diff --git a/libraries/tools/idl2k/src/main/kotlin/gen.kt b/libraries/tools/idl2k/src/main/kotlin/gen.kt
index 998be95aa23..99b6ea8f456 100644
--- a/libraries/tools/idl2k/src/main/kotlin/gen.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/gen.kt
@@ -1,6 +1,6 @@
 package org.jetbrains.idl2k
 
-import java.util.HashSet
+import java.util.*
 
 private fun Operation.getterOrSetter() = this.attributes.map { it.call }.toSet().let { attributes ->
     when {
@@ -17,6 +17,17 @@ fun String.ensureNullable() = when {
     else -> "$this?"
 }
 
+fun String.dropNullable() = when {
+    endsWith(")?") -> this.removeSuffix("?").removeSurrounding("(", ")")
+    endsWith("?") -> this.removeSuffix("?")
+    else -> this
+}
+
+fun String.copyNullabilityFrom(type : String) = when {
+    type.endsWith("?") -> ensureNullable()
+    else -> this
+}
+
 fun generateFunction(repository: Repository, function: Operation, functionName: String, nativeGetterOrSetter: NativeGetterOrSetter = function.getterOrSetter()): GenerateFunction =
         function.attributes.map { it.call }.toSet().let { attributes ->
             GenerateFunction(
@@ -44,8 +55,26 @@ fun generateFunctions(repository: Repository, function: Operation): List<Generat
         NativeGetterOrSetter.GETTER -> generateFunction(repository, function, "get")
         NativeGetterOrSetter.SETTER -> generateFunction(repository, function, "set")
     }
+    val callbackArgumentsAsLambdas = function.parameters.map {
+        val interfaceType = repository.interfaces[it.type.dropNullable()]
+        when {
+            interfaceType == null -> it
+            interfaceType.callback -> interfaceType.operations.single().let { callbackFunction ->
+                it.copy(type = callbackFunction.parameters
+                        .map { mapType(repository, it.type) }
+                        .join(",", "(", ") -> ${mapType(repository, callbackFunction.returnType)}")
+                        .copyNullabilityFrom(it.type))
+            }
+            else -> it
+        }
+    }
 
-    return listOf(realFunction, getterOrSetterFunction).filterNotNull()
+    val functionWithCallbackOrNull = when {
+        callbackArgumentsAsLambdas == function.parameters -> null
+        else -> generateFunction(repository, function.copy(parameters = callbackArgumentsAsLambdas), function.name, NativeGetterOrSetter.NONE)
+    }
+
+    return listOf(realFunction, getterOrSetterFunction, functionWithCallbackOrNull).filterNotNull()
 }
 
 fun generateAttribute(putNoImpl: Boolean, repository: Repository, attribute: Attribute): GenerateAttribute =
diff --git a/libraries/tools/idl2k/src/main/kotlin/idl.kt b/libraries/tools/idl2k/src/main/kotlin/idl.kt
index b49cb96f6b2..d513b5b12d6 100644
--- a/libraries/tools/idl2k/src/main/kotlin/idl.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/idl.kt
@@ -16,24 +16,20 @@
 
 package org.jetbrains.idl2k
 
-import org.antlr.v4.runtime.*
-import org.antlr.webidl.WebIDLBaseListener
+import org.antlr.v4.runtime.CharStream
+import org.antlr.v4.runtime.CommonTokenStream
+import org.antlr.v4.runtime.ParserRuleContext
+import org.antlr.v4.runtime.tree.TerminalNode
+import org.antlr.webidl.WebIDLBaseVisitor
 import org.antlr.webidl.WebIDLLexer
 import org.antlr.webidl.WebIDLParser
 import org.antlr.webidl.WebIDLParser.*
-import org.antlr.v4.runtime.tree.TerminalNode
-import org.antlr.webidl.WebIDLBaseVisitor
-import org.jsoup.Jsoup
-import java.io.File
-import java.io.Reader
-import java.io.StringReader
-import java.net.URL
-import java.util.*
+import java.util.ArrayList
 
-data class ExtendedAttribute(val name : String?, val call : String, val arguments : List<Attribute>)
-data class Operation(val name : String, val returnType : String, val parameters : List<Attribute>, val attributes : List<ExtendedAttribute>)
-data class Attribute(val name : String, val type : String, val readOnly : Boolean, val defaultValue : String? = null, val vararg : Boolean)
-data class Constant(val name : String, val type : String, val value : String?)
+data class ExtendedAttribute(val name: String?, val call: String, val arguments: List<Attribute>)
+data class Operation(val name: String, val returnType: String, val parameters: List<Attribute>, val attributes: List<ExtendedAttribute>)
+data class Attribute(val name: String, val type: String, val readOnly: Boolean, val defaultValue: String? = null, val vararg: Boolean)
+data class Constant(val name: String, val type: String, val value: String?)
 
