Tool for formatting / inferring types

[Pauan]

Some other languages (like go and Rust) have a tool which you can use to automatically format source code according to style guidelines.

In addition to formatting code, it would also be useful if the tool could infer Koka types and insert type annotations into the code.

As an example, let's say you had this Koka code:

fun foo(a) {
  a + 5
}

After running the format tool, it would replace the code with this:

fun foo(a: int): int {
  a + 5
}

If the inferred type is ambiguous, the tool can ask the programmer to choose from a list of possible types.

This gives the convenience of type inference (not needing to write out the types), but also gives the benefits of explicit type signatures (more robust, better documentation, faster compiling, and easier to read)

[anfelor]

This seems like a good proposal for the language server at #100 :)
Koka now has a --showtypesigs option that prints all top-level type signatures into the console