fix #18 basic exceptions handling

docs/tutorial.md

@@ -753,6 +753,34 @@ We can use labels too:
     assert( search(["hello", "world"], 'z') == null)
     >>> void
 
+# Exception handling
+
+Very much like in Kotlin. Try block returns its body block result, if no exception was cauht, or the result from the catch block that caught the exception:
+
+    var error = "not caught"
+    var finallyCaught = false
+    val result = try {
+        throw IllegalArgumentException()
+        "invalid"
+    }
+    catch(nd: SymbolNotDefinedException) {
+        error = "bad catch"
+    }
+    catch(x: IllegalArgumentException) {
+        error = "no error"
+        "OK"
+    }
+    finally {
+        // finally does not affect returned value
+        "too bad"
+    }
+    assertEquals( "no error", error)
+    assertEquals( "OK", result)
+    >>> void
+
+It is possible to catch several exceptions in the same block (TBD)
+
+
 # Self-assignments in expression
 
 There are auto-increments and auto-decrements:

library/build.gradle.kts

@@ -5,7 +5,7 @@ import org.jetbrains.kotlin.gradle.ExperimentalWasmDsl
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 group = "net.sergeych"
-version = "0.4.0-SNAPSHOT"
+version = "0.5.0-SNAPSHOT"
 
 buildscript {
     repositories {
@@ -62,6 +62,7 @@ kotlin {
     sourceSets {
         all {
             languageSettings.optIn("kotlinx.coroutines.ExperimentalCoroutinesApi")
+            languageSettings.optIn("kotlin.contracts.ExperimentalContracts::class")
             languageSettings.optIn("kotlin.ExperimentalUnsignedTypes")
             languageSettings.optIn("kotlin.coroutines.DelicateCoroutinesApi")
         }

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

@@ -717,10 +717,115 @@ class Compiler(
         "fn", "fun" -> parseFunctionDeclaration(cc)
         "if" -> parseIfStatement(cc)
         "class" -> parseClassDeclaration(cc, false)
-        "struct" -> parseClassDeclaration(cc, true)
+        "try" -> parseTryStatement(cc)
+        "throw" -> parseThrowStatement(cc)
         else -> null
     }
 
+    private fun parseThrowStatement(cc: CompilerContext): Statement {
+        val throwStatement = parseStatement(cc) ?: throw ScriptError(cc.currentPos(), "throw object expected")
+        return statement {
+            val errorObject = throwStatement.execute(this)
+            if( errorObject is ObjException )
+                raiseError(errorObject)
+            else raiseError("this is not an exception object: $errorObject")
+        }
+    }
+
+    private data class CatchBlockData(
+        val catchVar: Token,
+        val classNames: List<String>,
+        val block: Statement
+    )
+
+    private fun parseTryStatement(cc: CompilerContext): Statement {
+        val body = parseBlock(cc)
+        val catches = mutableListOf<CatchBlockData>()
+        cc.skipTokens(Token.Type.NEWLINE)
+        var t = cc.next()
+        while( t.value == "catch" ) {
+            ensureLparen(cc)
+            t = cc.next()
+            if( t.type != Token.Type.ID ) throw ScriptError(t.pos, "expected catch variable")
+            val catchVar = t
+            cc.skipTokenOfType(Token.Type.COLON)
+            // load list of exception classes
+            val exClassNames = mutableListOf<String>()
+            do {
+                t = cc.next()
+                if( t.type != Token.Type.ID )
+                    throw ScriptError(t.pos, "expected exception class name")
+                exClassNames += t.value
+                t = cc.next()
+                when(t.type) {
+                    Token.Type.COMMA -> {
+                        continue
+                    }
+                    Token.Type.RPAREN -> {
+                        break
+                    }
+                    else -> throw ScriptError(t.pos, "syntax error: expected ',' or ')'")
+                }
+            } while(true)
+            val block = parseBlock(cc)
+            catches += CatchBlockData(catchVar, exClassNames, block)
+            cc.skipTokens(Token.Type.NEWLINE)
+            t = cc.next()
+        }
+        if( catches.isEmpty() )
+            throw ScriptError(cc.currentPos(), "try block must have at least one catch clause")
+        val finallyClause = if( t.value == "finally" ) {
+            parseBlock(cc)
+        } else {
+            cc.previous()
+            null
+        }
+
+        return statement {
+            var result: Obj = ObjVoid
+            try {
+                // body is a parsed block, it already has separate context
+                result = body.execute(this)
+            }
+            catch (e: Exception) {
+                // convert to appropriate exception
+                val objException = when(e) {
+                    is ExecutionError -> e.errorObject
+                    else -> ObjUnknownException(this, e.message ?: e.toString())
+                }
+                // let's see if we should catch it:
+                var isCaught = false
+                for( cdata in catches ) {
+                    var exceptionObject: ObjException? = null
+                    for (exceptionClassName in cdata.classNames) {
+                        val exObj = ObjException.getErrorClass(exceptionClassName)
+                            ?: raiseSymbolNotFound("error clas not exists: $exceptionClassName")
+                        println("exObj: $exObj")
+                        println("objException: ${objException.objClass}")
+                        if( objException.objClass == exObj )
+                            exceptionObject = objException
+                            break
+                    }
+                    if( exceptionObject != null ) {
+                        val catchContext = this.copy(pos = cdata.catchVar.pos)
+                        catchContext.addItem(cdata.catchVar.value, false, objException)
+                        result = cdata.block.execute(catchContext)
+                        isCaught = true
+                        break
+                    }
+                }
+                // rethrow if not caught this exception
+                if( !isCaught )
+                    throw e
+            }
+            finally {
+                // finally clause does not alter result!
+                finallyClause?.execute(this)
+            }
+            result
+        }
+    }
+
     private fun parseClassDeclaration(cc: CompilerContext, isStruct: Boolean): Statement {
         val nameToken = cc.requireToken(Token.Type.ID)
         val constructorArgsDeclaration =

