closures.md

OCaml Closures

For an overview of the OCaml closure memory representation, see this excellent summary by Gbury.

Inserting dups/drops for closures

Uncurried closures

Suppose the free variables captured by the closure are y0, y1, ..., ym.

Then,

let closure a0 a1 ... an env = <closure body>

transforms to

let closure a0 a1 ... an env =
    (* Dup the environment *)
    let x0 = dup (field 0 (offset env)) in
    let x1 = dup (field 1 (offset env)) in 
    ...
    let xm = dup (field m (offset env)) in
    (* Drop the closure *)
    drop env ;
    (* Execute the closure *)
    <closure body>[x0/y0][x1/y1]...[xm/ym]

where

• env : closure_block_addr is the field implicitly passed by the OCaml compiler that points to the start of the closure block in memory
• offset : closure_block_addr -> env_addr returns the address of the start of the closure environment given the start of the closure block.

Curried closures

TODO