Lambda-lifting

[j-hui]

We need to convert lambdas (aka closures) into top-level function definitions. So this:

f = \x -> (\() -> x) ()

should be converted to

type Fenv a = Fenv { x : a }

f__anon1 = \fenv -> \() -> fenv.x

f = \x -> f__anon (Fenv a) ()

That is, any lambdas that don't appear at the top-level of a top-level function definition should be hoisted into a name-mangled top-level definition and given an extra "environment" parameter that includes all variables captured by closure.