diff --git a/smnp/ast/node/expression.py b/smnp/ast/node/expression.py
index db939bc..c1c4382 100644
--- a/smnp/ast/node/expression.py
+++ b/smnp/ast/node/expression.py
@@ -1,4 +1,6 @@
-from smnp.ast.node.operator import BinaryOperator
+from smnp.ast.node.model import Node
+from smnp.ast.node.none import NoneNode
+from smnp.ast.node.operator import BinaryOperator, Operator
 from smnp.ast.node.term import TermParser
 from smnp.ast.parser import Parser
 from smnp.token.type import TokenType
@@ -20,7 +22,34 @@ class Or(BinaryOperator):
     pass
 
 
-def ExpressionParser(input):
+class Loop(BinaryOperator):
+    def __init__(self, pos):
+        super().__init__(pos)
+        self.children.append(NoneNode())
+
+    @property
+    def parameters(self):
+        return self[3]
+
+    @parameters.setter
+    def parameters(self, value):
+        self[3] = value
+
+    @classmethod
+    def loop(cls, left, parameters, operator, right):
+        node = cls(left.pos)
+        node.left = left
+        node.parameters = parameters
+        node.operator = operator
+        node.right = right
+        return node
+
+
+class LoopParameters(Node):
+    pass
+
+
+def ExpressionWithoutLoopParser(input):
     expr1 = Parser.leftAssociativeOperatorParser(
         TermParser,
         [TokenType.PLUS, TokenType.MINUS],
@@ -49,3 +78,34 @@ def ExpressionParser(input):
         lambda left, op, right: Or.withValues(left, op, right)
     )(input)
 
+
+def LoopParser(input):
+    from smnp.ast.node.identifier import IdentifierLiteralParser
+    from smnp.ast.node.iterable import abstractIterableParser
+    from smnp.ast.node.statement import StatementParser
+
+    loopParameters = Parser.allOf(
+        Parser.terminal(TokenType.AS),
+        Parser.oneOf(
+            Parser.wrap(IdentifierLiteralParser, lambda id: LoopParameters.withChildren([id], id.pos)),
+            abstractIterableParser(LoopParameters, TokenType.OPEN_PAREN, TokenType.CLOSE_PAREN, IdentifierLiteralParser)
+        ),
+        createNode=lambda asKeyword, parameters: parameters,
+        name="loop parameters"
+    )
+
+    return Parser.allOf(
+        ExpressionWithoutLoopParser,
+        Parser.optional(loopParameters),
+        Parser.terminal(TokenType.DASH, createNode=Operator.withValue),
+        StatementParser,
+        createNode=Loop.loop,
+        name="dash-loop"
+    )(input)
+
+
+def ExpressionParser(input):
+    return Parser.oneOf(
+        LoopParser,
+        ExpressionWithoutLoopParser
+    )(input)
diff --git a/smnp/ast/node/factor.py b/smnp/ast/node/factor.py
index afc78e4..404a4f3 100644
--- a/smnp/ast/node/factor.py
+++ b/smnp/ast/node/factor.py
@@ -1,6 +1,3 @@
-from smnp.ast.node.iterable import abstractIterableParser
-from smnp.ast.node.model import Node
-from smnp.ast.node.none import NoneNode
 from smnp.ast.node.operator import BinaryOperator, Operator, UnaryOperator
 from smnp.ast.node.unit import UnitParser
 from smnp.ast.parser import Parser
@@ -13,38 +10,8 @@ class NotOperator(UnaryOperator):
 class Power(BinaryOperator):
     pass
 
-
-class Loop(BinaryOperator):
-    def __init__(self, pos):
-        super().__init__(pos)
-        self.children.append(NoneNode())
-
-    @property
-    def parameters(self):
-        return self[3]
-
-    @parameters.setter
-    def parameters(self, value):
-        self[3] = value
-
-    @classmethod
-    def loop(cls, left, parameters, operator, right):
-        node = cls(left.pos)
-        node.left = left
-        node.parameters = parameters
-        node.operator = operator
-        node.right = right
-        return node
-
-
-class LoopParameters(Node):
-    pass
-
-
 def FactorParser(input):
     from smnp.ast.node.expression import ExpressionParser
-    from smnp.ast.node.statement import StatementParser
-    from smnp.ast.node.identifier import IdentifierLiteralParser
 
     parentheses = Parser.allOf(
         Parser.terminal(TokenType.OPEN_PAREN),
@@ -75,27 +42,7 @@ def FactorParser(input):
         name="not"
     )
 
