diff --git a/Upsilon/BaseTypes/TypeConversion.cs b/Upsilon/BaseTypes/TypeConversion.cs
index e2cfc0d..715658e 100644
--- a/Upsilon/BaseTypes/TypeConversion.cs
+++ b/Upsilon/BaseTypes/TypeConversion.cs
@@ -42,5 +42,33 @@ namespace Upsilon.BaseTypes
             }
             return new GenericUserData(o);
         }
+
+        public static Type GetLuaType(object o)
+        {
+            if (o is ScriptType t)
+            {
+                return t.Type;
+            }
+
+            switch (o)
+            {
+                case bool _:
+                    return Type.Boolean;
+                case int _:
+                    return Type.Number;
+                case long _:
+                    return Type.Number;
+                case float _:
+                    return Type.Number;
+                case double _:
+                    return Type.Number;
+                case string _:
+                    return Type.String;
+                case null:
+                    return Type.Nil;
+                default:
+                    return Type.UserData;
+            }
+        }
     }
 }
\ No newline at end of file
diff --git a/Upsilon/Binder/Binder.cs b/Upsilon/Binder/Binder.cs
index c5772d0..836cee2 100644
--- a/Upsilon/Binder/Binder.cs
+++ b/Upsilon/Binder/Binder.cs
@@ -50,7 +50,11 @@ namespace Upsilon.Binder
                 }
                 unboundFunctionStatement.Value.Block =
                     (BoundBlockStatement) BindBlockStatement(unboundFunctionStatement.Value.UnboundBlock);
+                var resultType = Scope.ReturnType;
                 Scope                                      = Scope.ParentScope;
+                var variable = (FunctionVariableSymbol)Scope.Variables[unboundFunctionStatement.Key];
+                variable.IsBound = true;
+                variable.ResultType = resultType;
             }
             _unboundFunctions = new Dictionary<string, UnboundFunctionExpression>();
             return new BoundScript((BoundBlockStatement) bound, e.Span, Scope);
@@ -198,6 +202,7 @@ namespace Upsilon.Binder
                 parameters.Add(bound);
             }
 
+            var returnType = Type.Unknown;
             if (expression.Kind == BoundKind.VariableExpression)
             {
                 var variableExpression =(BoundVariableExpression) expression;
@@ -216,14 +221,18 @@ namespace Upsilon.Binder
                     var unboundFunctionStatement = _unboundFunctions[function.Name];
                     unboundFunctionStatement.Block =
                         (BoundBlockStatement) BindBlockStatement(unboundFunctionStatement.UnboundBlock);
+                    returnType = Scope.ReturnType;
                     Scope            = Scope.ParentScope;
                     function.IsBound = true;
+                    function.ResultType = returnType;
                     _unboundFunctions.Remove(function.Name);
                 }
+
+                returnType = function.ResultType;
             }
 
             //TODO: validate parameters
-            return new BoundFunctionCallExpression(expression, parameters.ToImmutable(), e.Span);
+            return new BoundFunctionCallExpression(expression, parameters.ToImmutable(), e.Span, returnType);
         }
 
         private BoundExpression BindVariableExpression(VariableExpressionSyntax e)
@@ -402,9 +411,10 @@ namespace Upsilon.Binder
             {
                 Scope = innerScope;
                 var block = BindBlockStatement(e.Block);
+                var returnType = Scope.ReturnType;
                 Scope = Scope.ParentScope;
                 var func = new BoundFunctionExpression(parameters.ToImmutable(), (BoundBlockStatement) block, e.Span,
-                    innerScope);
+                    innerScope, returnType);
                 return func;
             }
             else
@@ -445,7 +455,7 @@ namespace Upsilon.Binder
 
             if (!Scope.TryGetVariable(name, !isLocal, out var variable))
             {
-                var functionVariable = new FunctionVariableSymbol(name, Type.Function, isLocal, parameters.ToImmutable())
+                var functionVariable = new FunctionVariableSymbol(name, isLocal, parameters.ToImmutable(), func.ReturnType)
                 {
                     CommentValue = commentData.ToArray()
                 };
@@ -480,6 +490,17 @@ namespace Upsilon.Binder
         private BoundStatement BindReturnStatement(ReturnStatementSyntax e)
         {
             var expression = BindExpression(e.Expression);
+            if (expression.Type != Type.Unknown && expression.Type != Type.Unknown &&
+                Scope.ReturnType != Type.Unknown && Scope.ReturnType != Type.Nil)
+            {
+                if (expression.Type != Scope.ReturnType)
+                {
+                    _diagnostics.LogError($"Can't return type '{expression.Type}' from this scope, earlier in the" +
+                                          $" scope a return type of '{Scope.ReturnType}' is defined.", e.Span);
+                }
+            }
+            if (expression.Type != Type.Unknown && expression.Type != Type.Nil)
+                Scope.ReturnType = expression.Type;
             return new BoundReturnStatement(expression, e.Span);
         }
 
