diff --git a/library/src/commonMain/kotlin/net/sergeych/ling/Compiler.kt b/library/src/commonMain/kotlin/net/sergeych/ling/Compiler.kt
index 62460bb..b8c75ce 100644
--- a/library/src/commonMain/kotlin/net/sergeych/ling/Compiler.kt
+++ b/library/src/commonMain/kotlin/net/sergeych/ling/Compiler.kt
@@ -97,6 +97,10 @@ class Compiler {
                             parseExpression(tokens)
                         }
                 }
+                Token.Type.PLUS2, Token.Type.MINUS2 -> {
+                    tokens.previous()
+                    parseExpression(tokens)
+                }
 
                 Token.Type.LABEL -> continue
                 Token.Type.SINLGE_LINE_COMMENT, Token.Type.MULTILINE_COMMENT -> continue
@@ -222,6 +226,25 @@ class Compiler {
                     throw ScriptError(t.pos, "Expected identifier after '.'")
             }
 
+            Token.Type.PLUS2 -> {
+                statement(id.pos) { context ->
+                    context.pos = id.pos
+                    val v = resolve(context).get(id.value)
+                        ?: throw ScriptError(id.pos, "Undefined symbol: ${id.value}")
+                    v.value?.getAndIncrement(context)
+                        ?: context.raiseNPE()
+                }
+            }
+
+            Token.Type.MINUS2 -> {
+                statement(id.pos) { context ->
+                    context.pos = id.pos
+                    val v = resolve(context).get(id.value)
+                        ?: throw ScriptError(id.pos, "Undefined symbol: ${id.value}")
+                    v.value?.getAndDecrement(context)
+                        ?: context.raiseNPE()
+                }
+            }
             Token.Type.LPAREN -> {
                 // function call
                 // Load arg list
@@ -243,10 +266,11 @@ class Compiler {
                         resolve(context).get(id.value) ?: throw ScriptError(id.pos, "Undefined function: ${id.value}")
                     (v.value as? Statement)?.execute(
                         context.copy(
+                            id.pos,
                             Arguments(
                                 nt.pos,
                                 args.map { Arguments.Info((it.value as Statement).execute(context), it.pos) }
-                            )
+                            ),
                         )
                     )
                         ?: throw ScriptError(id.pos, "Variable $id is not callable ($id)")
@@ -501,8 +525,9 @@ class Compiler {
         var closure: Context? = null
 
         val fnBody = statement(t.pos) { callerContext ->
+            callerContext.pos = start
             // restore closure where the function was defined:
-            val context = closure ?: Context()
+            val context = closure ?: callerContext.raiseError("bug: closure not set")
             // load params from caller context
             for ((i, d) in params.withIndex()) {
                 if (i < callerContext.args.size)
@@ -539,7 +564,7 @@ class Compiler {
         val block = parseScript(t.pos, tokens)
         return statement(t.pos) {
             // block run on inner context:
-            block.execute(it.copy())
+            block.execute(it.copy(t.pos))
         }.also {
             val t1 = tokens.next()
             if (t1.type != Token.Type.RBRACE)
diff --git a/library/src/commonMain/kotlin/net/sergeych/ling/Context.kt b/library/src/commonMain/kotlin/net/sergeych/ling/Context.kt
index 1d0e08d..47e8a94 100644
--- a/library/src/commonMain/kotlin/net/sergeych/ling/Context.kt
+++ b/library/src/commonMain/kotlin/net/sergeych/ling/Context.kt
@@ -1,9 +1,27 @@
 package net.sergeych.ling
 
 class Context(
-    val parent: Context? = Script.defaultContext.copy(),
-    val args: Arguments = Arguments.EMPTY
+    val parent: Context?,
+    val args: Arguments = Arguments.EMPTY,
+    var pos: Pos = Pos.builtIn
 ) {
+    constructor(
+        args: Arguments = Arguments.EMPTY,
+        pos: Pos = Pos.builtIn
+    )
+            : this(Script.defaultContext, args, pos)
+
+    fun raiseNotImplemented(): Nothing = raiseError("operation not implemented")
+
+    fun raiseNPE(): Nothing = raiseError(ObjNullPointerError(this))
+
+    fun raiseError(message: String): Nothing {
+        throw ExecutionError(ObjError(this, message))
+    }
+
+    fun raiseError(obj: ObjError): Nothing {
+        throw ExecutionError(obj)
+    }
 
     private val objects = mutableMapOf<String, StoredObj>()
 
@@ -11,14 +29,20 @@ class Context(
         objects[name]
             ?: parent?.get(name)
 
