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zthzth
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PoC of let.unwrap
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‎compiler/frontend/ast_attributes.ml‎

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Original file line numberDiff line numberDiff line change
@@ -199,6 +199,12 @@ let has_bs_optional (attrs : t) : bool =
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true
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| _ -> false)
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let has_unwrap_attr (attrs : t) : bool =
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Ext_list.exists attrs (fun ({txt}, _) ->
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match txt with
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| "let.unwrap" -> true
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| _ -> false)
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let iter_process_bs_int_as (attrs : t) =
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let st = ref None in
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Ext_list.iter attrs (fun (({txt; loc}, payload) as attr) ->

‎compiler/frontend/ast_attributes.mli‎

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Original file line numberDiff line numberDiff line change
@@ -46,6 +46,8 @@ val iter_process_bs_string_as : t -> string option
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val has_bs_optional : t -> bool
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val has_unwrap_attr : t -> bool
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val iter_process_bs_int_as : t -> int option
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type as_const_payload = Int of int | Str of string * External_arg_spec.delim

‎compiler/frontend/bs_builtin_ppx.ml‎

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Original file line numberDiff line numberDiff line change
@@ -143,6 +143,75 @@ let expr_mapper ~async_context ~in_function_def (self : mapper)
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] ) ->
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default_expr_mapper self
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{e with pexp_desc = Pexp_ifthenelse (b, t_exp, Some f_exp)}
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(* Transform:
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- `@let.unwrap let Ok(inner_pat) = expr`
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- `@let.unwrap let Some(inner_pat) = expr`
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...into switches *)
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| Pexp_let
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( Nonrecursive,
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[
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{
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pvb_pat =
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{
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ppat_desc =
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Ppat_construct
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( {txt = Lident (("Ok" | "Some") as variant_name)},
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Some _inner_pat );
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} as pvb_pat;
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pvb_expr;
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pvb_attributes;
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};
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],
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body )
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when Ast_attributes.has_unwrap_attr pvb_attributes -> (
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let variant =
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match variant_name with
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| "Ok" -> `Result
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| _ -> `Option
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in
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match pvb_expr.pexp_desc with
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| Pexp_pack _ -> default_expr_mapper self e
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| _ ->
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let ok_case =
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{
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Parsetree.pc_bar = None;
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pc_lhs = pvb_pat;
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pc_guard = None;
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pc_rhs = body;
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}
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in
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let loc = Location.none in
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let error_case =
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match variant with
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| `Result ->
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{
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Parsetree.pc_bar = None;
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pc_lhs =
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Ast_helper.Pat.construct ~loc
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{txt = Lident "Error"; loc}
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(Some (Ast_helper.Pat.var ~loc {txt = "e"; loc}));
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pc_guard = None;
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pc_rhs =
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Ast_helper.Exp.construct ~loc
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{txt = Lident "Error"; loc}
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(Some (Ast_helper.Exp.ident ~loc {txt = Lident "e"; loc}));
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}
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| `Option ->
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{
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Parsetree.pc_bar = None;
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pc_lhs =
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Ast_helper.Pat.construct ~loc {txt = Lident "None"; loc} None;
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pc_guard = None;
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pc_rhs =
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Ast_helper.Exp.construct ~loc {txt = Lident "None"; loc} None;
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}
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in
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default_expr_mapper self
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{
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e with
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pexp_desc = Pexp_match (pvb_expr, [ok_case; error_case]);
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pexp_attributes = e.pexp_attributes @ pvb_attributes;
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})
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| Pexp_let
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( Nonrecursive,
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[