-    loopParameters = Parser.allOf(
-        Parser.terminal(TokenType.AS),
-        Parser.oneOf(
-            Parser.wrap(IdentifierLiteralParser, lambda id: LoopParameters.withChildren([id], id.pos)),
-            abstractIterableParser(LoopParameters, TokenType.OPEN_PAREN, TokenType.CLOSE_PAREN, IdentifierLiteralParser)
-        ),
-        createNode=lambda asKeyword, parameters: parameters,
-        name="loop parameters"
-    )
-
-    loopFactor = Parser.allOf(
-        powerFactor,
-        Parser.optional(loopParameters),
-        Parser.terminal(TokenType.DASH, createNode=Operator.withValue),
-        StatementParser,
-        createNode=Loop.loop,
-        name="dash-loop"
-    )
-
     return Parser.oneOf(
-        loopFactor,
         notOperator,
         powerFactor,
         name="factor"
diff --git a/smnp/ast/node/function.py b/smnp/ast/node/function.py
index c0fcfa3..148ba8c 100644
--- a/smnp/ast/node/function.py
+++ b/smnp/ast/node/function.py
@@ -1,4 +1,5 @@
 from smnp.ast.node.block import BlockParser
+from smnp.ast.node.expression import ExpressionParser
 from smnp.ast.node.identifier import IdentifierLiteralParser
 from smnp.ast.node.iterable import abstractIterableParser
 from smnp.ast.node.model import Node
@@ -16,7 +17,7 @@ class Argument(Node):
 
     def __init__(self, pos):
         super().__init__(pos)
-        self.children = [NoneNode(), NoneNode(), False]
+        self.children = [NoneNode(), NoneNode(), False, NoneNode()]
 
     @property
     def type(self):
@@ -48,6 +49,14 @@ class Argument(Node):
         self[2] = value
 
 
+    @property
+    def optionalValue(self):
+        return self[3]
+
+    @optionalValue.setter
+    def optionalValue(self, value):
+        self[3] = value
+
 class VarargNode(Node):
     pass
 
@@ -90,7 +99,7 @@ class FunctionDefinition(Node):
         return node
 
 
-def ArgumentParser(input):
+def RegularArgumentParser(input):
     def createNode(type, variable, vararg):
         pos = type.pos if isinstance(type, Type) else variable.pos
         node = Argument(pos)
@@ -104,6 +113,33 @@ def ArgumentParser(input):
         Parser.doAssert(IdentifierLiteralParser, "argument name"),
         Parser.optional(Parser.terminal(TokenType.DOTS, lambda val, pos: True)),
         createNode=createNode,
+        name="regular function argument"
+    )(input)
+
+
+def OptionalArgumentParser(input):
+    def createNode(type, variable, _, optional):
+        pos = type.pos if isinstance(type, Type) else variable.pos
+        node = Argument(pos)
+        node.type = type
+        node.variable = variable
+        node.optionalValue = optional
+        return node
+
+    return Parser.allOf(
+        Parser.optional(TypeParser),
+        Parser.doAssert(IdentifierLiteralParser, "argument name"),
+        Parser.terminal(TokenType.ASSIGN),
+        Parser.doAssert(ExpressionParser, "expression"),
+        createNode=createNode,
+        name="optional function argument"
+    )(input)
+
+
+def ArgumentParser(input):
+    return Parser.oneOf(
+        OptionalArgumentParser,
+        RegularArgumentParser,
         name="function argument"
     )(input)
 
diff --git a/smnp/ast/node/statement.py b/smnp/ast/node/statement.py
index dc0d922..23d3996 100644
--- a/smnp/ast/node/statement.py
+++ b/smnp/ast/node/statement.py
@@ -1,5 +1,6 @@
 from smnp.ast.node.model import Node
 from smnp.ast.parser import Parser
+from smnp.token.type import TokenType
 
 
 class Statement(Node):
@@ -13,11 +14,24 @@ def StatementParser(input):
     from smnp.ast.node.ret import ReturnParser
     from smnp.ast.node.throw import ThrowParser
 