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

@@ -16,27 +16,27 @@ class Context(
     fun raiseNotImplemented(what: String = "operation"): Nothing = raiseError("$what is not implemented")
 
     @Suppress("unused")
-    fun raiseNPE(): Nothing = raiseError(ObjNullPointerError(this))
+    fun raiseNPE(): Nothing = raiseError(ObjNullPointerException(this))
 
     @Suppress("unused")
     fun raiseIndexOutOfBounds(message: String = "Index out of bounds"): Nothing =
-        raiseError(ObjIndexOutOfBoundsError(this, message))
+        raiseError(ObjIndexOutOfBoundsException(this, message))
 
     @Suppress("unused")
     fun raiseArgumentError(message: String = "Illegal argument error"): Nothing =
-        raiseError(ObjIllegalArgumentError(this, message))
+        raiseError(ObjIllegalArgumentException(this, message))
 
-    fun raiseClassCastError(msg: String): Nothing = raiseError(ObjClassCastError(this, msg))
+    fun raiseClassCastError(msg: String): Nothing = raiseError(ObjClassCastException(this, msg))
 
     @Suppress("unused")
     fun raiseSymbolNotFound(name: String): Nothing =
-        raiseError(ObjSymbolNotDefinedError(this, "symbol is not defined: $name"))
+        raiseError(ObjSymbolNotDefinedException(this, "symbol is not defined: $name"))
 
     fun raiseError(message: String): Nothing {
-        throw ExecutionError(ObjError(this, message))
+        throw ExecutionError(ObjException(this, message))
     }
 
-    fun raiseError(obj: ObjError): Nothing {
+    fun raiseError(obj: ObjException): Nothing {
         throw ExecutionError(obj)
     }
 

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

@@ -4,7 +4,10 @@ import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
+import net.sergeych.bintools.encodeToHex
 import net.sergeych.synctools.ProtectedOp
+import net.sergeych.synctools.withLock
+import kotlin.contracts.ExperimentalContracts
 
 /**
  * Record to store object with access rules, e.g. [isMutable] and access level [visibility].
@@ -63,7 +66,7 @@ open class Obj {
     suspend fun invokeInstanceMethod(context: Context, name: String, vararg args: Obj): Obj =
         invokeInstanceMethod(context, name, Arguments(args.toList()))
 
-    inline suspend fun <reified T : Obj> callMethod(
+    suspend inline fun <reified T : Obj> callMethod(
         context: Context,
         name: String,
         args: Arguments = Arguments.EMPTY
@@ -179,11 +182,10 @@ open class Obj {
 
     suspend fun <T> sync(block: () -> T): T = monitor.withLock { block() }
 
-    suspend open fun readField(context: Context, name: String): ObjRecord {
+    open suspend fun readField(context: Context, name: String): ObjRecord {
         // could be property or class field:
         val obj = objClass.getInstanceMemberOrNull(name) ?: context.raiseError("no such field: $name")
-        val value = obj.value
+        return when (val value = obj.value) {
-        return when (value) {
             is Statement -> {
                 ObjRecord(value.execute(context.copy(context.pos, newThisObj = this)), obj.isMutable)
             }
@@ -327,21 +329,97 @@ data class ObjNamespace(val name: String) : Obj() {
     }
 }
 
