Make minor fix to record pattern + misc

Author: LPTK

hkmc2/shared/src/main/scala/hkmc2/semantics/ucs/Desugarer.scala

@@ -612,9 +612,10 @@ class Desugarer(val elaborator: Elaborator)
         fallback
       case InfixApp(id: Ident, Keyword.`:`, pat) => fallback => ctx =>
         val sym = VarSymbol(id)
-        val ctxWithAlias = ctx + (id.name -> sym)
+        val ctx2 = ctx
+          // + (id.name -> sym) // * This binds the field's name in the context; probably surprising
         Split.Let(sym, ref.sel(id, N),
-          expandMatch(sym, pat, sequel)(fallback)(ctxWithAlias))
+          expandMatch(sym, pat, sequel)(fallback)(ctx2))
       case Block(st :: Nil) => fallback => ctx =>
         expandMatch(scrutSymbol, st, sequel)(fallback)(ctx)
       // case Block(sts) => fallback => ctx => // TODO

hkmc2/shared/src/test/mlscript-compile/Predef.mls

@@ -56,6 +56,7 @@ fun (???) notImplementedError = throw Error("Not implemented")
 
 fun tuple(...xs) = xs
 
+
 val foldl = fold
 
 // fun foldr(f)(...rest, init) = // TODO allow this syntax

hkmc2/shared/src/test/mlscript-compile/Record.mls

@@ -0,0 +1,15 @@
+
+import "./Predef.mls"
+open Predef
+
+import "./Iter.mls"
+
+
+module Record with...
+
+fun steal(from, ...fields) =
+  let rcd = new Object
+  fields Iter.each of f => set rcd.(f) = from.(f)
+  rcd
+
+

hkmc2/shared/src/test/mlscript/std/RecordTest.mls

@@ -0,0 +1,52 @@
+:js
+
+import "../../mlscript-compile/Record.mls"
+
+
+let src =
+  k0: 0
+  k1: 1
+  k2: 2
+  k3: 3
+  k4: 4
+//│ src = {k0: 0, k1: 1, k2: 2, k3: 3, k4: 4}
+
+src Record.steal("k1", "k2", "k3")
+//│ = {k1: 1, k2: 2, k3: 3}
+
+let dst =
+  k0: "0"
+  ...src Record.steal("k1", "k2", "k3")
+  k4: "4"
+//│ dst = {k0: "0", k1: 1, k2: 2, k3: 3, k4: "4"}
+
+
+// * Alternative 'cute' API
+
+import "../../mlscript-compile/Iter.mls"
+
+fun steal(...fields_from) =
+  let from = fields_from.at(-1).from
+  let fields = fields_from.slice(0, -1)
+  let rcd = new Object
+  fields Iter.each of f => set rcd.(f) = from.(f)
+  rcd
+
+let src =
+  k0: 0
+  k1: 1
+  k2: 2
+  k3: 3
+  k4: 4
+//│ src = {k0: 0, k1: 1, k2: 2, k3: 3, k4: 4}
+
+steal("k1", "k2", "k3", from: src)
+//│ = {k1: 1, k2: 2, k3: 3}
+
+let dst =
+  k0: "0"
+  ...steal("k1", "k2", "k3", from: src)
+  k4: "4"
+//│ dst = {k0: "0", k1: 1, k2: 2, k3: 3, k4: "4"}
+
+

hkmc2/shared/src/test/mlscript/ucs/patterns/RecordPattern.mls

@@ -20,3 +20,50 @@ fun take_1(p) =
 //│ ╙──      	       ^^^^^
 
 
+let f = case
+  { a: 1 as a } then a
+//│ f = [function]
+
+f(a: 1)
+//│ = 1
+
+
+// * It would probably be surprising to bind `a` in the RHS here
+:e
+let f = case
+  { a: 1 } then a
+//│ ╔══[ERROR] Name not found: a
+//│ ║  l.34: 	  { a: 1 } then a
+//│ ╙──      	                ^
+//│ f = [function]
+
+// * OTOH, note that `a` is bound here
+let rcd =
+  a: 1
+  b: a + 1
+//│ rcd = {a: 1, b: 2}
+
+// * As that will make sense when we have dependent types,
+// * as in: `{ n: Int, v: Vec[Int, n] }`
+
+
+:todo
+let f = case
+  { a: 1 & a } then a
+//│ ╔══[ERROR] Name not found: &
+//│ ║  l.52: 	  { a: 1 & a } then a
+//│ ╙──      	         ^
+//│ ╔══[ERROR] Cannot use this identifier as an extractor
+//│ ║  l.52: 	  { a: 1 & a } then a
+//│ ╙──      	         ^
+//│ f = [function]
+
+
+let f = case
+  { :a } then a
+//│ f = [function]
+
+f(a: 1)
+//│ = 1
+
+