 enum class DefinitionType {
     INTERFACE
@@ -42,11 +38,24 @@ enum class DefinitionType {
     ENUM
     DICTIONARY
 }
+
 trait Definition
-data class TypedefDefinition(val types: String, val namespace : String, val name: String) : Definition
-data class InterfaceDefinition(val name : String, val namespace : String, val extendedAttributes: List<ExtendedAttribute>, val operations : List<Operation>, val attributes : List<Attribute>, val superTypes : List<String>, val constants : List<Constant>, val dictionary : Boolean = false) : Definition
-data class ExtensionInterfaceDefinition(val namespace : String, val name : String, val implements : String) : Definition
-data class EnumDefinition(val namespace : String, val name : String) : Definition
+data class TypedefDefinition(val types: String, val namespace: String, val name: String) : Definition
+data class InterfaceDefinition(
+        val name: String,
+        val namespace: String,
+        val extendedAttributes: List<ExtendedAttribute>,
+        val operations: List<Operation>,
+        val attributes: List<Attribute>,
+        val superTypes: List<String>,
+        val constants: List<Constant>,
+        val dictionary: Boolean = false,
+        val partial: Boolean,
+        val callback: Boolean
+) : Definition
+
+data class ExtensionInterfaceDefinition(val namespace: String, val name: String, val implements: String) : Definition
+data class EnumDefinition(val namespace: String, val name: String) : Definition
 
 class ExtendedAttributeArgumentsParser : WebIDLBaseVisitor<List<Attribute>>() {
     private val arguments = ArrayList<Attribute>()
@@ -66,14 +75,14 @@ class ExtendedAttributeArgumentsParser : WebIDLBaseVisitor<List<Attribute>>() {
 }
 
 class ExtendedAttributeParser : WebIDLBaseVisitor<ExtendedAttribute>() {
-    private var name : String? = null
-    private var call : String = ""
+    private var name: String? = null
+    private var call: String = ""
     private val arguments = ArrayList<Attribute>()
 
     override fun defaultResult(): ExtendedAttribute = ExtendedAttribute(name, call, arguments)
 
     override fun visitExtendedAttribute(ctx: WebIDLParser.ExtendedAttributeContext): ExtendedAttribute {
-        call = ctx.children?.filter {it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL}?.firstOrNull()?.getText() ?: ""
+        call = ctx.children?.filter { it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL }?.firstOrNull()?.getText() ?: ""
 
         visitChildren(ctx)
         return defaultResult()
@@ -84,9 +93,9 @@ class ExtendedAttributeParser : WebIDLBaseVisitor<ExtendedAttribute>() {
         return defaultResult()
     }
 
-    override fun visitIdentifierList(ctx : IdentifierListContext) : ExtendedAttribute {
+    override fun visitIdentifierList(ctx: IdentifierListContext): ExtendedAttribute {
         object : WebIDLBaseVisitor<Unit>() {
-            override fun visitTerminal(node : TerminalNode) {
+            override fun visitTerminal(node: TerminalNode) {
                 if (node.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL) {
                     arguments.add(Attribute(node.getText(), "any", true, vararg = false))
                 }
@@ -140,9 +149,9 @@ class TypeVisitor : WebIDLBaseVisitor<String>() {
     }
 }
 
-class OperationVisitor(val attributes : List<ExtendedAttribute>) : WebIDLBaseVisitor<Operation>() {
-    private var name : String = ""
-    private var returnType : String = ""
+class OperationVisitor(val attributes: List<ExtendedAttribute>) : WebIDLBaseVisitor<Operation>() {
+    private var name: String = ""
+    private var returnType: String = ""
     private val parameters = ArrayList<Attribute>()
     private val exts = ArrayList<ExtendedAttribute>()
 
@@ -177,13 +186,13 @@ class OperationVisitor(val attributes : List<ExtendedAttribute>) : WebIDLBaseVis
     }
 }
 
-class AttributeVisitor(val readOnly : Boolean) : WebIDLBaseVisitor<Attribute>() {
-    var type : String = ""
-    var name : String = ""
-    var defaultValue : String? = null
-    var vararg : Boolean = false
+class AttributeVisitor(val readOnly: Boolean) : WebIDLBaseVisitor<Attribute>() {
+    var type: String = ""
+    var name: String = ""
+    var defaultValue: String? = null
+    var vararg: Boolean = false
 