-    return Parser.oneOf(
-        IfElseStatementParser,
-        ExpressionParser,
-        BlockParser,
-        ReturnParser,
-        ThrowParser,
-        name="statement"
-    )(input)
+    return withSemicolon(
+        Parser.oneOf(
+            IfElseStatementParser,
+            ExpressionParser,  # Must be above BlockParser because of Map's syntax with curly braces
+            BlockParser,
+            ReturnParser,
+            ThrowParser,
+            name="statement"
+        ), optional=True)(input)
+
+
+def withSemicolon(parser, optional=False, doAssert=False):
+    semicolonParser = Parser.optional(Parser.terminal(TokenType.SEMICOLON)) if optional else Parser.terminal(
+        TokenType.SEMICOLON, doAssert=doAssert)
+
+    return Parser.allOf(
+        parser,
+        semicolonParser,
+        createNode=lambda stmt, semicolon: stmt,
+        name="semicolon" + "?" if optional else ""
+    )
diff --git a/smnp/environment/environment.py b/smnp/environment/environment.py
index fff3799..3a34531 100644
--- a/smnp/environment/environment.py
+++ b/smnp/environment/environment.py
@@ -40,7 +40,8 @@ class Environment():
             if method.typeSignature.check([object])[0] and method.name == name: #Todo sprawdzic sygnature typu
                 signatureCheckresult = method.signature.check(args)
                 if signatureCheckresult[0]:
-                    self.scopes.append({argName: argValue for argName, argValue in zip(method.arguments, list(signatureCheckresult[1:]))})
+                    self.scopes.append(method.defaultArgs)
+                    self.scopes[-1].update({argName: argValue for argName, argValue in zip(method.arguments, list(signatureCheckresult[1:]))})
                     self.scopes[-1][method.alias] = object
                     self.callStack.append(CallStackItem(name))
                     result = Type.void()
@@ -80,7 +81,8 @@ class Environment():
             if function.name == name:
                 signatureCheckresult = function.signature.check(args)
                 if signatureCheckresult[0]:
-                    self.scopes.append({ argName: argValue for argName, argValue in zip(function.arguments, list(signatureCheckresult[1:])) })
+                    self.scopes.append(function.defaultArgs)
+                    self.scopes[-1].update({ argName: argValue for argName, argValue in zip(function.arguments, list(signatureCheckresult[1:])) })
                     self.callStack.append(CallStackItem(name))
                     result = Type.void()
                     try:
@@ -93,11 +95,11 @@ class Environment():
                 raise IllegalFunctionInvocationException(f"{function.name}{function.signature.string}", f"{name}{argsTypesToString(args)}")
         return (False, None)
 
-    def addCustomFunction(self, name, signature, arguments, body):
+    def addCustomFunction(self, name, signature, arguments, body, defaultArguments):
         if len([fun for fun in self.functions + self.customFunctions if fun.name == name]) > 0:
             raise RuntimeException(f"Cannot redeclare function '{name}'", None)
 
-        self.customFunctions.append(CustomFunction(name, signature, arguments, body))
+        self.customFunctions.append(CustomFunction(name, signature, arguments, body, defaultArguments))
 
     # TODO:
     # There is still problem with checking existing of generic types, like lists:
@@ -108,14 +110,14 @@ class Environment():
     #   function foo() { return 2 }
     # }
     # Then calling [1, 2, 3, 4].foo() will produce 1, when the second method is more suitable
-    def addCustomMethod(self, typeSignature, alias, name, signature, arguments, body):
+    def addCustomMethod(self, typeSignature, alias, name, signature, arguments, body, defaultArguments):
         if len([m for m in self.methods if m.name == name and m.signature.matchers[0] == typeSignature.matchers[0]]) > 0:
             raise RuntimeException(f"Cannot redeclare method '{name}' for type '{typeSignature.matchers[0]}'", None)
 
         if len([m for m in self.customMethods if m.name == name and m.typeSignature.matchers[0] == typeSignature.matchers[0]]) > 0:
             raise RuntimeException(f"Cannot redeclare method '{name}' for type '{typeSignature.matchers[0]}'", None)
 