-    fun copy(args: Arguments = Arguments.EMPTY): Context = Context(this, args)
+    fun copy(pos: Pos, args: Arguments = Arguments.EMPTY): Context = Context(this, args, pos)
 
     fun addItem(name: String, isMutable: Boolean, value: Obj?) {
         objects.put(name, StoredObj(name, value, isMutable))
     }
 
     fun getOrCreateNamespace(name: String) =
-        (objects.getOrPut(name) { StoredObj(name, ObjNamespace(name,copy()), isMutable = false) }.value as ObjNamespace)
+        (objects.getOrPut(name) {
+            StoredObj(
+                name,
+                ObjNamespace(name, copy(pos)),
+                isMutable = false
+            )
+        }.value as ObjNamespace)
             .context
 
     inline fun <reified T> addFn(vararg names: String, crossinline fn: suspend Context.() -> T) {
@@ -43,7 +67,7 @@ class Context(
         }
     }
 
-    inline fun <reified T> addConst(value: T,vararg names: String) {
+    inline fun <reified T> addConst(value: T, vararg names: String) {
         val obj = Obj.from(value)
         for (name in names) {
             addItem(
@@ -59,8 +83,5 @@ class Context(
 
     fun containsLocal(name: String): Boolean = name in objects
 
-    companion object {
-        operator fun invoke() = Context()
-    }
 
 }
diff --git a/library/src/commonMain/kotlin/net/sergeych/ling/Obj.kt b/library/src/commonMain/kotlin/net/sergeych/ling/Obj.kt
index b01f90e..d9c8a74 100644
--- a/library/src/commonMain/kotlin/net/sergeych/ling/Obj.kt
+++ b/library/src/commonMain/kotlin/net/sergeych/ling/Obj.kt
@@ -27,7 +27,7 @@ sealed class ClassDef(
     ) {
         instanceLock.withLock {
             instanceMethods[name]?.let {
-                if( !it.isMutable )
+                if (!it.isMutable)
                     throw ScriptError(pos, "existing method $name is frozen and can't be updated")
                 it.value = body
             } ?: instanceMethods.put(name, Item(body, freeze))
@@ -36,7 +36,7 @@ sealed class ClassDef(
 
     //suspend fun callInstanceMethod(context: Context, self: Obj,args: Arguments): Obj {
 //
-  //  }
+    //  }
 }
 
 object ObjClassDef : ClassDef("Obj")
@@ -49,6 +49,18 @@ sealed class Obj : Comparable<Obj> {
 
     open val definition: ClassDef = ObjClassDef
 
+    open fun plus(context: Context, other: Obj): Obj {
+        context.raiseNotImplemented()
+    }
+
+    open fun getAndIncrement(context: Context): Obj {
+        context.raiseNotImplemented()
+    }
+
+    open fun getAndDecrement(context: Context): Obj {
+        context.raiseNotImplemented()
+    }
+
     @Suppress("unused")
     enum class Type {
         @SerialName("Void")
@@ -179,12 +191,27 @@ data class ObjReal(val value: Double) : Obj(), Numeric {
 
 @Serializable
 @SerialName("int")
-data class ObjInt(val value: Long) : Obj(), Numeric {
-    override val asStr by lazy { ObjString(value.toString()) }
-    override val longValue: Long by lazy { value }
-    override val doubleValue: Double by lazy { value.toDouble() }
-    override val toObjInt: ObjInt by lazy { ObjInt(value) }
-    override val toObjReal: ObjReal by lazy { ObjReal(doubleValue) }
+data class ObjInt(var value: Long) : Obj(), Numeric {
+    override val asStr get() = ObjString(value.toString())
+    override val longValue get() = value
+    override val doubleValue get() = value.toDouble()
+    override val toObjInt get() = this
+    override val toObjReal = ObjReal(doubleValue)
+
+    override fun getAndIncrement(context: Context): Obj {
+        return ObjInt(value).also { value++ }
+    }
+
+    override fun getAndDecrement(context: Context): Obj {
+        return ObjInt(value).also { value-- }
+    }
+
+//    override fun plus(context: Context, other: Obj): Obj {
+//        if (other !is Numeric)
+//            context.raiseError("cannot add $this with $other")
+//        return if (other is ObjInt)
+//
+//    }
 
     override fun compareTo(other: Obj): Int {
         if (other !is Numeric) throw IllegalArgumentException("cannot compare $this with $other")
@@ -215,4 +242,13 @@ data class ObjNamespace(val name: String, val context: Context) : Obj() {
     override fun compareTo(other: Obj): Int {
         throw IllegalArgumentException("cannot compare namespaces")
     }
-}
\ No newline at end of file
+}
+
+open class ObjError(val context: Context, val message: String) : Obj() {
+    override val asStr: ObjString by lazy { ObjString("Error: $message") }
+    override fun compareTo(other: Obj): Int {
+        if (other === this) return 0 else return -1
+    }
+}
+
+class ObjNullPointerError(context: Context) : ObjError(context, "object is null")
diff --git a/library/src/commonMain/kotlin/net/sergeych/ling/Parser.kt b/library/src/commonMain/kotlin/net/sergeych/ling/Parser.kt
index a7a4b4c..c7c0752 100644
--- a/library/src/commonMain/kotlin/net/sergeych/ling/Parser.kt
+++ b/library/src/commonMain/kotlin/net/sergeych/ling/Parser.kt
@@ -50,8 +50,21 @@ private class Parser(fromPos: Pos) {
                     Token("=", from, Token.Type.ASSIGN)
             }
 