-    override fun defaultResult() : Attribute = Attribute(name, type, readOnly, defaultValue, vararg)
+    override fun defaultResult(): Attribute = Attribute(name, type, readOnly, defaultValue, vararg)
 
     override fun visitType(ctx: WebIDLParser.TypeContext): Attribute {
         type = TypeVisitor().visit(ctx)
@@ -191,7 +200,7 @@ class AttributeVisitor(val readOnly : Boolean) : WebIDLBaseVisitor<Attribute>()
     }
 
     override fun visitOptionalOrRequiredArgument(ctx: WebIDLParser.OptionalOrRequiredArgumentContext): Attribute {
-        if (ctx.children?.any {it is TerminalNode && it.getText() == "optional"} ?: false) {
+        if (ctx.children?.any { it is TerminalNode && it.getText() == "optional" } ?: false) {
             defaultValue = "noImpl"
         }
         return visitChildren(ctx)
@@ -200,8 +209,8 @@ class AttributeVisitor(val readOnly : Boolean) : WebIDLBaseVisitor<Attribute>()
     override fun visitAttributeRest(ctx: WebIDLParser.AttributeRestContext): Attribute {
         try {
             name = getName(ctx)
-        } catch (ignore : Throwable) {
-            name = ctx.children.filter { it is TerminalNode}.filter {it.getText() != ";"}.last().getText()
+        } catch (ignore: Throwable) {
+            name = ctx.children.filter { it is TerminalNode }.filter { it.getText() != ";" }.last().getText()
         }
         return defaultResult()
     }
@@ -209,7 +218,7 @@ class AttributeVisitor(val readOnly : Boolean) : WebIDLBaseVisitor<Attribute>()
     override fun visitArgumentName(ctx: WebIDLParser.ArgumentNameContext): Attribute {
         try {
             name = getName(ctx)
-        } catch (ignore : Throwable) {
+        } catch (ignore: Throwable) {
             name = ctx.getText()
         }
         return defaultResult()
@@ -226,12 +235,12 @@ class AttributeVisitor(val readOnly : Boolean) : WebIDLBaseVisitor<Attribute>()
     }
 }
 
-class ConstantVisitor(val attributes : List<ExtendedAttribute>) : WebIDLBaseVisitor<Constant>() {
-    var type : String = ""
-    var name : String = ""
-    var value : String? = null
+class ConstantVisitor(val attributes: List<ExtendedAttribute>) : WebIDLBaseVisitor<Constant>() {
+    var type: String = ""
+    var name: String = ""
+    var value: String? = null
 
-    override fun defaultResult() : Constant = Constant(name, type, value)
+    override fun defaultResult(): Constant = Constant(name, type, value)
 
     override fun visitConst_(ctx: WebIDLParser.Const_Context): Constant {
         name = getName(ctx)
@@ -250,27 +259,43 @@ class ConstantVisitor(val attributes : List<ExtendedAttribute>) : WebIDLBaseVisi
     }
 }
 
-class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val namespace : String) : WebIDLBaseVisitor<Definition>() {
-    private var type : DefinitionType = DefinitionType.INTERFACE
+class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val namespace: String) : WebIDLBaseVisitor<Definition>() {
+    private var type: DefinitionType = DefinitionType.INTERFACE
     private var name = ""
     private val memberAttributes = ArrayList<ExtendedAttribute>()
     private val operations = ArrayList<Operation>()
     private val attributes = ArrayList<Attribute>()
-    private var readOnly : Boolean = false
+    private var readOnly: Boolean = false
     private val inherited = ArrayList<String>()
     private var typedefType: String? = null
-    private var implements : String? = null
+    private var implements: String? = null
     private val constants = ArrayList<Constant>()
+    private var partial = false
+    private var callback = false
 
-    override fun defaultResult(): Definition = when(type) {
-        DefinitionType.INTERFACE -> InterfaceDefinition(name, namespace, extendedAttributes, operations, attributes, inherited, constants)
-        DefinitionType.DICTIONARY -> InterfaceDefinition(name, namespace, extendedAttributes, operations, attributes, inherited, constants, true)
+    override fun defaultResult(): Definition = when (type) {
+        DefinitionType.INTERFACE -> InterfaceDefinition(name, namespace, extendedAttributes, operations, attributes, inherited, constants, false, partial, callback)
+        DefinitionType.DICTIONARY -> InterfaceDefinition(name, namespace, extendedAttributes, operations, attributes, inherited, constants, true, partial, callback)
         DefinitionType.EXTENSION_INTERFACE -> ExtensionInterfaceDefinition(namespace, name, implements ?: "")
         DefinitionType.TYPEDEF -> TypedefDefinition(typedefType ?: "", namespace, name)
         DefinitionType.ENUM -> EnumDefinition(namespace, name)
     }
 