-        self.customMethods.append(CustomMethod(typeSignature, alias, name, signature, arguments, body))
+        self.customMethods.append(CustomMethod(typeSignature, alias, name, signature, arguments, body, defaultArguments))
 
     def findVariable(self, name, type=None, pos=None):
         for scope in reversed(self.scopes):
@@ -175,18 +177,20 @@ class CallStackItem:
 
 
 class CustomFunction:
-    def __init__(self, name, signature, arguments, body):
+    def __init__(self, name, signature, arguments, body, defaultArgs):
         self.name = name
         self.signature = signature
         self.arguments = arguments
         self.body = body
+        self.defaultArgs = defaultArgs
 
 
 class CustomMethod:
-    def __init__(self, typeSignature, alias, name, signature, arguments, body):
+    def __init__(self, typeSignature, alias, name, signature, arguments, body, defaultArgs):
         self.typeSignature = typeSignature
         self.alias = alias
         self.name = name
         self.signature = signature
         self.arguments = arguments
-        self.body = body
\ No newline at end of file
+        self.body = body
+        self.defaultArgs = defaultArgs
\ No newline at end of file
diff --git a/smnp/function/signature.py b/smnp/function/signature.py
index ad23caf..0c0bb9e 100644
--- a/smnp/function/signature.py
+++ b/smnp/function/signature.py
@@ -12,6 +12,9 @@ class Signature:
 
 def varargSignature(varargMatcher, *basicSignature, wrapVarargInValue=False):
     def check(args):
+        if any([ matcher.optional for matcher in [ varargMatcher, *basicSignature ]]):
+            raise RuntimeError("Vararg signature can't have optional arguments")
+
         if len(basicSignature) > len(args):
             return doesNotMatchVararg(basicSignature)
 
@@ -38,7 +41,7 @@ def doesNotMatchVararg(basicSignature):
 
 def signature(*signature):
     def check(args):
-        if len(signature) != len(args):
+        if len(args) > len(signature) or len(args) < len([ matcher for matcher in signature if not matcher.optional ]):
             return doesNotMatch(signature)
 
         for s, a in zip(signature, args):
@@ -52,6 +55,12 @@ def signature(*signature):
     return Signature(check, string, signature)
 
 
+def optional(matcher):
+    matcher.optional = True
+    matcher.string += "?"
+    return matcher
+
+
 def doesNotMatch(sign):
     return (False, *[None for n in sign])
 
diff --git a/smnp/main.py b/smnp/main.py
index d0b5b55..94025a1 100644
--- a/smnp/main.py
+++ b/smnp/main.py
@@ -9,9 +9,6 @@ def main():
     try:
         stdLibraryEnv = loadStandardLibrary()
         Interpreter.interpretFile(sys.argv[1], printTokens=False, printAst=False, execute=True, baseEnvironment=stdLibraryEnv)
-        #draft()
-        #tokens = tokenize(['function a(b...) { x+y}'])
-        #FunctionDefinitionParser(tokens).node.print()
 
     except SmnpException as e:
         print(e.message())
diff --git a/smnp/module/iterable/__init__.py b/smnp/module/iterable/__init__.py
index a3fc3b2..d302af9 100644
--- a/smnp/module/iterable/__init__.py
+++ b/smnp/module/iterable/__init__.py
@@ -1,4 +1,4 @@
-from smnp.module.iterable.function import combine, map, range, get
+from smnp.module.iterable.function import combine, map, get
 
-functions = [ combine.function, map.function, range.function ]
+functions = [ combine.function, map.function ]
 methods = [ get.function ]
\ No newline at end of file
diff --git a/smnp/runtime/evaluators/expression.py b/smnp/runtime/evaluators/expression.py
index e0758fa..46b70b6 100644
--- a/smnp/runtime/evaluators/expression.py
+++ b/smnp/runtime/evaluators/expression.py
@@ -1,6 +1,6 @@
 from smnp.ast.node.condition import IfElse
-from smnp.ast.node.expression import Sum, Relation, And, Or
-from smnp.ast.node.factor import NotOperator, Power, Loop
+from smnp.ast.node.expression import Sum, Relation, And, Or, Loop
+from smnp.ast.node.factor import NotOperator, Power
 from smnp.ast.node.identifier import FunctionCall, Assignment
 from smnp.ast.node.term import Product
 from smnp.ast.node.unit import MinusOperator, Access
@@ -50,3 +50,15 @@ def expressionEvaluator(doAssert=False):
 
