Enforce rules on module parameters

Author: FlandiaYingman

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

@@ -638,8 +638,15 @@ extends Importer:
     else VarSymbol(id, nextUid)
 
   def param(t: Tree): Ctxl[Ls[Param]] = t match
-    case TypeDef(Mod, inner, N, N) => param(inner)
-      .map(p => p.copy(flags = p.flags.copy(mod = true)))
+    case TypeDef(Mod, inner, N, N) =>
+      val ps = param(inner).map(p => p.copy(flags = p.flags.copy(mod = true)))
+      for p <- ps if p.flags.mod do p.sign match
+        case N =>
+          raise(ErrorReport(msg"Module parameters must have explicit types." -> t.toLoc :: Nil))
+        case S(ret) if ModuleChecker.isTypeParam(ret) => 
+          raise(ErrorReport(msg"Module parameters must have concrete types." -> t.toLoc :: Nil))
+        case _ => ()
+      ps
     case _ => t.param.map: (p, t) =>
       Param(FldFlags.empty, fieldOrVarSym(ParamBind, p), t.map(term))
 
@@ -708,7 +715,15 @@ extends Importer:
     while trav.changed do
       trav.changed = false
       go(s)
+  
+  object ModuleChecker:
 
+    /** Checks if a term is a reference to a type parameter. */
+    def isTypeParam(t: Term): Bool = t.symbol
+      .filter(_.isInstanceOf[VarSymbol])
+      .flatMap(_.asInstanceOf[VarSymbol].decl)
+      .fold(false)(_.isInstanceOf[TyParam])
+  
   class VarianceTraverser(var changed: Bool = true) extends Traverser:
     override def traverseType(pol: Pol)(trm: Term): Unit = trm match
       case Term.TyApp(lhs, targs) =>

hkmc2/shared/src/test/mlscript/basics/ModuleMethods.mls

@@ -7,3 +7,18 @@ module M with {
   // module method foo
   fun foo(x) = x
 }
+
+:e
+fun f1(module m)
+//│ ╔══[ERROR] Module parameters must have explicit types.
+//│ ║  l.12: 	fun f1(module m)
+//│ ╙──      	              ^
+
+:e
+fun f2[T](module m: T)
+//│ ╔══[ERROR] Module parameters must have concrete types.
+//│ ║  l.18: 	fun f2[T](module m: T)
+//│ ╙──      	                 ^^^^
+
+
+fun ok1(module m: M)