-    override fun visitInterface_(ctx: Interface_Context) : Definition {
+    override fun visitCallbackRestOrInterface(ctx: WebIDLParser.CallbackRestOrInterfaceContext): Definition {
+        callback = true
+        return visitChildren(ctx)
+    }
+
+    override fun visitCallbackRest(ctx: WebIDLParser.CallbackRestContext): Definition {
+        name = getName(ctx)
+        with(OperationVisitor(memberAttributes.toList())) {
+            operations.add(visit(ctx))
+        }
+        memberAttributes.clear()
+        return defaultResult()
+    }
+
+    override fun visitInterface_(ctx: Interface_Context): Definition {
         name = getName(ctx)
         visitChildren(ctx)
         return defaultResult()
@@ -278,12 +303,14 @@ class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val nam
 
     override fun visitPartialInterface(ctx: WebIDLParser.PartialInterfaceContext): Definition {
         name = getName(ctx)
+        partial = true
         visitChildren(ctx)
         return defaultResult()
     }
 
     override fun visitTypedef(ctx: WebIDLParser.TypedefContext): Definition {
-        if (name != "") { // TODO temporary workaround for local typedefs
+        if (name != "") {
+            // TODO temporary workaround for local typedefs
             return defaultResult()
         }
 
@@ -293,7 +320,7 @@ class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val nam
         typedefType = ctx.accept(object : WebIDLBaseVisitor<String>() {
             private var foundType = ""
 
-            override fun defaultResult() : String = foundType
+            override fun defaultResult(): String = foundType
 
             override fun visitType(ctx: WebIDLParser.TypeContext): String {
                 foundType = TypeVisitor().visit(ctx)
@@ -320,17 +347,17 @@ class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val nam
 
     override fun visitDictionaryMember(ctx: DictionaryMemberContext): Definition {
         val name = ctx.children
-                ?.filter {it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL}
+                ?.filter { it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL }
                 ?.first { it.getText() != "" }
                 ?.getText()
 
-        val type = TypeVisitor().visit(ctx.children.first {it is TypeContext})
+        val type = TypeVisitor().visit(ctx.children.first { it is TypeContext })
         val defaultValue = object : WebIDLBaseVisitor<String?>() {
-            private var value : String? = null
+            private var value: String? = null
 
             override fun defaultResult() = value
 
-            override fun visitDefaultValue(ctx2: DefaultValueContext) : String? {
+            override fun visitDefaultValue(ctx2: DefaultValueContext): String? {
                 value = ctx2.getText()
                 return value
             }
@@ -342,7 +369,7 @@ class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val nam
     }
 
     override fun visitImplementsStatement(ctx: ImplementsStatementContext): Definition {
-        val identifiers = ctx.children.filter {it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL}.map {it.getText()}
+        val identifiers = ctx.children.filter { it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL }.map { it.getText() }
 
         if (identifiers.size() >= 2) {
             type = DefinitionType.EXTENSION_INTERFACE
@@ -354,7 +381,7 @@ class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val nam
         return defaultResult()
     }
 
-    override fun visitOperation(ctx: OperationContext) : Definition {
+    override fun visitOperation(ctx: OperationContext): Definition {
         with(OperationVisitor(memberAttributes.toList())) {
             operations.add(visit(ctx))
         }
@@ -393,7 +420,7 @@ class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val nam
         return defaultResult()
     }
 
-    override fun visitExtendedAttribute(ctx: ExtendedAttributeContext) : Definition {
+    override fun visitExtendedAttribute(ctx: ExtendedAttributeContext): Definition {
         val att = with(ExtendedAttributeParser()) {
             visit(ctx)
         }
@@ -404,9 +431,9 @@ class DefinitionVisitor(val extendedAttributes: List<ExtendedAttribute>, val nam
 
 }
 
-private fun getName(ctx: ParserRuleContext) = ctx.children.first {it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL}.getText()
+private fun getName(ctx: ParserRuleContext) = ctx.children.first { it is TerminalNode && it.getSymbol().getType() == WebIDLLexer.IDENTIFIER_WEBIDL }.getText()
 
