Add js.try_catch JS virtualization method

Author: LPTK

core/shared/main/scala/utils/package.scala

@@ -228,7 +228,8 @@ package object utils {
   def TODO(msg: Any, cond: Bool): Unit = if (cond) TODO(msg)
   def die: Nothing = lastWords("Program reached an unexpected state.")
   def lastWords(msg: String): Nothing = throw new Exception(s"Internal Error: $msg")
-  def wat(msg: String, wat: Any): Nothing = lastWords(s"$msg ($wat)")
+  def wat(msg: String, obj: Any): Nothing = lastWords(s"$msg ($obj)")
+  def wat(obj: Any): Nothing = wat(s"unexpected value", obj)
 
   /** To make Scala unexhaustivity warnings believed to be spurious go away,
    * while clearly indicating the intent. */

hkmc2/shared/src/main/scala/hkmc2/codegen/Lowering.scala

@@ -190,6 +190,12 @@ class Lowering()(using Config, TL, Raise, State, Ctx):
       }(Nil)
     case ref @ st.Ref(sym) =>
       sym match
+      case ctx.builtins.source.bms | ctx.builtins.js.bms =>
+        raise:
+          ErrorReport(
+            msg"Module '${sym.nme}' is virtual (i.e., \"compiler fiction\"); cannot be used directly" -> t.toLoc ::
+            Nil, S(t), source = Diagnostic.Source.Compilation)
+        return End("error")
       case sym: BuiltinSymbol =>
         warnStmt
         if sym.binary then
@@ -318,6 +324,8 @@ class Lowering()(using Config, TL, Raise, State, Ctx):
           subTerm_nonTail(arg): ar =>
             k(Call(fr, Arg(spread = true, ar) :: Nil)(isMlsFun, true))
       f match
+      case t if t.symbol.isDefined && (t.symbol.get is ctx.builtins.js.try_catch) =>
+        conclude(Value.Ref(State.runtimeSymbol).selN(Tree.Ident("try_catch")))
       // * Due to whacky JS semantics, we need to make sure that selections leading to a call
       // * are preserved in the call and not moved to a temporary variable.
       case sel @ Sel(prefix, nme) =>

hkmc2/shared/src/main/scala/hkmc2/semantics/Elaborator.scala

@@ -103,15 +103,20 @@ object Elaborator:
       val Object = assumeBuiltinCls("Object")
       val untyped = assumeBuiltinTpe("untyped")
       // println(s"Builtins: $Int, $Num, $Str, $untyped")
-      object source:
-        private val module = assumeBuiltinMod("source")
-        private def assumeObject(nme: Str): BlockMemberSymbol =
+      class VirtualModule(val module: ModuleSymbol):
+        val bms = getBuiltin(module.nme) match
+          case S(Ctx.RefElem(bms: BlockMemberSymbol)) => bms
+          case huh => wat(huh)
+        protected def assumeObject(nme: Str): BlockMemberSymbol =
           module.tree.definedSymbols.get(nme).getOrElse:
             throw new NoSuchElementException:
               s"builtin module symbol source.$nme. we have"
+      object source extends VirtualModule(assumeBuiltinMod("source")):
         val line = assumeObject("line")
         val name = assumeObject("name")
         val file = assumeObject("file")
+      object js extends VirtualModule(assumeBuiltinMod("js")):
+        val try_catch = assumeObject("try_catch")
       def getBuiltinOp(op: Str): Opt[Str] =
         if getBuiltin(op).isDefined then builtinBinOps.get(op) else N
       /** Classes that do not use `instanceof` in pattern matching. */

hkmc2/shared/src/test/mlscript-compile/Iter.mjs

@@ -307,7 +307,7 @@ Iter1 = class Iter {
     next = tmp1;
     scrut = next.done;
     if (scrut === true) {
-      throw new globalThis.Error.class("Empty iterator");
+      throw new globalThis.Error("Empty iterator");
     } else {
       tmp2 = runtime.Unit;
     }

hkmc2/shared/src/test/mlscript-compile/Runtime.mjs

@@ -1,4 +1,5 @@
 import runtime from "./Runtime.mjs";
+import RuntimeJS from "./RuntimeJS.mjs";
 let Runtime1;
 Runtime1 = class Runtime {
   static {
@@ -10,6 +11,7 @@ Runtime1 = class Runtime {
     };
     this.Unit = new Unit$class;
     this.Unit.class = Unit$class;
+    this.try_catch = RuntimeJS.try_catch;
     this.MatchResult = function MatchResult(captures1) {
       return new MatchResult.class(captures1);
     };

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

@@ -1,3 +1,4 @@
+import "./RuntimeJS.mjs" 
 
 
 module Runtime with ...
@@ -20,6 +21,9 @@ fun deboundMethod(mtdName, clsName) =
     "[debinding error] Method '" + mtdName + "' of class '" + clsName + "' was accessed without being called."
 
 
+val try_catch = RuntimeJS.try_catch
+
+
 // For `pattern` definitions
 class MatchResult(captures)
 class MatchFailure(errors)

hkmc2/shared/src/test/mlscript-compile/RuntimeJS.mjs

@@ -0,0 +1,10 @@
+
+const RuntimeJS = {
+  try_catch(computation, onError) {
+    try { return computation() }
+    catch (error) { return onError(error) }
+  }
+}
+
+export default RuntimeJS;
+

hkmc2/shared/src/test/mlscript/bbml/bbPrelude.mls

@@ -29,12 +29,16 @@ declare class Str(length: Int, concat: Str -> Str)
 
 declare class Error(msg: Str)
 
-declare module Predef
 
 declare module source with
-  object line: Int
-  object name: Str
-  object file: Str
+  object
+    line: Int
+    name: Str
+    file: Str
+
+declare module js with
+  fun try_catch
+
 
 declare fun run: [T] -> CodeBase[out T, out Nothing, out Any] -> T
 declare fun log: Str -> Any

hkmc2/shared/src/test/mlscript/decls/Prelude.mls

@@ -15,8 +15,8 @@ declare class String
 declare class RegExp
 declare class Set
 declare class Map
-declare class Error(msg)
-declare class TypeError(msg)
+declare class Error
+declare class TypeError
 declare class Symbol
 
 // MLscript-specific types
@@ -49,4 +49,8 @@ declare module source with
     name
     file
 
+declare module js with
+  fun
+    try_catch
+
 

hkmc2/shared/src/test/mlscript/interop/Virtualization.mls

@@ -0,0 +1,29 @@
+:js
+
+
+// * `try`/`catch`
+
+js.try_catch(() => 123, id)
+//│ = 123
+
+js.try_catch(() => 123(), id)
+//│ = TypeError: 123 is not a function
+
+js.try_catch of
+  () => 123()
+  case { TypeError then 666, e then throw e }
+//│ = 666
+
+:re
+js.try_catch of
+  () => throw Error("whoops")
+  case TypeError then 666
+//│ ═══[RUNTIME ERROR] Error: match error
+
+:re
+js.try_catch of
+  () => throw Error("whoops")
+  case { TypeError then 666, e then throw e }
+//│ ═══[RUNTIME ERROR] Error: whoops
+
+