Function parameter type hints

[zjhmale]

https://code.visualstudio.com/docs/extensionAPI/vscode-api#SignatureHelpProvider

Since Haskell-like syntax does not have parenthesis and commas for functions, things may get tricky here. If use some backtracking to find the nearest function definition, a big overhead of trying to get type information of each identifier in the backtracking path stands there. This feature seems to be impossible to be implemented at present. On a second thought, if we can backtracking to find the nearest function and to match the number of arguments can still finish the job.

And the case to support signature hint for function call inside parenthesis e.g. (fun arg...) is much more straightforward.

- [ ] signature hint for open function calls There is partial evaluation stands there, e.g., map ƒ ... so it will be crazy complicate and hard to give a 100% promise of precise, support for close functions is best we can do here for parameter type hints.

• signature hint for close function calls