-fun parseIDL(reader : CharStream) : Repository {
+fun parseIDL(reader: CharStream): Repository {
     val ll = WebIDLLexer(reader)
     val pp = WebIDLParser(CommonTokenStream(ll))
 
@@ -438,24 +465,27 @@ fun parseIDL(reader : CharStream) : Repository {
     })
 
     return Repository(
-            declarations.filterIsInstance<InterfaceDefinition>().filter {it.name.isEmpty().not()}.groupBy { it.name }.mapValues { it.getValue().reduce(::merge) },
+            declarations.filterIsInstance<InterfaceDefinition>().filter { it.name.isEmpty().not() }.groupBy { it.name }.mapValues { it.getValue().reduce(::merge) },
             declarations.filterIsInstance<TypedefDefinition>().groupBy { it.name }.mapValues { it.getValue().first() },
-            declarations.filterIsInstance<ExtensionInterfaceDefinition>().groupBy { it.name }.mapValues { it.getValue().map {it.implements} },
-            declarations.filterIsInstance<EnumDefinition>().groupBy { it.name }.mapValues { it.getValue().reduce {a, b -> a} }
+            declarations.filterIsInstance<ExtensionInterfaceDefinition>().groupBy { it.name }.mapValues { it.getValue().map { it.implements } },
+            declarations.filterIsInstance<EnumDefinition>().groupBy { it.name }.mapValues { it.getValue().reduce { a, b -> a } }
     )
 }
 
-fun merge(i1 : InterfaceDefinition, i2 : InterfaceDefinition) : InterfaceDefinition {
+fun merge(i1: InterfaceDefinition, i2: InterfaceDefinition): InterfaceDefinition {
     require(i1.name == i2.name)
 
-    return InterfaceDefinition(i1.name, i1.namespace,
+    return InterfaceDefinition(i1.name,
+            namespace = if (i1.partial) i2.namespace else i1.namespace,
             extendedAttributes = i1.extendedAttributes merge i2.extendedAttributes,
             operations = i1.operations merge i2.operations,
             attributes = i1.attributes merge i2.attributes,
             superTypes = i1.superTypes merge i2.superTypes,
             constants = i1.constants merge i2.constants,
-            dictionary = i1.dictionary || i2.dictionary
-            )
+            dictionary = i1.dictionary || i2.dictionary,
+            partial = i1.partial && i2.partial,
+            callback = i1.callback && i2.callback
+    )
 }
 
-fun <T> List<T>.merge(other : List<T>) = (this + other).distinct().toList()
+fun <T> List<T>.merge(other: List<T>) = (this + other).distinct().toList()
diff --git a/libraries/tools/idl2k/src/main/kotlin/main.kt b/libraries/tools/idl2k/src/main/kotlin/main.kt
index 2a88a749aa3..5ad6f7b7c4d 100644
--- a/libraries/tools/idl2k/src/main/kotlin/main.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/main.kt
@@ -20,7 +20,7 @@ fun main(args: Array<String>) {
         val fileRepository = parseIDL(ANTLRFileStream(e.getAbsolutePath(), "UTF-8"))
 
         Repository(
-                interfaces = acc.interfaces + fileRepository.interfaces,
+                interfaces = acc.interfaces.mergeReduce(fileRepository.interfaces, ::merge),
                 typeDefs = acc.typeDefs + fileRepository.typeDefs,
                 externals = acc.externals merge fileRepository.externals,
                 enums = acc.enums + fileRepository.enums
@@ -53,6 +53,24 @@ fun main(args: Array<String>) {
     }
 }
 
+private fun <K, V> Map<K, List<V>>.reduceValues(reduce : (V, V) -> V = {a, b -> b}) : Map<K, V> = mapValues { it.value.reduce(reduce) }
+
+private fun <K, V> Map<K, V>.mergeReduce(other : Map<K, V>, reduce : (V, V) -> V = {a, b -> b}) : Map<K, V> {
+    val result = LinkedHashMap<K, V>(this.size() + other.size())
+    result.putAll(this)
+    other.forEach { e ->
+        val existing = result[e.key]
+
+        if (existing == null) {
+            result[e.key] = e.value
+        } else {
+            result[e.key] = reduce(e.value, existing)
+        }
+    }
+
+    return result
+}
+
 private fun <K, V> Map<K, List<V>>.merge(other : Map<K, List<V>>) : Map<K, List<V>> {
     val result = LinkedHashMap<K, MutableList<V>>(size() + other.size())
     this.forEach {
diff --git a/libraries/tools/idl2k/src/main/kotlin/model.kt b/libraries/tools/idl2k/src/main/kotlin/model.kt
index 1e771703ed9..5785706e5db 100644
--- a/libraries/tools/idl2k/src/main/kotlin/model.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/model.kt
@@ -34,8 +34,12 @@ val GenerateAttribute.getterNoImpl: Boolean
 val GenerateAttribute.setterNoImpl: Boolean
     get() = getterSetterNoImpl && !readOnly
 