-            '+' -> Token("+", from, Token.Type.PLUS)
-            '-' -> Token("-", from, Token.Type.MINUS)
+            '+' -> {
+                if( currentChar == '+') {
+                    advance()
+                    Token("+", from, Token.Type.PLUS2)
+                }
+                else
+                    Token("+", from, Token.Type.PLUS)
+            }
+            '-' -> {
+                if (currentChar == '-') {
+                    advance()
+                    Token("--", from, Token.Type.MINUS2)
+                } else
+                    Token("-", from, Token.Type.MINUS)
+            }
             '*' -> Token("*", from, Token.Type.STAR)
             '/' -> {
                 if( currentChar == '/') {
diff --git a/library/src/commonMain/kotlin/net/sergeych/ling/Script.kt b/library/src/commonMain/kotlin/net/sergeych/ling/Script.kt
index 0cee68d..0921a6f 100644
--- a/library/src/commonMain/kotlin/net/sergeych/ling/Script.kt
+++ b/library/src/commonMain/kotlin/net/sergeych/ling/Script.kt
@@ -15,10 +15,10 @@ class Script(
         return lastResult
     }
 
-    suspend fun execute() = execute(defaultContext.copy())
+    suspend fun execute() = execute(defaultContext.copy(pos))
 
     companion object {
-        val defaultContext: Context = Context(null).apply {
+        val defaultContext: Context = Context().apply {
             addFn("println") {
                 print("yn: ")
                 for( (i,a) in args.withIndex() ) {
diff --git a/library/src/commonMain/kotlin/net/sergeych/ling/ScriptError.kt b/library/src/commonMain/kotlin/net/sergeych/ling/ScriptError.kt
index a3bba71..6d17d8d 100644
--- a/library/src/commonMain/kotlin/net/sergeych/ling/ScriptError.kt
+++ b/library/src/commonMain/kotlin/net/sergeych/ling/ScriptError.kt
@@ -1,9 +1,13 @@
+@file:Suppress("CanBeParameter")
+
 package net.sergeych.ling
 
-class ScriptError(val pos: Pos, val errorMessage: String) : Exception(
+open class ScriptError(val pos: Pos, val errorMessage: String) : Exception(
     """
         $pos: Error: $errorMessage
         ${pos.currentLine}
         ${"-".repeat(pos.column)}^
     """.trimIndent()
 )
+
+class ExecutionError(val errorObject: ObjError) : ScriptError(errorObject.context.pos, errorObject.message)
diff --git a/library/src/commonMain/kotlin/net/sergeych/ling/Token.kt b/library/src/commonMain/kotlin/net/sergeych/ling/Token.kt
index 7acbfa7..bcf86b0 100644
--- a/library/src/commonMain/kotlin/net/sergeych/ling/Token.kt
+++ b/library/src/commonMain/kotlin/net/sergeych/ling/Token.kt
@@ -8,6 +8,7 @@ data class Token(val value: String, val pos: Pos, val type: Type) {
         ID, INT, REAL, HEX, STRING, LPAREN, RPAREN, LBRACE, RBRACE, LBRACKET, RBRACKET, COMMA,
         SEMICOLON, COLON,
         PLUS, MINUS, STAR, SLASH, ASSIGN,
+        PLUS2, MINUS2,
         EQ, NEQ, LT, LTE, GT, GTE,
         AND, BITAND, OR, BITOR, NOT, DOT, ARROW, QUESTION, COLONCOLON, PERCENT,
         SINLGE_LINE_COMMENT, MULTILINE_COMMENT,
diff --git a/library/src/commonTest/kotlin/ScriptTest.kt b/library/src/commonTest/kotlin/ScriptTest.kt
index 30570f8..265ca24 100644
--- a/library/src/commonTest/kotlin/ScriptTest.kt
+++ b/library/src/commonTest/kotlin/ScriptTest.kt
@@ -117,7 +117,7 @@ class ScriptTest {
 
     @Test
     fun varsAndConstsTest() = runTest {
-        val context = Context()
+        val context = Context(pos = Pos.builtIn)
         assertEquals(
             ObjVoid, context.eval(
                 """
@@ -137,7 +137,7 @@ class ScriptTest {
 
     @Test
     fun functionTest() = runTest {
-        val context = Context()
+        val context = Context(pos = Pos.builtIn)
         context.eval(
             """
             fun foo(a, b) {
@@ -163,7 +163,7 @@ class ScriptTest {
 
