comments and changelog

Author: zth

CHANGELOG.md

@@ -20,7 +20,8 @@
 
 - Use FORCE_COLOR environmental variable to force colorized output https://github.com/rescript-lang/rescript-compiler/pull/7033
 - Allow spreads of variants in patterns (`| ...someVariant as v => `) when the variant spread is a subtype of the variant matched on. https://github.com/rescript-lang/rescript-compiler/pull/6721
-- Fix the issue where dynamic imports are not working for function-defined externals. https://github.com/rescript-lang/rescript-compiler/pull/7060 
+- Fix the issue where dynamic imports are not working for function-defined externals. https://github.com/rescript-lang/rescript-compiler/pull/7060
+- Allow pattern matching on dicts. `switch someDict { | dict{"one": 1} => Js.log("one is one") }` https://github.com/rescript-lang/rescript-compiler/pull/7059
 
 #### :bug: Bug fix
 
@@ -316,7 +317,7 @@
 
 #### :rocket: New Feature
 
-- Experimental support of tagged template literals, e.g. ```sql`select * from ${table}```. https://github.com/rescript-lang/rescript-compiler/pull/6250
+- Experimental support of tagged template literals, e.g. `` sql`select * from ${table} ``. https://github.com/rescript-lang/rescript-compiler/pull/6250
 - Experimental support for generic/custom JSX transforms. https://github.com/rescript-lang/rescript-compiler/pull/6565
 - `dict` is now a builtin type. https://github.com/rescript-lang/rescript-compiler/pull/6590
 
@@ -496,7 +497,7 @@ No changes compared to rc.9.
 
 #### :boom: Breaking Change
 
-- Stop mangling object field names. If you had objects with field names containing "__" or leading "_", they won't be mangled in the compiled JavaScript and represented as it is without changes. https://github.com/rescript-lang/rescript-compiler/pull/6354
+- Stop mangling object field names. If you had objects with field names containing "\__" or leading "_", they won't be mangled in the compiled JavaScript and represented as it is without changes. https://github.com/rescript-lang/rescript-compiler/pull/6354
 
 #### :bug: Bug Fix
 
@@ -551,7 +552,7 @@ No changes compared to rc.9.
 
 #### :rocket: New Feature
 
-- Introduced a new  `%ffi` extension (*experimental* - not for production use!) that provides a more robust mechanism for JavaScript function interoperation by considering function arity in type constraints. This enhancement improves safety when dealing with JavaScript functions by enforcing type constraints based on the arity of the function. https://github.com/rescript-lang/rescript-compiler/pull/6251
+- Introduced a new `%ffi` extension (_experimental_ - not for production use!) that provides a more robust mechanism for JavaScript function interoperation by considering function arity in type constraints. This enhancement improves safety when dealing with JavaScript functions by enforcing type constraints based on the arity of the function. https://github.com/rescript-lang/rescript-compiler/pull/6251
 - Extended untagged variants with function types. https://github.com/rescript-lang/rescript-compiler/pull/6279
 
 #### :boom: Breaking Change
@@ -629,14 +630,14 @@ No changes compared to rc.9.
 
 #### :bug: Bug Fix
 
-- Fix broken formatting in uncurried mode for functions with _ placeholder args. https://github.com/rescript-lang/rescript-compiler/pull/6148
+- Fix broken formatting in uncurried mode for functions with \_ placeholder args. https://github.com/rescript-lang/rescript-compiler/pull/6148
 - Fix issue where spreading record types with optional labels would not have their labels preserved as optional. https://github.com/rescript-lang/rescript-compiler/pull/6154
 - Fix error location to be the type with the spreads when spreading record types with duplicate labels. https://github.com/rescript-lang/rescript-compiler/pull/6157
 - Disable warning on `@inline` attibute on uncurried functions. https://github.com/rescript-lang/rescript-compiler/pull/6152
 - Support doc comments on arguments of function types. https://github.com/rescript-lang/rescript-compiler/pull/6161
 - Fix issue with record type coercion and unboxed. https://github.com/rescript-lang/rescript-compiler/issues/6158
 - Fixed subtype checking for record types with "@as" attributes: The subtype relationship now takes into account the compatibility of "@as" attributes between corresponding fields, ensuring correctness in runtime representation.
- https://github.com/rescript-lang/rescript-compiler/issues/6158
+  https://github.com/rescript-lang/rescript-compiler/issues/6158
 - Emit directive above header comment. https://github.com/rescript-lang/rescript-compiler/pull/6172
 - Add error message to private extension. https://github.com/rescript-lang/rescript-compiler/pull/6175
 
@@ -665,7 +666,6 @@ No changes compared to rc.9.
 