+val String.typeSignature: String
+    get() = if (contains("->")) "()" else this
+
 val GenerateAttribute.signature: String
-    get() = "$name:$type"
+    get() = "$name:${type.typeSignature}"
+fun GenerateAttribute.dynamicIfUnknownType(allTypes : Set<String>, standardTypes : Set<String> = standardTypes()) = this.copy(type = type.dynamicIfUnknownType(allTypes, standardTypes))
 
 enum class NativeGetterOrSetter {
     NONE
@@ -86,8 +90,11 @@ data class GenerateTraitOrClass(
 
 
 val GenerateFunction.signature: String
-    get() = arguments.map { it.type }.joinToString(", ", "$name(", ")")
+    get() = arguments.map { it.type.typeSignature }.joinToString(", ", "$name(", ")")
 
+fun GenerateFunction.dynamicIfUnknownType(allTypes : Set<String>) = standardTypes().let { standardTypes ->
+    this.copy(returnType = returnType.dynamicIfUnknownType(allTypes, standardTypes), arguments = arguments.map { it.dynamicIfUnknownType(allTypes, standardTypes) })
+}
 
 fun InterfaceDefinition.findExtendedAttribute(name: String) = extendedAttributes.firstOrNull { it.call == name }
 fun InterfaceDefinition?.hasExtendedAttribute(name: String) = this?.findExtendedAttribute(name) ?: null != null
diff --git a/libraries/tools/idl2k/src/main/kotlin/render.kt b/libraries/tools/idl2k/src/main/kotlin/render.kt
index 34dd86a34cd..de33aedcc0b 100644
--- a/libraries/tools/idl2k/src/main/kotlin/render.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/render.kt
@@ -2,13 +2,13 @@ package org.jetbrains.idl2k
 
 import java.math.BigInteger
 
-private fun <O: Appendable> O.indent(level : Int) {
+private fun <O : Appendable> O.indent(level: Int) {
     for (i in 1..level) {
         append("    ")
     }
 }
 
-private fun Appendable.renderAttributeDeclaration(allTypes: Set<String>, arg: GenerateAttribute, override: Boolean, level : Int = 1) {
+private fun Appendable.renderAttributeDeclaration(allTypes: Set<String>, arg: GenerateAttribute, override: Boolean, level: Int = 1) {
     indent(level)
 
     if (override) {
@@ -19,7 +19,7 @@ private fun Appendable.renderAttributeDeclaration(allTypes: Set<String>, arg: Ge
     append(" ")
     append(arg.name)
     append(": ")
-    append(arg.type.dynamicIfUnknownType(allTypes))
+    append(arg.type)
     if (arg.initializer != null) {
         append(" = ")
         append(arg.initializer.replaceWrongConstants(arg.type))
@@ -50,7 +50,7 @@ private fun Appendable.renderArgumentsDeclaration(allTypes: Set<String>, args: L
                 }
                 append(it.name.replaceKeywords())
                 append(": ")
-                append(it.type.dynamicIfUnknownType(allTypes))
+                append(it.type)
                 if (!omitDefaults && it.initializer != null && it.initializer != "") {
                     append(" = ")
                     append(it.initializer.replaceWrongConstants(it.type))
@@ -58,7 +58,7 @@ private fun Appendable.renderArgumentsDeclaration(allTypes: Set<String>, args: L
             }
         }.joinTo(this, ", ")
 
-private fun renderCall(call: GenerateFunctionCall) = "${call.name.replaceKeywords()}(${call.arguments.map {it.replaceKeywords()}.join(", ")})"
+private fun renderCall(call: GenerateFunctionCall) = "${call.name.replaceKeywords()}(${call.arguments.map { it.replaceKeywords() }.join(", ")})"
 
 private fun Appendable.renderFunctionDeclaration(allTypes: Set<String>, f: GenerateFunction, override: Boolean) {
     indent(1)
@@ -77,11 +77,11 @@ private fun Appendable.renderFunctionDeclaration(allTypes: Set<String>, f: Gener
     }
     append("fun ${f.name.replaceKeywords()}(")
     renderArgumentsDeclaration(allTypes, f.arguments, override)
-    appendln("): ${f.returnType.dynamicIfUnknownType(allTypes)} = noImpl")
+    appendln("): ${f.returnType} = noImpl")
 }
 