     @Test
     fun simpleClosureTest() = runTest {
-        val context = Context()
+        val context = Context(pos = Pos.builtIn)
         context.eval(
             """
             var global = 10
@@ -180,7 +180,7 @@ class ScriptTest {
 
     @Test
     fun nullAndVoidTest() = runTest {
-        val context = Context()
+        val context = Context(pos = Pos.builtIn)
         assertEquals(ObjVoid, context.eval("void"))
         assertEquals(ObjNull, context.eval("null"))
     }
@@ -252,7 +252,7 @@ class ScriptTest {
     @Test
     fun ifTest() = runTest {
         // if - single line
-        var context = Context()
+        var context = Context(pos = Pos.builtIn)
         context.eval(
             """
             fn test1(n) {
@@ -267,7 +267,7 @@ class ScriptTest {
         assertEquals("more", context.eval("test1(1)").toString())
 
         // if - multiline (block)
-        context = Context()
+        context = Context(pos = Pos.builtIn)
         context.eval(
             """
             fn test1(n) {
@@ -286,7 +286,7 @@ class ScriptTest {
         assertEquals("answer: more", context.eval("test1(1)").toString())
 
         // else single line1
-        context = Context()
+        context = Context(pos = Pos.builtIn)
         context.eval(
             """
             fn test1(n) {
@@ -301,7 +301,7 @@ class ScriptTest {
         assertEquals("more", context.eval("test1(1)").toString())
 
         // if/else with blocks
-        context = Context()
+        context = Context(pos = Pos.builtIn )
         context.eval(
             """
             fn test1(n) {
@@ -443,4 +443,86 @@ class ScriptTest {
                 .toString()
         )
     }
+
+    @Test
+    fun testIncr() = runTest {
+        val c = Context()
+        c.eval("var x = 10")
+        assertEquals(10, c.eval("x++").toInt())
+        assertEquals(11, c.eval("x++").toInt())
+        assertEquals(12, c.eval("x").toInt())
+
+        assertEquals(12, c.eval("x").toInt())
+        assertEquals(12, c.eval("x").toInt())
+    }
+
+    @Test
+    fun testDecr() = runTest {
+        val c = Context()
+        c.eval("var x = 9")
+        assertEquals(9, c.eval("x--").toInt())
+        assertEquals(8, c.eval("x--").toInt())
+        assertEquals(7, c.eval("x--").toInt())
+        assertEquals(6, c.eval("x--").toInt())
+        assertEquals(5, c.eval("x").toInt())
+    }
+
+    @Test
+    fun testDecrIncr() = runTest {
+        val c = Context()
+        c.eval("var x = 9")
+        assertEquals(9, c.eval("x++").toInt())
+        assertEquals(10, c.eval("x++").toInt())
+        assertEquals(11, c.eval("x").toInt())
+        assertEquals(11, c.eval("x--").toInt())
+        assertEquals(10, c.eval("x--").toInt())
+        assertEquals(9, c.eval("x--").toInt())
+        assertEquals(8, c.eval("x--").toInt())
+        assertEquals(7, c.eval("x + 0").toInt())
+    }
+
+    @Test
+    fun testDecrIncr2() = runTest {
+        val c = Context()
+        c.eval("var x = 9")
+        assertEquals(9, c.eval("x--").toInt())
+        assertEquals(8, c.eval("x--").toInt())
+        assertEquals(7, c.eval("x--").toInt())
+        assertEquals(6, c.eval("x").toInt())
+        assertEquals(6, c.eval("x++").toInt())
+        assertEquals(7, c.eval("x++").toInt())
+        assertEquals(8, c.eval("x")
+            .also {
+                println("${it.toDouble()} ${it.toInt()} ${it.toLong()} ${it.toInt()}")
+            }
+            .toInt())
+    }
+
+    @Test
+    fun testDecrIncr3() = runTest {
+        val c = Context()
+        c.eval("var x = 9")
+        assertEquals(9, c.eval("x++").toInt())
+        assertEquals(10, c.eval("x++").toInt())
+        assertEquals(11, c.eval("x++").toInt())
+        assertEquals(12, c.eval("x").toInt())
+        assertEquals(12, c.eval("x--").toInt())
+        assertEquals(11, c.eval("x").toInt())
+    }
+
+    @Test
+    fun testIncrAndDecr() = runTest {
+        val c = Context()
+        assertEquals( "8", c.eval("""
+            var x = 5
+            x-- 
+            x-- 
+            x++ 
+            x * 2
+        """).toString())
+
+        assertEquals( "4", c.eval("x").toString())
+//        assertEquals( "8", c.eval("x*2").toString())
+//        assertEquals( "4", c.eval("x+0").toString())
+    }
 }
\ No newline at end of file