-open class ObjError(val context: Context, val message: String) : Obj() {
+open class ObjException(exceptionClass: ExceptionClass, val context: Context, val message: String) : Obj() {
-    override val asStr: ObjString by lazy { ObjString("Error: $message") }
+    constructor(name: String,context: Context, message: String) : this(getOrCreateExceptionClass(name), context, message)
+    constructor(context: Context, message: String) : this(Root, context, message)
 
     fun raise(): Nothing {
         throw ExecutionError(this)
     }
+
+    override val objClass: ObjClass = exceptionClass
+
+    override fun toString(): String {
+        return "ObjException:${objClass.className}:${context.pos}@${hashCode().encodeToHex()}"
+    }
+
+    companion object {
+
+        class ExceptionClass(val name: String,vararg parents: ObjClass) : ObjClass(name, *parents) {
+            override suspend fun callOn(context: Context): Obj {
+                return ObjException(this, context, name).apply {
+                    println(">>>> "+this)
+                }
+            }
+            override fun toString(): String = "ExceptionClass[$name]@${hashCode().encodeToHex()}"
+        }
+        val Root = ExceptionClass("Throwable")
+
+        private val op = ProtectedOp()
+        private val existingErrorClasses = mutableMapOf<String, ExceptionClass>()
+
+
+        @OptIn(ExperimentalContracts::class)
+        protected fun getOrCreateExceptionClass(name: String): ExceptionClass {
+            return op.withLock {
+                existingErrorClasses.getOrPut(name) {
+                    ExceptionClass(name, Root)
+                }
+            }
+        }
+
+        /**
+         * Get [ObjClass] for error class by name if exists.
+         */
+        @OptIn(ExperimentalContracts::class)
+        fun getErrorClass(name: String): ObjClass? = op.withLock {
+            existingErrorClasses[name]
+        }
+
+        fun addExceptionsToContext(context: Context) {
+            context.addConst("Exception", Root)
+            existingErrorClasses["Exception"] = Root
+            for (name in listOf(
+                "NullPointerException",
+                "AssertionFailedException",
+                "ClassCastException",
+                "IndexOutOfBoundsException",
+                "IllegalArgumentException",
+                "IllegalAssignmentException",
+                "SymbolNotDefinedException",
+                "IterationEndException",
+                "AccessException",
+                "UnknownException",
+            )) {
+                context.addConst(name, getOrCreateExceptionClass(name))
+            }
+        }
+    }
 }
 
-class ObjNullPointerError(context: Context) : ObjError(context, "object is null")
+class ObjNullPointerException(context: Context) : ObjException("NullPointerException", context, "object is null")
 
-class ObjAssertionError(context: Context, message: String) : ObjError(context, message)
+class ObjAssertionFailedException(context: Context, message: String) :
-class ObjClassCastError(context: Context, message: String) : ObjError(context, message)
+    ObjException("AssertionFailedException", context, message)
-class ObjIndexOutOfBoundsError(context: Context, message: String = "index out of bounds") : ObjError(context, message)
+
-class ObjIllegalArgumentError(context: Context, message: String = "illegal argument") : ObjError(context, message)
+class ObjClassCastException(context: Context, message: String) : ObjException("ClassCastException", context, message)
-class ObjIllegalAssignmentError(context: Context, message: String = "illegal assignment") : ObjError(context, message)
+class ObjIndexOutOfBoundsException(context: Context, message: String = "index out of bounds") :
-class ObjSymbolNotDefinedError(context: Context, message: String = "symbol is not defined") : ObjError(context, message)
+    ObjException("IndexOutOfBoundsException", context, message)
-class ObjIterationFinishedError(context: Context) : ObjError(context, "iteration finished")
+
-class ObjAccessError(context: Context, message: String = "access not allowed error") : ObjError(context, message)
+class ObjIllegalArgumentException(context: Context, message: String = "illegal argument") :
+    ObjException("IllegalArgumentException", context, message)
+
+class ObjIllegalAssignmentException(context: Context, message: String = "illegal assignment") :
+    ObjException("IllegalAssignmentException", context, message)
+
+class ObjSymbolNotDefinedException(context: Context, message: String = "symbol is not defined") :
+    ObjException("SymbolNotDefinedException", context, message)
+
+class ObjIterationFinishedException(context: Context) :
+    ObjException("IterationEndException", context, "iteration finished")
+
+class ObjAccessException(context: Context, message: String = "access not allowed error") :
+    ObjException("AccessException", context, message)
+
+class ObjUnknownException(context: Context, message: String = "access not allowed error") :
+    ObjException("UnknownException", context, message)

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

@@ -2,7 +2,7 @@ package net.sergeych.lyng
 
 val ObjClassType by lazy { ObjClass("Class") }
 
-class ObjClass(
+open class ObjClass(
     val className: String,
     vararg val parents: ObjClass,
 ) : Obj() {
@@ -122,7 +122,7 @@ class ObjArrayIterator(val array: Obj) : Obj() {
                     val self = thisAs<ObjArrayIterator>()
                     if (self.nextIndex < self.lastIndex) {
                         self.array.invokeInstanceMethod(this, "getAt", (self.nextIndex++).toObj())
-                    } else raiseError(ObjIterationFinishedError(this))
+                    } else raiseError(ObjIterationFinishedException(this))
                 }
                 addFn("hasNext") {
                     val self = thisAs<ObjArrayIterator>()

