Record spread and never type (#2737)

CHANGES.md

@@ -18,6 +18,8 @@ New:
   - `file.replaygain` to compute the replaygain of a file
 - Added support for ImageLib to decode images.
 - Added support for completion in emacs based on company (#2652).
+- Added syntactic sugar for record spread: `let {foo, gni, ..y} = x`
+  and `y = { foo = 123, gni = "aabb", ...x}` (#2737)
 
 Changed:
 

doc/content/language.md

@@ -879,6 +879,26 @@ the duration with
 print("The duration of the song is #{song.duration} seconds")
 ```
 
+Records can be re-used using _spreads_:
+
+```liquidsoap
+song = { filename = "song.mp3", duration = 257., bpm = 132. }
+
+# This is a fresh value with all the fields from `song` and
+# a new `id` field:
+song_with_id = { id = 1234, ...song }
+```
+
+Alternatively, you can also extend a record using the explicit `v.{...}` syntax:
+
+```liquidsoap
+song = { filename = "song.mp3", duration = 257., bpm = 132. }
+
+# This is a fresh value with all the fields from `song` and
+# a new `id` field:
+song_with_id = song.{id = 1234}
+```
+
 ### Modules
 
 Records are heavily used in Liquidsoap in order to structure the functions of
@@ -1072,6 +1092,10 @@ Here are some examples:
 let {foo, bar} = {foo = 123, bar = "baz", gni = true}
 # foo = 123, bar = "baz"
 
+# Record capture with spread
+let {foo, bar, ...x} = {foo = 123, bar = "baz", gni = true}
+# foo = 123, bar = "baz", x = {gni = true}
+
 # Module capture
 let v.{foo, bar} = "aabbcc".{foo = 123, bar = "baz", gni = true}
 # v = "aabbcc", foo = 123, bar = "baz"

src/lang/evaluation.ml

@@ -84,6 +84,14 @@ let rec eval_pat pat v =
           @ env
       | PMeth (pat, l), _ ->
           let m, v = Value.split_meths v in
+          let fields = List.map fst l in
+          let v =
+            List.fold_left
+              (fun v (l, m) ->
+                if List.mem l fields then v
+                else { v with Value.value = Meth (l, m, v) })
+              v m
+          in
           let env = match pat with None -> env | Some pat -> aux env pat v in
           List.fold_left
             (fun env (lbl, pat) ->

src/lang/parser.mly

@@ -217,6 +217,9 @@ expr:
   | LPAR RPAR                        { mk ~pos:$loc (Tuple []) }
   | LPAR inner_tuple RPAR            { mk ~pos:$loc (Tuple $2) }
   | expr DOT LCUR record RCUR        { $4 ~pos:$loc $1 }
+  | LCUR DOTDOTDOT expr RCUR         { $3 }
+  | LCUR record COMMA DOTDOTDOT expr RCUR
+                                     { $2 ~pos:$loc $5 }
   | LCUR record RCUR                 { $2 ~pos:$loc (mk ~pos:$loc (Tuple [])) }
   | LCUR RCUR                        { mk ~pos:$loc (Tuple []) }
   | expr QUESTION DOT invoke         { mk_invoke ~pos:$loc ~default:(mk ~pos:$loc Null) $1 $4 }
@@ -428,7 +431,15 @@ meth_pattern_list:
 record_pattern:
   | LCUR meth_pattern_list RCUR { $2 }
 
+meth_spread_list:
+  | DOTDOTDOT VAR                          { Some (PVar [$2]), [] }
+  | meth_pattern_el COMMA meth_spread_list { fst $3, $1::(snd $3) }
+
+record_spread_pattern:
+  | LCUR meth_spread_list RCUR { $2 }
+
 meth_pattern:
+  | record_spread_pattern            { PMeth $1                      }
   | record_pattern                   { PMeth (None,              $1) }
   | VAR DOT record_pattern           { PMeth (Some (PVar [$1]),  $3) }
   | UNDERSCORE DOT record_pattern    { PMeth (Some (PVar ["_"]), $3) }

src/lang/term.ml