 - Special case generation of uncurried functions with 1 argument of unit type so they don't take a parameter. https://github.com/rescript-lang/rescript-compiler/pull/6131
 
-
 # 11.0.0-alpha.1
 
 #### :rocket: Main New Feature
@@ -676,16 +676,16 @@ No changes compared to rc.9.
 #### :rocket: New Feature
 
 - Add support for uncurried mode: a mode where everything is considered uncurried, whether with or without the `.`. This can be turned on with `@@uncurried` locally in a file. For project-level configuration in `bsconfig.json`, there's a boolean config `"uncurried"`, which propagates to dependencies, to turn on uncurried mode.
-Since there's no syntax for partial application in this new mode, introduce `@res.partial foo(x)` to express partial application. This is temporary and will later have some surface syntax.
-Make uncurried functions a subtype of curried functions, and allow application for uncurried functions.
-The `make` function of components is generated as an uncurried function.
-Use best effort to determine the config when formatting a file.
-https://github.com/rescript-lang/rescript-compiler/pull/5968 https://github.com/rescript-lang/rescript-compiler/pull/6080 https://github.com/rescript-lang/rescript-compiler/pull/6086 https://github.com/rescript-lang/rescript-compiler/pull/6087
+  Since there's no syntax for partial application in this new mode, introduce `@res.partial foo(x)` to express partial application. This is temporary and will later have some surface syntax.
+  Make uncurried functions a subtype of curried functions, and allow application for uncurried functions.
+  The `make` function of components is generated as an uncurried function.
+  Use best effort to determine the config when formatting a file.
+  https://github.com/rescript-lang/rescript-compiler/pull/5968 https://github.com/rescript-lang/rescript-compiler/pull/6080 https://github.com/rescript-lang/rescript-compiler/pull/6086 https://github.com/rescript-lang/rescript-compiler/pull/6087
 - Customization of runtime representation of variants. This is work in progress. E.g. some restrictions on the input. See comments of the form "TODO: put restriction on the variant definitions allowed, to make sure this never happens". https://github.com/rescript-lang/rescript-compiler/pull/6095
 - Introduce untagged variants https://github.com/rescript-lang/rescript-compiler/pull/6103
 - Add support for unary uncurried pipe in uncurried mode https://github.com/rescript-lang/rescript-compiler/pull/5804
 - Add support for partial application of uncurried functions: with uncurried application one can provide a
-subset of the arguments, and return a curried type with the remaining ones https://github.com/rescript-lang/rescript-compiler/pull/5805
+  subset of the arguments, and return a curried type with the remaining ones https://github.com/rescript-lang/rescript-compiler/pull/5805
 - Add support for uncurried externals https://github.com/rescript-lang/rescript-compiler/pull/5815 https://github.com/rescript-lang/rescript-compiler/pull/5819 https://github.com/rescript-lang/rescript-compiler/pull/5830 https://github.com/rescript-lang/rescript-compiler/pull/5894
 - Parser/Printer: unify uncurried functions of arity 0, and of arity 1 taking unit. There's now only arity 1 in the source language. https://github.com/rescript-lang/rescript-compiler/pull/5825
 - Add support for default arguments in uncurried functions https://github.com/rescript-lang/rescript-compiler/pull/5835
@@ -707,12 +707,12 @@ subset of the arguments, and return a curried type with the remaining ones https
   - `rescript convert <reason files>`
 - Remove obsolete built-in project templates and the "rescript init" functionality. This is replaced by [create-rescript-app](https://github.com/rescript-lang/create-rescript-app) which is maintained separately.
 - Do not attempt to build ReScript from source on npm postinstall for platforms without prebuilt binaries anymore.
-- Made pinned dependencies transitive: if *a* is a pinned dependency of *b* and *b* is a pinned dependency of *c*, then *a* is implicitly a pinned dependency of *c*. This change is only breaking if your build process assumes non-transitivity.
+- Made pinned dependencies transitive: if _a_ is a pinned dependency of _b_ and _b_ is a pinned dependency of _c_, then _a_ is implicitly a pinned dependency of _c_. This change is only breaking if your build process assumes non-transitivity.
 - Curried after uncurried is not fused anymore: `(. x) => y => 3` is not equivalent to `(. x, y) => 3` anymore. It's instead equivalent to `(. x) => { y => 3 }`.
-Also, `(. int) => string => bool` is not equivalen to `(. int, string) => bool` anymore.
-These are only breaking changes for unformatted code.
+  Also, `(. int) => string => bool` is not equivalen to `(. int, string) => bool` anymore.
+  These are only breaking changes for unformatted code.
 - Exponentiation operator `**` is now right-associative. `2. ** 3. ** 2.` now compile to `Math.pow(2, Math.pow(3, 2))` and not anymore `Math.pow(Math.pow(2, 3), 2)`. Parentheses can be used to change precedence.
-- Remove unsafe ``` j`$(a)$(b)` ``` interpolation deprecated in compiler version 10 https://github.com/rescript-lang/rescript-compiler/pull/6068
+- Remove unsafe `` j`$(a)$(b)` `` interpolation deprecated in compiler version 10 https://github.com/rescript-lang/rescript-compiler/pull/6068
 - Remove deprecated module `Printexc`
 - `@deriving(jsConverter)` not supported anymore for variant types https://github.com/rescript-lang/rescript-compiler/pull/6088
 - New representation for variants, where the tag is a string instead of a number. https://github.com/rescript-lang/rescript-compiler/pull/6088
@@ -761,19 +761,21 @@ These are only breaking changes for unformatted code.
 # 10.1.4
 