-fun Appendable.render(allTypes: Map<String, GenerateTraitOrClass>, typeNamesToUnions: Map<String, List<String>>, iface: GenerateTraitOrClass, markerAnnotation : Boolean = false) {
-    append("native ")
+fun Appendable.render(allTypes: Map<String, GenerateTraitOrClass>, typeNamesToUnions: Map<String, List<String>>, iface: GenerateTraitOrClass, markerAnnotation: Boolean = false) {
+    append("native public ")
     if (markerAnnotation) {
         append("marker ")
     }
@@ -93,7 +93,7 @@ fun Appendable.render(allTypes: Map<String, GenerateTraitOrClass>, typeNamesToUn
     append(iface.name)
     if (iface.constructor != null && iface.constructor.arguments.isNotEmpty()) {
         append("(")
-        renderArgumentsDeclaration(allTypes.keySet(), iface.constructor.arguments, false)
+        renderArgumentsDeclaration(allTypes.keySet(), iface.constructor.arguments.map { it.dynamicIfUnknownType(allTypes.keySet()) }, false)
         append(")")
     }
 
@@ -116,10 +116,10 @@ fun Appendable.render(allTypes: Map<String, GenerateTraitOrClass>, typeNamesToUn
     val superFunctions = allSuperTypes.flatMap { it.memberFunctions }.distinct()
     val superSignatures = superAttributes.map { it.signature } merge superFunctions.map { it.signature }
 
-    iface.memberAttributes.filter { it !in superAttributes }.forEach { arg ->
+    iface.memberAttributes.filter { it !in superAttributes }.map { it.dynamicIfUnknownType(allTypes.keySet()) }.groupBy { it.signature }.reduceValues().values().forEach { arg ->
         renderAttributeDeclaration(allTypes.keySet(), arg, arg.signature in superSignatures)
     }
-    iface.memberFunctions.filter { it !in superFunctions }.forEach {
+    iface.memberFunctions.filter { it !in superFunctions }.map { it.dynamicIfUnknownType(allTypes.keySet()) }.groupBy { it.signature }.reduceValues(::betterFunction).values().forEach {
         renderFunctionDeclaration(allTypes.keySet(), it, it.signature in superSignatures)
     }
     if (iface.constants.isNotEmpty()) {
@@ -137,27 +137,38 @@ fun Appendable.render(allTypes: Map<String, GenerateTraitOrClass>, typeNamesToUn
     appendln()
 }
 
-fun <K, V> List<Pair<K, V>>.toMultiMap() : Map<K, List<V>> = groupBy { it.first }.mapValues { it.value.map { it.second } }
+fun betterFunction(f1: GenerateFunction, f2: GenerateFunction): GenerateFunction =
+        f1.copy(
+                arguments = f1.arguments
+                        .zip(f2.arguments)
+                        .map { it.first.copy(type = it.map { it.type }.betterType(), name = it.map { it.name }.betterName()) }
+        )
 
-fun Appendable.render(namespace : String, ifaces: List<GenerateTraitOrClass>, typedefs : Iterable<TypedefDefinition>) {
+private fun <F, T> Pair<F, F>.map(block: (F) -> T) = block(first) to block(second)
+private fun Pair<String, String>.betterType() = if (listOf("dynamic", "Any", "Any").any { first.contains(it) }) first else second
+private fun Pair<String, String>.betterName() = if (((0..9).map { it.toString() } + listOf("arg")).none { first.toLowerCase().contains(it) }) first else second
+
+fun <K, V> List<Pair<K, V>>.toMultiMap(): Map<K, List<V>> = groupBy { it.first }.mapValues { it.value.map { it.second } }
+
+fun Appendable.render(namespace: String, ifaces: List<GenerateTraitOrClass>, typedefs: Iterable<TypedefDefinition>) {
     val declaredTypes = ifaces.toMap { it.name }
 
     val anonymousUnionTypes = collectUnionTypes(declaredTypes)
     val anonymousUnionTypeTraits = generateUnionTypeTraits(anonymousUnionTypes)
     val anonymousUnionsMap = anonymousUnionTypeTraits.toMap { it.name }
 