@@ -532,8 +532,6 @@ end
 
 module MkAbstract (Def : AbstractDef) = struct
   module T = Type.Ground.Make (struct
-    type t
-
     let name = Def.name
   end)
 

src/lang/typechecking.ml

@@ -96,6 +96,14 @@ let rec type_of_pat ~level ~pos = function
           | None -> ([], Type.make ?pos (Type.Tuple []))
           | Some pat -> type_of_pat ~level ~pos pat
       in
+      Typing.(
+        ty
+        <: List.fold_left
+             (fun ty (label, _) ->
+               Type.meth ~optional:true label
+                 ([], Type.make ?pos Ground_type.never)
+                 ty)
+             (Type.var ~level ?pos ()) l);
       let env, ty =
         List.fold_left
           (fun (env, ty) (lbl, p) ->

src/lang/types/ground_type.ml

@@ -21,8 +21,6 @@
  *****************************************************************************)
 
 module type Spec = sig
-  type t
-
   val name : string
 end
 
@@ -69,34 +67,32 @@ module Make (S : Spec) = struct
 end
 
 module Int = Make (struct
-  type t = int
-
   let name = "int"
 end)
 
 let int = Int.descr
 
 module Float = Make (struct
-  type t = float
-
   let name = "float"
 end)
 
 let float = Float.descr
 
 module String = Make (struct
-  type t = string
-
   let name = "string"
 end)
 
 let string = String.descr
 
 module Bool = Make (struct
-  type t = bool
-
   let name = "bool"
 end)
 
 let bool = Bool.descr
+
+module Never = Make (struct
+  let name = "never"
+end)
+
+let never = Never.descr
 let is_ground v = List.mem v !types

src/lang/types/ground_type.mli

@@ -21,8 +21,6 @@
  *****************************************************************************)
 
 module type Spec = sig
-  type t
-
   val name : string
 end
 
@@ -48,4 +46,8 @@ val string : Type_base.descr
 module Bool : Custom
 
 val bool : Type_base.descr
+
+module Never : Custom
+
+val never : Type_base.descr
 val is_ground : Type_base.custom -> bool

tests/language/record.liq

@@ -173,6 +173,43 @@ def f() =
   test.equals(f({ foo = (fun (_) -> { gni = 2 } ) }), 2)
   test.equals(f(456.{ foo = (fun (_) -> true.{ gni = 2 } ) }), 2)
 
+  # Spread patterns:
+  x = { foo = 123, gni = "aabb" }
+  let { foo, ...y } = x
+  test.equals(foo, 123)
+  test.equals(y.gni, "aabb")
+  test.equals(y, ())
+  test.equals(y?.foo, null())
+
+  x = 1.{ foo = 123, gni = "aabb" }
+  let { foo, ...y } = x
+  test.equals(foo, 123)
+  test.equals(y.gni, "aabb")
+  test.equals(y, 1)
+  test.equals(y?.foo, null())
+
+  x = 1.{ foo = 123, gni = "aabb" }
+  let y.{ foo } = x
+  test.equals(foo, 123)
+  test.equals(y.gni, "aabb")
+  test.equals(y, 1)
+  test.equals(y?.foo, null())
+
+  x = {foo = 3.14}.{ foo = 123, gni = "aabb" }
+  let { foo, ...y } = x
+  test.equals(foo, 123)
+  test.equals(y.gni, "aabb")
+  test.equals(y, ())
+  test.equals(y?.foo, null())
+
+  x = { foo = 123, gni = "aabb" }
+  y = { bla = 3.14, ...x }
+  test.equals(y, { foo = 123, gni = "aabb", bla = 3.14 })
+
+  x = 1.{ foo = 123, gni = "aabb" }
+  y = { bla = 3.14, ...x }
+  test.equals(y, 1.{ foo = 123, gni = "aabb", bla = 3.14 })
+
   test.pass()
 end
 

tests/language/type_errors.liq

@@ -210,6 +210,14 @@ def f() =
   correct("fun (x) -> x.foo.gni?.bla(1,2,3).blo")
   correct("fun (x) -> x?.foo(123).gni ?? null()")
 
+  section("PATTERNS")
+  incorrect("
+  def f(x) =
+    let y.{foo} = x
+    y.foo + 1
+    end
+  ")
+
   test.pass()
 end