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

@@ -9,7 +9,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
             if (it.visibility.isPublic)
                 it
             else
-                context.raiseError(ObjAccessError(context, "can't access non-public field $name"))
+                context.raiseError(ObjAccessException(context, "can't access non-public field $name"))
         }
             ?: super.readField(context, name)
     }
@@ -17,8 +17,8 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
     override suspend fun writeField(context: Context, name: String, newValue: Obj) {
         instanceContext[name]?.let { f ->
             if (!f.visibility.isPublic)
-                ObjIllegalAssignmentError(context, "can't assign to non-public field $name")
+                ObjIllegalAssignmentException(context, "can't assign to non-public field $name")
-            if (!f.isMutable) ObjIllegalAssignmentError(context, "can't reassign val $name").raise()
+            if (!f.isMutable) ObjIllegalAssignmentException(context, "can't reassign val $name").raise()
             if (f.value.assign(context, newValue) == null)
                 f.value = newValue
         } ?: super.writeField(context, name, newValue)
@@ -29,7 +29,7 @@ class ObjInstance(override val objClass: ObjClass) : Obj() {
             if (it.visibility.isPublic)
                 it.value.invoke(context, this, args)
             else
-                context.raiseError(ObjAccessError(context, "can't invoke non-public method $name"))
+                context.raiseError(ObjAccessException(context, "can't invoke non-public method $name"))
         }
             ?: super.invokeInstanceMethod(context, name, args)
 

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

@@ -33,7 +33,7 @@ class ObjRangeIterator(val self: ObjRange) : Obj() {
             if( isCharRange ) ObjChar(x.toInt().toChar()) else ObjInt(x)
         }
         else {
-            context.raiseError(ObjIterationFinishedError(context))
+            context.raiseError(ObjIterationFinishedException(context))
         }
 
     companion object {

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

@@ -21,6 +21,7 @@ class Script(
 
     companion object {
         val defaultContext: Context = Context().apply {
+            ObjException.addExceptionsToContext(this)
             addFn("println") {
                 for ((i, a) in args.withIndex()) {
                     if (i > 0) print(' ' + a.asStr.value)
@@ -117,14 +118,14 @@ class Script(
             addVoidFn("assert") {
                 val cond = requiredArg<ObjBool>(0)
                 if( !cond.value == true )
-                    raiseError(ObjAssertionError(this,"Assertion failed"))
+                    raiseError(ObjAssertionFailedException(this,"Assertion failed"))
             }
 
             addVoidFn("assertEquals") {
                 val a = requiredArg<Obj>(0)
                 val b = requiredArg<Obj>(1)
                 if( a.compareTo(this, b) != 0 )
-                    raiseError(ObjAssertionError(this,"Assertion failed: ${a.inspect()} == ${b.inspect()}"))
+                    raiseError(ObjAssertionFailedException(this,"Assertion failed: ${a.inspect()} == ${b.inspect()}"))
             }
             addFn("assertThrows") {
                 val code = requireOnlyArg<Statement>()
@@ -138,7 +139,7 @@ class Script(
                 catch (e: ScriptError) {
                     ObjNull
                 }
-                result ?: raiseError(ObjAssertionError(this,"Expected exception but nothing was thrown"))
+                result ?: raiseError(ObjAssertionFailedException(this,"Expected exception but nothing was thrown"))
             }
 
             addVoidFn("delay") {

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

@@ -12,4 +12,4 @@ open class ScriptError(val pos: Pos, val errorMessage: String,cause: Throwable?=
     cause
 )
 
-class ExecutionError(val errorObject: ObjError) : ScriptError(errorObject.context.pos, errorObject.message)
+class ExecutionError(val errorObject: ObjException) : ScriptError(errorObject.context.pos, errorObject.message)

library/src/commonTest/kotlin/ScriptTest.kt

@@ -1748,4 +1748,36 @@ class ScriptTest {
         """
         )
     }
+
+    @Test
+    fun testThrowExisting()= runTest {
+        eval("""
+            val x = IllegalArgumentException("test")
+            println("instance class",x::class)
+            println("instance", x)
+            println("Exception object",Exception)
+            println("... and it's class",Exception::class)
+            assert( x is Exception )
+            println(x)
+
+            var t = 0
+            var finallyCaught = false
+            try {
+                t = 1
+                throw x
+                t = 2
+            }
+            catch( e: SymbolNotDefinedException ) {
+                t = 101
+            }
+            catch( e: IllegalArgumentException ) {
+                t = 3
+            }
+            finally {
+                finallyCaught = true
+            }
+            assertEquals(3, t)
+            assert(finallyCaught)
+        """.trimIndent())
+    }
 }