DSL compiler for simple While language

[ailrst]

This PR adds functions to the DSL so that code can be written in a simple while language and compiled to BASIL IR basic blocks, this adds:

If (cond) Then (... blocks ...) Else (... blocks ...)

While (cond) Do (... blocks ...)

For (init, cond, incr) Do (... blocks ...)

It also adds infix operators to build basil IR expressions.

val p = prog(
  proc(
    "is_prime",
    Seq("n" -> bv64),
    Seq("ans" -> bv1),
    blocks(
      If(n <= 1.bv64)
        Then (ret("ans" -> (0.bv1)))
        Else (For(i := (2.bv64), i < n, i := i + (1.bv64))
          Do (If(n % i === (0.bv64)) Then (ret("ans" -> (0.bv1))))),
      ret("ans" -> (1.bv1))
    )
  )
)

[katrinafyi]

Big changes!

Really fast preliminary comments:

• I think the new higher DSL should be in a separate file.
• also, it would be nice to organise the internal case classes separately from the user-facing functions as much as possible. for example, maybe they can be inside an object and marked private.
• are there guards against "invalid syntax". like putting two else clauses on a single if statement?

[ailrst]

Reviewing this can wait until you're at work of course but, I agree with the above.

are there guards against "invalid syntax". like putting two else clauses on a single if statement?

Yes, though in many places the errors can be quite confusing if you don't know the implementation (esp. due to overloading, using implicit conversions seems to work better). For this case it should be fairly reasonable, If is a case class that only defines the method Then which returns a new case class which only defines the method Else, so you'll get a not found error if you write something else.