wasm/closure — captured locals in WASM

Closures work in the WASM backend, including capturing locals from the enclosing scope. The runtime allocates a closure object on the WASM linear memory; the GC reclaims it when unreferenced.

Source (examples/wasm/closure.rail):

apply f x = f x

main =
  let scale = 10
  let mul = \x -> x * scale
  let _ = print (show (apply mul 7))
  let offset = 100
  let add = \x -> x + offset
  let _ = print (show (apply add 42))
  0

Build:

./rail_native wasm examples/wasm/closure.rail

Output:

Compiling examples/wasm/closure.rail to WASM...
  WAT: 53555 bytes
  wat2wasm: OK
  Binary: /tmp/rail_out.wasm

When loaded in a WASM host, this prints 70 (7 * 10) and 142 (42 + 100). The two closures each capture their respective local (scale, offset) at allocation time.