reserved words, but it's definitely possible to have values and types with the same names.

Right now there's no help text for types or colon commands either (that's #2583 and #2582 respectively) and a prerequisite for #253 (add a SAWScript prelude) is adding declaration syntax for help text. (None of that needs to be done all at once necessarily, just providing context because it shapes the solution choices)