mpri-funcprog-project/src/Top.ml

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2017-12-13 14:04:28 +01:00
(* This intermediate language describes the result of defunctionalization.
It retains the key features of the previous calculus, [Tail], in that
the ordering of computations is explicit and every function call is a
tail call. Furthermore, lambda-abstractions disappear. A memory block
[Con] now contains an integer tag followed with a number of fields,
which hold values. A [switch] construct appears, which allows testing
the tag of a memory block. A number of (closed, mutually recursive)
functions can be defined at the top level. *)
type tag =
int
and variable =
Atom.atom
and binop = Tail.binop =
| OpAdd
| OpSub
| OpMul
| OpDiv
and value = Tail.value =
| VVar of variable
| VLit of int
| VBinOp of value * binop * value
(* A block contains an integer tag, followed with a number of fields. *)
and block =
| Con of tag * value list
(* The construct [Swi (v, branches)] reads the integer tag stored in the
memory block at address [v] and performs a case analysis on this tag,
transferring control to the appropriate branch. (The value [v] should be a
pointer to a memory block.) *)
and term =
| Exit
| TailCall of variable * value list
| Print of value * term
| LetVal of variable * value * term
| LetBlo of variable * block * term
| IfZero of value * term * term
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| Swi of value * branch list
(* A branch [tag xs -> t] is labeled with an integer tag [tag], and is
executed if the memory block carries this tag. The variables [xs] are
then bounds to the fields of the memory block. (The length of the list
[xs] should be the number of fields of the memory block.) *)
and branch =
| Branch of tag * variable list * term
(* A toplevel function declaration mentions the function's name, formal
parameters, and body. *)
and function_declaration =
| Fun of variable * variable list * term
(* A complete program consits of a set of toplevel function declarations
and a term (the "main program"). The functions are considered mutually
recursive: every function may refer to every function. *)
and program =
| Prog of function_declaration list * term
[@@deriving show { with_path = false }]
(* -------------------------------------------------------------------------- *)
(* Constructor functions. *)
let vvar =
Tail.vvar
let vvars =
Tail.vvars
(* [let x_1 = v_1 in ... let x_n = v_n in t] *)
let rec sequential_let (xs : variable list) (vs : value list) (t : term) =
match xs, vs with
| [], [] ->
t
| x :: xs, v :: vs ->
LetVal (x, v, sequential_let xs vs t)
| _ ->
assert false
(* [let x_1 = v_1 and ... x_n = v_n in t] *)
let parallel_let (xs : variable list) (vs : value list) (t : term) =
assert (List.length xs = List.length vs);
assert (Atom.Set.disjoint (Atom.Set.of_list xs) (Tail.fv_values vs));
sequential_let xs vs t