support for Decimal.isInfitite and isNan

docs/Decimal.md

@@ -166,6 +166,17 @@ assertEquals(2.9, "2.9".d.toReal())
 
 Use `toReal()` only when you are willing to return to binary floating-point semantics.
 
+## Non-Finite Checks
+
+`Decimal` values are always finite, so these helpers exist for API symmetry with `Real` and always return `false`:
+
+```lyng
+import lyng.decimal
+
+assertEquals(false, "2.9".d.isInfinite())
+assertEquals(false, "2.9".d.isNaN())
+```
+
 ## Division Context
 
 Division is the operation where precision and rounding matter most.

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjDecimalSupport.kt

@@ -94,6 +94,12 @@ object ObjDecimalSupport {
         decimalClass.addFn("toReal") {
             ObjReal.of(valueOf(thisObj).doubleValue(false))
         }
+        decimalClass.addFn("isInfinite") {
+            ObjFalse
+        }
+        decimalClass.addFn("isNaN") {
+            ObjFalse
+        }
         decimalClass.addFn("toString") {
             ObjString(valueOf(thisObj).toStringExpanded())
         }

lynglib/src/commonMain/kotlin/net/sergeych/lyng/stdlib_included/decimal_lyng.kt

@@ -161,6 +161,10 @@ extern class Decimal() {
     extern fun toInt(): Int
     /** Convert to `Real`. */
     extern fun toReal(): Real
+    /** Return true if this decimal is positive or negative infinity. Always false for Decimal. */
+    extern fun isInfinite(): Bool
+    /** Return true if this decimal is NaN (not a number). Always false for Decimal. */
+    extern fun isNaN(): Bool
     /**
      * Convert to a plain decimal string without scientific notation.
      *

lynglib/src/commonTest/kotlin/net/sergeych/lyng/DecimalModuleTest.kt

@@ -51,6 +51,21 @@ class DecimalModuleTest {
         )
     }
 
+    @Test
+    fun testDecimalIsInfiniteAndIsNaN() = runTest {
+        val scope = Script.newScope()
+        scope.eval(
+            """
+            import lyng.decimal
+
+            assertEquals(false, 0.d.isInfinite())
+            assertEquals(false, "12.34".d.isInfinite())
+            assertEquals(false, 0.d.isNaN())
+            assertEquals(false, "12.34".d.isNaN())
+            """.trimIndent()
+        )
+    }
+
     @Test
     fun testDecimalModuleMixedIntOperators() = runTest {
         val scope = Script.newScope()