 
     return evaluateExpression
+
+
+def expressionEvaluatorWithMatcher(matcher, exceptionProvider, doAssert=True):
+    def evaluate(node, environment):
+        value = expressionEvaluator(doAssert=doAssert)(node, environment).value
+
+        if not matcher.match(value):
+            raise exceptionProvider(value)
+
+        return value
+
+    return evaluate
\ No newline at end of file
diff --git a/smnp/runtime/evaluators/extend.py b/smnp/runtime/evaluators/extend.py
index 546487c..7f8a546 100644
--- a/smnp/runtime/evaluators/extend.py
+++ b/smnp/runtime/evaluators/extend.py
@@ -32,8 +32,8 @@ class ExtendEvaluator(Evaluator):
     @classmethod
     def _evaluateMethodDefinition(cls, node, environment, type, variable):
         name = node.name.value
-        signature = argumentsNodeToMethodSignature(node.arguments)
+        defaultArguments, signature = argumentsNodeToMethodSignature(node.arguments, environment)
         arguments = [arg.variable.value for arg in node.arguments]
         body = node.body
-        environment.addCustomMethod(type, variable, name, signature, arguments, body)
+        environment.addCustomMethod(type, variable, name, signature, arguments, body, defaultArguments)
 
diff --git a/smnp/runtime/evaluators/function.py b/smnp/runtime/evaluators/function.py
index 378598a..6b59ca1 100644
--- a/smnp/runtime/evaluators/function.py
+++ b/smnp/runtime/evaluators/function.py
@@ -25,10 +25,10 @@ class FunctionDefinitionEvaluator(Evaluator):
     def evaluator(cls, node, environment):
         try:
             name = node.name.value
-            signature = argumentsNodeToMethodSignature(node.arguments)
+            defaultArguments, signature = argumentsNodeToMethodSignature(node.arguments, environment)
             arguments = [ arg.variable.value for arg in node.arguments ]
             body = node.body
-            environment.addCustomFunction(name, signature, arguments, body)
+            environment.addCustomFunction(name, signature, arguments, body, defaultArguments)
         except RuntimeException as e:
             raise updatePos(e, node)
 
diff --git a/smnp/runtime/tools/signature.py b/smnp/runtime/tools/signature.py
index baf8d35..3cef1b5 100644
--- a/smnp/runtime/tools/signature.py
+++ b/smnp/runtime/tools/signature.py
@@ -2,7 +2,8 @@ from smnp.ast.node import type as ast
 from smnp.ast.node.none import NoneNode
 from smnp.ast.node.type import TypesList
 from smnp.error.runtime import RuntimeException
-from smnp.function.signature import varargSignature, signature
+from smnp.function.signature import varargSignature, signature, optional
+from smnp.runtime.evaluators.expression import expressionEvaluator, expressionEvaluatorWithMatcher
 from smnp.runtime.tools.error import updatePos
 from smnp.type.model import Type
 from smnp.type.signature.matcher.list import listOfMatchers
@@ -10,11 +11,19 @@ from smnp.type.signature.matcher.map import mapOfMatchers
 from smnp.type.signature.matcher.type import allTypes, oneOf, ofType
 