-    val typedefsToBeGenerated = typedefs.filter {it.types.startsWith("Union<")}
-            .filter {it.namespace == namespace}
+    val typedefsToBeGenerated = typedefs.filter { it.types.startsWith("Union<") }
+            .filter { it.namespace == namespace }
             .map { NamedValue(it.name, UnionType(namespace, splitUnionType(it.types))) }
-            .filter { it.value.memberTypes.all { type -> type in declaredTypes} }
+            .filter { it.value.memberTypes.all { type -> type in declaredTypes } }
     val typedefsMarkerTraits = typedefsToBeGenerated.groupBy { it.name }.mapValues { mapUnionType(it.value.first().value).copy(name = it.key) }
 
     // TODO better name, extract duplication
     val typeNamesToUnions = anonymousUnionTypes.flatMap { unionType -> unionType.memberTypes.map { unionMember -> unionMember to unionType.name } }.toMultiMap()
-            typedefsToBeGenerated.flatMap { typedef -> typedef.value.memberTypes.map { unionMember -> unionMember to typedef.name } }.toMultiMap()
+    typedefsToBeGenerated.flatMap { typedef -> typedef.value.memberTypes.map { unionMember -> unionMember to typedef.name } }.toMultiMap()
 
     val allTypes = declaredTypes + anonymousUnionsMap + typedefsMarkerTraits
-    declaredTypes.values().filter {it.namespace == namespace}.forEach {
+    declaredTypes.values().filter { it.namespace == namespace }.forEach {
         render(allTypes, typeNamesToUnions, it)
     }
 
diff --git a/libraries/tools/idl2k/src/main/kotlin/typeMappings.kt b/libraries/tools/idl2k/src/main/kotlin/typeMappings.kt
index b7c9b673e3a..28f9cc5ebee 100644
--- a/libraries/tools/idl2k/src/main/kotlin/typeMappings.kt
+++ b/libraries/tools/idl2k/src/main/kotlin/typeMappings.kt
@@ -28,7 +28,7 @@ private val typeMapper = mapOf(
         "short" to "Short",
         "long" to "Int",
         "double" to "Double",
-        "any" to "Any",
+        "any" to "Any?",
         "DOMTimeStamp" to "Number",
         "object" to "dynamic", // TODO map to Any?
         "EventHandler" to "(Event) -> Unit",
@@ -55,15 +55,24 @@ fun allSuperTypesImpl(roots: List<GenerateTraitOrClass>, all: Map<String, Genera
     }
 }
 
-fun String.dynamicIfUnknownType(allTypes: Set<String>, standardTypes: Set<String> = typeMapper.values().toSet()): String =
-        if (this.endsWith("?")) this.substring(0, length() - 1).dynamicIfUnknownType(allTypes, standardTypes).ensureNullable()
-        else if (this.startsWith("Union<")) UnionType("", splitUnionType(this)).name.dynamicIfUnknownType(allTypes, standardTypes) // TODO check it is required here
-        else if (this in allTypes || this in standardTypes) this else "dynamic"
+fun standardTypes() = typeMapper.values().map {it.dropNullable()}.toSet()
+fun String.dynamicIfUnknownType(allTypes: Set<String>, standardTypes: Set<String> = standardTypes()): String = when {
+    startsWith("Union<") -> UnionType("", splitUnionType(this)).name.dynamicIfUnknownType(allTypes, standardTypes).copyNullabilityFrom(this)
+    endsWith("?") -> this.dropNullable().dynamicIfUnknownType(allTypes, standardTypes).ensureNullable()
+    contains("->") -> {
+        val (parameters, returnType) = this.split("->".toRegex()).map {it.trim()}.filter { it != "" }
+
+        "(${parameters.removeSurrounding("(", ")").split(',').map {it.dynamicIfUnknownType(allTypes, standardTypes)}.join(",")}) -> ${returnType.dynamicIfUnknownType(allTypes, standardTypes)}"
+    }
+    this in allTypes -> this
+    this in standardTypes -> this
+    else -> "dynamic"
+}
 
 private fun mapType(repository: Repository, type: String): String =
     when {
         type in typeMapper -> typeMapper[type]!!
-        type.endsWith("?") -> mapType(repository, type.substring(0, type.length() - 1)).ensureNullable()
+        type.endsWith("?") -> mapType(repository, type.dropNullable()).ensureNullable()
         type.endsWith("...") -> mapType(repository, type.substring(0, type.length() - 3))
         type.endsWith("[]") -> "Array<${mapType(repository, type.substring(0, type.length() - 2))}>"
         type.startsWith("unrestricted") -> mapType(repository, type.substring(12))