 #### :bug: Bug Fix
+
 - Fix implementation of directives https://github.com/rescript-lang/rescript-compiler/pull/6052
 - Fix issue if the `lib` dir is included in the sources of bsconfig.json https://github.com/rescript-lang/rescript-compiler/pull/6055
 - Fix issue with string escape in pattern match https://github.com/rescript-lang/rescript-compiler/pull/6062
 - Fix issue with literal comparison of string constants https://github.com/rescript-lang/rescript-compiler/pull/6065
 
 #### :rocket: New Feature
+
 - Add support for toplevel `await` https://github.com/rescript-lang/rescript-compiler/pull/6054
 
 #### :nail_care: Polish
 
 - Better error message for extension point https://github.com/rescript-lang/rescript-compiler/pull/6057
 - Improve format check help https://github.com/rescript-lang/rescript-compiler/pull/6056
-- Deprecate unsafe ``` j`$(a)$(b)` ``` interpolation: use string templates ``` `${a}${b}` ``` instead https://github.com/rescript-lang/rescript-compiler/pull/6067
+- Deprecate unsafe `` j`$(a)$(b)` `` interpolation: use string templates `` `${a}${b}` `` instead https://github.com/rescript-lang/rescript-compiler/pull/6067
 
 # 10.1.3
 

jscomp/ml/dict_type_helpers.ml

@@ -1,3 +1,33 @@
+(*
+  An overview of the implementation of dicts in ReScript:
+  ### What is a dict?
+  Dicts are effectively an object with unknown fields, but a single known type of the values it holds.
+
+  ### How are they implemented?
+  Dicts in ReScript are implemented as predefined record type, with a single (magic) field that holds 
+  the type of the dict's values. This field is called `dictValuesType`, and is just an implementation
+  detail - it's never actually exposed to the user, just used internally. 
+
+  The compiler will route any label lookup on the dict record type to the magic field, which creates a 
+  record with unknown keys, but of a single type.
+
+  The reason for this seemingly convoluted implementation is that it allows us to piggyback on the 
+  existing record pattern matching mechanism, which means we get pattern matching on dicts for free.
+
+  ### Modifications to the type checker
+  We've made a few smaller modifications to the type checker to support this implementation:
+
+  - We've added a new predefined type `dict` that is a record with a single field called `dictValuesType`.
+    This type is used to represent the type of the values in a dict.
+  - We've modified the type checker to recognize `dict` patterns, and route them to the predefined `dict` type.
+    This allows us to get full inference for dicts in patterns. 
+    
+  ### Syntax
+  There's first class syntax support for dicts, both as expressions and as patterns.
+  A dict pattern is treated as a record pattern in the compiler and syntax, with an attriubute `@res.dictPattern`
+  attached to it. This attribute is used to tell the compiler that the pattern is a dict pattern, and is what
+  triggers the compiler to treat the dict record type differently to regular record types.
+  *)
 let dict_magic_field_name = "dictValuesType"
 
 let has_dict_pattern_attribute attrs =

jscomp/ml/predef.ml

@@ -220,11 +220,14 @@ let common_initial_env add_type add_extension empty_env =
      type_variance = [Variance.covariant; Variance.covariant]}
   and decl_dict =
     let tvar = newgenvar() in
-    (* Dicts are implented as a as a single "magic" field record. This magic field
-       is then leveraged to be able to piggy back on the existing record pattern
-       matching mechanism. So, this definition is import for the dict pattern
-       matching functionality, but not something intended to be exposed to the
-       user. *) 
+    (* Dicts are implemented as a single "magic" field record. This magic field
+       is the medium through which we can piggy back on the existing record pattern
+       matching mechanism. We do this by letting the compiler route any label lookup
+       for the dict record type to the magic field, which has the type of the values
+       of the dict.
+
+       So, this definition is important for the dict pattern matching functionality, 
+       but not something intended to be exposed to the user. *) 
     {decl_abstr with
       type_attributes = [Dict_type_helpers.dict_attr];
       type_params = [tvar];

jscomp/ml/typecore.ml

@@ -806,7 +806,7 @@ end) = struct
     Env.mark_type_used env (Path.last tpath) (Env.find_type tpath env);
     let is_dict = Path.same tpath Predef.path_dict in
     if is_dict then (
-      (* [dict] Dicts are implented as a record with a single "magic" field. This magic field is 
+      (* [dict] Dicts are implemented as a record with a single "magic" field. This magic field is 
          used to track the dict value type, and any label lookup on the dict record type 
          will give that single value type back. This is how we can piggy back on the record 
          pattern matching mechanism.