 
-def argumentsNodeToMethodSignature(node):
+def evaluateDefaultArguments(node, environment):
+    defaultValues = { arg.variable.value: expressionEvaluator(doAssert=True)(arg.optionalValue, environment).value for arg in node.children if type(arg.optionalValue) != NoneNode }
+
+    return defaultValues
+
+
+def argumentsNodeToMethodSignature(node, environment):
     try:
         sign = []
         vararg = None
         argumentsCount = len(node.children)
+        checkPositionOfOptionalArguments(node)
+        defaultArgs = {}
         for i, child in enumerate(node.children):
             matchers = {
                 ast.Type: (lambda c: c.type, typeMatcher),
@@ -22,19 +31,34 @@ def argumentsNodeToMethodSignature(node):
                 TypesList: (lambda c: c, multipleTypeMatcher)
             }
             evaluatedMatcher = matchers[type(child.type)][1](matchers[type(child.type)][0](child))
+
             if child.vararg:
                 if i != argumentsCount - 1:
                     raise RuntimeException("Vararg must be the last argument in signature", child.pos)
                 vararg = evaluatedMatcher
             else:
+                if type(child.optionalValue) != NoneNode:
+                    defaultArgs[child.variable.value] = expressionEvaluatorWithMatcher(
+                        evaluatedMatcher,
+                        exceptionProvider=lambda value: RuntimeException(
+                            f"Value '{value.stringify()}' doesn't match declared type: {evaluatedMatcher.string}", child.optionalValue.pos)
+                    )(child.optionalValue, environment)
+                    evaluatedMatcher = optional(evaluatedMatcher)
                 sign.append(evaluatedMatcher)
 
-
-        return varargSignature(vararg, *sign, wrapVarargInValue=True) if vararg is not None else signature(*sign)
+        return defaultArgs, (varargSignature(vararg, *sign, wrapVarargInValue=True) if vararg is not None else signature(*sign))
     except RuntimeException as e:
         raise updatePos(e, node)
 
 
+def checkPositionOfOptionalArguments(node):
+    firstOptional = next((i for i, v in enumerate(node.children) if type(v.optionalValue) != NoneNode), None) #next(filter(lambda arg: type(arg.optionalValue) != NoneNode, node.children), None)
+    if firstOptional is not None:
+        regularAfterOptional = next((i for i, v in enumerate(node.children[firstOptional:]) if type(v.optionalValue) == NoneNode), None)
+        if regularAfterOptional is not None:
+            raise RuntimeException(f"Optional arguments should be declared at the end of the arguments list", node.children[regularAfterOptional].pos)
+
+
 def multipleTypeMatcher(typeNode):
     subSignature = []
 
diff --git a/smnp/token/tokenizer.py b/smnp/token/tokenizer.py
index 017b88a..7c91ab1 100644
--- a/smnp/token/tokenizer.py
+++ b/smnp/token/tokenizer.py
@@ -27,6 +27,7 @@ tokenizers = (
     defaultTokenizer(TokenType.CLOSE_SQUARE),
     defaultTokenizer(TokenType.OPEN_ANGLE),
     defaultTokenizer(TokenType.CLOSE_ANGLE),
+    defaultTokenizer(TokenType.SEMICOLON),
     defaultTokenizer(TokenType.ASTERISK),
     defaultTokenizer(TokenType.ASSIGN),
     defaultTokenizer(TokenType.COMMA),
diff --git a/smnp/token/type.py b/smnp/token/type.py
index 7c47bc2..91b4811 100644
--- a/smnp/token/type.py
+++ b/smnp/token/type.py
@@ -12,6 +12,7 @@ class TokenType(Enum):
     CLOSE_SQUARE = ']'
     OPEN_ANGLE = '<'
     CLOSE_ANGLE = '>'
+    SEMICOLON = ';'
     ASTERISK = '*'
     ASSIGN = '='
     ARROW = '->'
diff --git a/smnp/type/signature/matcher/model.py b/smnp/type/signature/matcher/model.py
index 4e68860..17535ad 100644
--- a/smnp/type/signature/matcher/model.py
+++ b/smnp/type/signature/matcher/model.py
@@ -3,6 +3,7 @@ class Matcher:
         self.type = objectType
         self.matcher = matcher
         self.string = string
+        self.optional = False
 
     def match(self, value):
         if self.type is not None and self.type != value.type:
diff --git a/smnp/type/signature/matcher/type.py b/smnp/type/signature/matcher/type.py
index 8416a74..f374186 100644
--- a/smnp/type/signature/matcher/type.py
+++ b/smnp/type/signature/matcher/type.py
@@ -25,4 +25,4 @@ def oneOf(*matchers):
     def check(value):
         return any(matcher.match(value) for matcher in matchers)
 
-    return Matcher(None, check, f"<{', '.join(m.string for m in matchers)}>")
\ No newline at end of file
+    return Matcher(None, check, f"<{', '.join(m.string for m in matchers)}>")