more dics & minor bugs fixed

library/src/commonMain/kotlin/net/sergeych/lyng/ArgsDeclaration.kt

@@ -8,6 +8,13 @@ data class ArgsDeclaration(val args: List<Item>, val endTokenType: Token.Type) {
     init {
         val i = args.count { it.isEllipsis }
         if (i > 1) throw ScriptError(args[i].pos, "there can be only one argument")
+        val start = args.indexOfFirst { it.defaultValue != null }
+        if (start >= 0)
+            for (j in start + 1 until args.size)
+                if (args[j].defaultValue == null) throw ScriptError(
+                    args[j].pos,
+                    "required argument can't follow default one"
+                )
     }
 
     /**
@@ -61,7 +68,7 @@ data class ArgsDeclaration(val args: List<Item>, val endTokenType: Token.Type) {
         fun processEllipsis(index: Int, toFromIndex: Int) {
             val a = args[index]
             val l = if (index > toFromIndex) ObjList()
-            else ObjList( fromArgs.values.subList(index, toFromIndex+1).toMutableList())
+            else ObjList(fromArgs.values.subList(index, toFromIndex + 1).toMutableList())
             assign(a, l)
         }
 
@@ -69,9 +76,8 @@ data class ArgsDeclaration(val args: List<Item>, val endTokenType: Token.Type) {
         if (leftIndex < args.size) {
             val end = processTail(leftIndex)
             processEllipsis(leftIndex, end)
-        }
-        else {
-            if( leftIndex < fromArgs.size)
+        } else {
+            if (leftIndex < fromArgs.size)
                 context.raiseArgumentError("too many arguments for the call")
         }
     }

library/src/commonMain/kotlin/net/sergeych/lyng/Script.kt

@@ -125,6 +125,20 @@ class Script(
                 if( a.compareTo(this, b) != 0 )
                     raiseError(ObjAssertionError(this,"Assertion failed: ${a.inspect()} == ${b.inspect()}"))
             }
+            addFn("assertThrows") {
+                val code = requireOnlyArg<Statement>()
+                val result =try {
+                    code.execute(this)
+                    null
+                }
+                catch( e: ExecutionError ) {
+                    e.errorObject
+                }
+                catch (e: ScriptError) {
+                    ObjNull
+                }
+                result ?: raiseError(ObjAssertionError(this,"Expected exception but nothing was thrown"))
+            }
 
             addVoidFn("delay") {
                 delay((this.args.firstAndOnly().toDouble()/1000.0).roundToLong())

library/src/jvmTest/kotlin/BookTest.kt

@@ -195,7 +195,7 @@ suspend fun DocTest.test(context: Context = Context()) {
             System.err.println("\nfailed: ${this.detailedString}")
         }
         error?.let {
-            fail("test failed", it)
+            fail(it.message, it)
         }
         assertEquals(expectedOutput, collectedOutput.toString(), "script output do not match")
         assertEquals(expectedResult, result.toString(), "script result does not match")
@@ -263,4 +263,9 @@ class BookTest {
             }
         }
     }
+
+    @Test
+    fun testArgumentBooks() = runTest {
+        runDocTests("../docs/declaring_arguments.md")
+    }
 }