‎tests/tests/src/LetUnwrap.mjs‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,161 @@
1+
// Generated by ReScript, PLEASE EDIT WITH CARE
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function doStuffWithResult(s) {
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if (s === "s") {
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return {
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TAG: "Ok",
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_0: "hello"
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};
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} else {
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return {
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TAG: "Error",
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_0: "InvalidString"
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};
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}
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}
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function doNextStuffWithResult(s) {
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if (s === "s") {
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return {
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TAG: "Ok",
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_0: "hello"
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};
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} else {
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return {
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TAG: "Error",
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_0: "InvalidNext"
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};
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}
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}
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function getXWithResult(s) {
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let y = doStuffWithResult(s);
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if (y.TAG !== "Ok") {
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return {
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TAG: "Error",
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_0: y._0
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};
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}
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let y$1 = y._0;
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let x = doNextStuffWithResult(y$1);
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if (x.TAG === "Ok") {
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return {
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TAG: "Ok",
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_0: x._0 + y$1
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};
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} else {
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return {
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TAG: "Error",
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_0: x._0
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};
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}
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}
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let x = getXWithResult("s");
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let someResult;
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someResult = x.TAG === "Ok" ? x._0 : (
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x._0 === "InvalidNext" ? "nope!" : "nope"
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);
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function doStuffWithOption(s) {
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if (s === "s") {
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return "hello";
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}
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}
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function doNextStuffWithOption(s) {
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if (s === "s") {
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return "hello";
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}
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}
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function getXWithOption(s) {
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let y = doStuffWithOption(s);
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if (y === undefined) {
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return;
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}
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let x = doNextStuffWithOption(y);
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if (x !== undefined) {
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return x + y;
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}
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}
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let x$1 = getXWithOption("s");
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let someOption = x$1 !== undefined ? x$1 : "nope";
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async function doStuffResultAsync(s) {
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if (s === "s") {
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return {
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TAG: "Ok",
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_0: {
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s: "hello"
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}
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};
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} else {
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return {
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TAG: "Error",
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_0: "FetchError"
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};
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}
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}
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async function decodeResAsync(res) {
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let match = res.s;
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if (match === "s") {
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return {
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TAG: "Ok",
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_0: res.s
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};
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} else {
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return {
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TAG: "Error",
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_0: "DecodeError"
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};
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}
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}
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async function getXWithResultAsync(s) {
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let res = await doStuffResultAsync(s);
126+
if (res.TAG !== "Ok") {
127+
return {
128+
TAG: "Error",
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_0: res._0
130+
};
131+
}
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let res$1 = res._0;
133+
console.log(res$1.s);
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let x = await decodeResAsync(res$1);
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if (x.TAG === "Ok") {
136+
return {
137+
TAG: "Ok",
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_0: x._0
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};
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} else {
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return {
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TAG: "Error",
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_0: x._0
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};
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}
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}
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export {
149+
doStuffWithResult,
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doNextStuffWithResult,
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getXWithResult,
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someResult,
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doStuffWithOption,
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doNextStuffWithOption,
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getXWithOption,
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someOption,
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doStuffResultAsync,
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decodeResAsync,
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getXWithResultAsync,
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}
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/* x Not a pure module */

‎tests/tests/src/LetUnwrap.res‎

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,69 @@
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let doStuffWithResult = s =>
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switch s {
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| "s" => Ok("hello")
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| _ => Error(#InvalidString)
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}
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7+
let doNextStuffWithResult = s =>
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switch s {
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| "s" => Ok("hello")
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| _ => Error(#InvalidNext)
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}
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let getXWithResult = s => {
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@let.unwrap let Ok(y) = doStuffWithResult(s)
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@let.unwrap let Ok(x) = doNextStuffWithResult(y)
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Ok(x ++ y)
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}
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let someResult = switch getXWithResult("s") {
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| Ok(x) => x
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| Error(#InvalidString) => "nope"
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| Error(#InvalidNext) => "nope!"
23+
}
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25+
let doStuffWithOption = s =>
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switch s {
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| "s" => Some("hello")
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| _ => None
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}
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let doNextStuffWithOption = s =>
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switch s {
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| "s" => Some("hello")
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| _ => None
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}
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let getXWithOption = s => {
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@let.unwrap let Some(y) = doStuffWithOption(s)
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@let.unwrap let Some(x) = doNextStuffWithOption(y)
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Some(x ++ y)
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}
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let someOption = switch getXWithOption("s") {
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| Some(x) => x
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| None => "nope"
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}
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type res = {s: string}
49+
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let doStuffResultAsync = async s => {
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switch s {
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| "s" => Ok({s: "hello"})
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| _ => Error(#FetchError)
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}
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}
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57+
let decodeResAsync = async res => {
58+
switch res.s {
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| "s" => Ok(res.s)
60+
| _ => Error(#DecodeError)
61+
}
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}
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64+
let getXWithResultAsync = async s => {
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@let.unwrap let Ok({s} as res) = await doStuffResultAsync(s)
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Console.log(s)
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@let.unwrap let Ok(x) = await decodeResAsync(res)
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Ok(x)
69+
}

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