Move UCS helper functions to the runtime module

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

@@ -26,17 +26,17 @@ trait DesugaringBase(using state: State):
   protected lazy val matchResultClass: Ctxl[(Term.Sel | Term.SynthSel, ClassSymbol)] =
     (State.runtimeSymbol.ref().selNoSym("MatchResult", synth=true), State.matchResultClsSymbol)
 
-  /** Make a pattern looks like `runtime.MatchResult.class`. */
+  /** Make a pattern that looks like `runtime.MatchResult.class`. */
   protected def matchResultPattern(parameters: Opt[List[BlockLocalSymbol]]): Ctxl[Pattern.ClassLike] =
     val (classRef, classSym) = matchResultClass
     val classSel = Term.SynthSel(classRef, Ident("class"))(S(classSym))
     Pattern.ClassLike(classSym, classSel, parameters, false)(Empty())
 
-  /** Make a term looks like `runtime.MatchFailure` with its symbol. */
+  /** Make a term that looks like `runtime.MatchFailure` with its symbol. */
   protected lazy val matchFailureClass: Ctxl[(Term.Sel | Term.SynthSel, ClassSymbol)] =
     (State.runtimeSymbol.ref().selNoSym("MatchFailure", synth=true), State.matchFailureClsSymbol)
 
-  /** Make a pattern looks like `runtime.MatchFailure.class`. */
+  /** Make a pattern that looks like `runtime.MatchFailure.class`. */
   protected def matchFailurePattern(parameters: Opt[List[BlockLocalSymbol]]): Ctxl[Pattern.ClassLike] =
     val (classRef, classSym) = matchResultClass
     val classSel = Term.SynthSel(classRef, Ident("class"))(S(classSym))

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

@@ -66,7 +66,9 @@ let Runtime1;
         return runtime.safeCall(globalThis.Array.prototype.slice.call(xs, i, tmp))
       } 
       static get(xs1, i1) {
-        return globalThis.Array.prototype.at.call(xs1, i1)
+        let tmp;
+        tmp = globalThis.Array.prototype.at.call(xs1, i1);
+        return Runtime.safeCall(tmp)
       }
       static toString() { return "Tuple"; }
     });

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

@@ -49,7 +49,7 @@ module Tuple with
 
   fun get(xs, i) =
     // * Contrary to `xs.[i]`, this supports negative indices (Python-style)
-    globalThis.Array.prototype.at.call(xs, i)
+    safeCall of globalThis.Array.prototype.at.call(xs, i)
 
 module Str with
   fun startsWith(string, prefix) = string.startsWith(prefix)

hkmc2/shared/src/test/mlscript/codegen/RuntimeUsage.mls

@@ -46,3 +46,38 @@ print of  checkCall(undefined)
 //│ ═══[RUNTIME ERROR] Error: MLscript call unexpectedly returned `undefined`, the forbidden value.
 
 
+print of Tuple.slice([1, 2, 3, 4], 1, -1)
+//│ > [2, 3, 4]
+
+print of Tuple.get([1, 2, 3, 4], 0)
+//│ > 1
+
+print of Tuple.get([1, 2, 3, 4], -1)
+//│ > 4
+
+print of Tuple.get([1, 2, 3, 4], 5)
+//│ > ()
+
+print of Str.drop("hello, world", 2)
+//│ > llo, world
+
+print of Str.drop("hello, world", -2)
+//│ > ld
+
+print of Str.get("hello, world", 2)
+//│ > l
+
+print of Str.get("hello, world", 22)
+//│ > ()
+
+print of Str.get("hello, world", -1)
+//│ > d
+
+print of Str.startsWith("hello, world", "hello")
+//│ > true
+
+print of Str.startsWith("hello, world", "")
+//│ > true
+
+print of Str.startsWith("hello, world", "farewell")
+//│ > false