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feat(compiler): wrap partial application in anonymous functions #92

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feat(compiler): wrap partial application in anonymous functions #92

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2238b38
feat(compiler): wrap partial application in anonymous functions
michallepicki Mar 30, 2021
d7a121f
fix test
michallepicki Mar 30, 2021
e584bf4
add failing test for broken specs
michallepicki Mar 30, 2021
568c0e4
remove empty file
michallepicki Mar 30, 2021
cc25661
remove incorrect test, use shorter generated variable names
michallepicki Apr 1, 2021
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18 changes: 17 additions & 1 deletion caramel/compiler/ocaml_to_erlang/fun.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -245,6 +245,8 @@ and mk_expression exp ~var_names ~modules ~functions ~module_name =
in
Erlang.Ast.Expr_tuple [ tag; value ]
| Texp_apply (expr, args) ->
let expr_arg_types, _ = Uncurry.uncurry_tarrow expr.exp_type [] in
let wanted_arity = List.length expr_arg_types in
let name =
match
mk_expression expr ~var_names ~modules ~functions ~module_name
Expand All @@ -261,7 +263,21 @@ and mk_expression exp ~var_names ~modules ~functions ~module_name =
(mk_expression arg ~var_names ~modules ~functions ~module_name))
args
in
Expr.apply name args
if wanted_arity > List.length args then
let rec gen_names acc n =
match n with
| 0 -> acc
| n ->
gen_names
(Name.var ("Caramel@" ^ string_of_int n) :: acc)
(n - 1)
in
let outer_names = gen_names [] (wanted_arity - List.length args) in
let lhs = List.map Pat.bind outer_names in
let idents = List.map Expr.ident outer_names in
let rhs = Expr.apply name (args @ idents) in
Expr.fun_ ~cases:[ FunDecl.case ~lhs ~guard:None ~rhs ]
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If I understand this correctly, you're

  1. computed the arity of this particular function type, using Uncurry.uncurry_tarrow/2
  2. checking if we're applying this function with the as many arguments as the arity indicated by the type from 1)
  3. if we are missing arguments, create a function that will take the missing arguments and pass them on to the function from 1)

I think this will break for named and default arguments, so we need to have another look at this.

This can be problematic because fun's in Erlang can have a single arity, but multiple clauses. This means that a function f ?(x = 1) y = x + y would translate to 2 erlang functions:

f(Y) -> f(1, Y).
f(X, Y) -> X + Y.

And a function with named arguments like f ~x ~y = x / y would need to be kept track until is fully applied before we can call it.

For example, what does let div_one = (f ~y: 1) translate to?

Div_one = fun (X) -> f(1, X) end,

% or
Div_one = fun (X) -> f(X, 1) end,

I think we may need to take a step back and rethink this. It's turning out to be a tad more complex than I thought id' be at first 😅

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this will break for named and default arguments,

which are not supported right now anyway, but I understand we should think ahead...

Gleam supports labeled arguments, and I think those are probably fine to figure out at Caramel compilation time. Not sure about default arguments, they indeed seem tricky. What values are allowed? Just simple literals? If so then maybe they are just in the typedtree and could be fetched from there and printed when needed...

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This means that a function f ?(x = 1) y = x + y would translate to 2 erlang functions:

I would propose only generate the full arguments version in the resulting Erlang, so only support optional / labeled arguments when called in from Caramel, not other langs.

For example, what does let div_one = (f ~y:1) translate to?

This depends on the way f was declared, because of the order, and the rules of Ocaml erasure would need to be preserved. So assuming it is f x ~y = x + y which in erlang is just f(X, Y), then

Div_one = fun (X) -> f(X, 1) end,

and if f ~y x = x + y then fun (X) -> f(1, X) end,

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Or even generate the erlang functions with smaller arity for optional arguments, but only for erlang/elixir interoperability (don't use them from caramel because it's unnecessarily complicating things), and only if there is just one optional or have some rules like Elixir that they can be ommited inclusively starting from the end only.

In any case I think we can figure it out and if not, caramel is not 1.0 anyway :)

else Expr.apply name args
| Texp_record { fields; extended_expression; _ } -> (
let fields =
fields |> Array.to_list
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6 changes: 6 additions & 0 deletions tests/compiler/expressions.t/apply.ml
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Expand Up @@ -32,3 +32,9 @@ let lambda () =
let _ = f () in
let _ = f' 1 in
f'' 1 2

let abs_diff_times x y z = (Erlang.abs (x - y)) * z

let partial_application () =
let f = abs_diff_times 3 in
f (-1) 2
12 changes: 12 additions & 0 deletions tests/compiler/expressions.t/run.t
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Expand Up @@ -33,12 +33,14 @@
% Source code generated with Caramel.
-module(apply).

-export([abs_diff_times/3]).
-export([f/1]).
-export([f1/1]).
-export([f2/2]).
-export([f3/3]).
-export([f4/4]).
-export([lambda/0]).
-export([partial_application/0]).
-export([run/0]).

-spec f(_) -> _.
Expand Down Expand Up @@ -79,6 +81,16 @@
F_prime(1),
F_prime_prime(1, 2).

-spec abs_diff_times(integer(), integer(), integer()) -> integer().
abs_diff_times(X, Y, Z) -> erlang:'*'(erlang:abs(erlang:'-'(X, Y)), Z).

-spec partial_application() -> integer().
partial_application() ->
F = fun
(Caramel@1, Caramel@2) -> abs_diff_times(3, Caramel@1, Caramel@2)
end,
F(-1, 2).


$ caramel compile binding_on_match.ml
File "binding_on_match.ml", line 4, characters 57-68:
Expand Down