diff --git a/Upsilon/Binder/BoundExpressions/BoundFunctionCallExpression.cs b/Upsilon/Binder/BoundExpressions/BoundFunctionCallExpression.cs
index 6302772..e16a418 100644
--- a/Upsilon/Binder/BoundExpressions/BoundFunctionCallExpression.cs
+++ b/Upsilon/Binder/BoundExpressions/BoundFunctionCallExpression.cs
@@ -11,10 +11,11 @@ namespace Upsilon.Binder
         public ImmutableArray<BoundExpression> Parameters { get; }
 
         public BoundFunctionCallExpression(BoundExpression identifier, ImmutableArray<BoundExpression> parameters,
-            TextSpan span) : base(span)
+            TextSpan span, Type type) : base(span)
         {
             Identifier = identifier;
             Parameters = parameters;
+            Type = type;
         }
 
         public override BoundKind Kind => BoundKind.BoundFunctionCallExpression;
@@ -37,6 +38,6 @@ namespace Upsilon.Binder
             yield return this;
         }
 
-        public override Type Type => Type.Unknown;
+        public override Type Type { get; }
     }
 }
\ No newline at end of file
diff --git a/Upsilon/Binder/BoundExpressions/BoundFunctionExpression.cs b/Upsilon/Binder/BoundExpressions/BoundFunctionExpression.cs
index 49819ec..488e3a7 100644
--- a/Upsilon/Binder/BoundExpressions/BoundFunctionExpression.cs
+++ b/Upsilon/Binder/BoundExpressions/BoundFunctionExpression.cs
@@ -10,12 +10,13 @@ namespace Upsilon.Binder
         public ImmutableArray<BoundVariableSymbol> Parameters { get; }
         public BoundBlockStatement Block { get; set; }
 
-        public BoundFunctionExpression(ImmutableArray<BoundVariableSymbol> parameters, BoundBlockStatement block, TextSpan span,
-            BoundScope scope) : base(span)
+        public BoundFunctionExpression(ImmutableArray<BoundVariableSymbol> parameters, BoundBlockStatement block,
+            TextSpan span, BoundScope scope, Type returnType) : base(span)
         {
             Parameters = parameters;
             Block = block;
             Scope = scope;
+            ReturnType = returnType;
         }
 
         public override BoundKind Kind => BoundKind.BoundFunctionExpression;
@@ -35,5 +36,6 @@ namespace Upsilon.Binder
 
         public override Type Type => Type.Function;
         public BoundScope Scope { get; set; }
+        public Type ReturnType { get; }
     }
 }
\ No newline at end of file
diff --git a/Upsilon/Binder/BoundScope.cs b/Upsilon/Binder/BoundScope.cs
index dce4b43..25eeefc 100644
--- a/Upsilon/Binder/BoundScope.cs
+++ b/Upsilon/Binder/BoundScope.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using Type = Upsilon.BaseTypes.Type;
 
 namespace Upsilon.Binder
 {
@@ -8,6 +9,7 @@ namespace Upsilon.Binder
         public readonly BoundScope ParentScope;
         public BoundScope ReadOnlyScope { get; private set; }
         public readonly Dictionary<string, VariableSymbol> Variables;
+        public Type ReturnType { get; set; } = Type.Nil;
 
         public BoundScope(BoundScope parentScope)
         {
diff --git a/Upsilon/Binder/BoundStatements/UnboundFunctionExpression.cs b/Upsilon/Binder/BoundStatements/UnboundFunctionExpression.cs
index e563951..f2f3f95 100644
--- a/Upsilon/Binder/BoundStatements/UnboundFunctionExpression.cs
+++ b/Upsilon/Binder/BoundStatements/UnboundFunctionExpression.cs
@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
+using Upsilon.BaseTypes;
 using Upsilon.Parser;
 using Upsilon.Text;
 
@@ -8,7 +9,8 @@ namespace Upsilon.Binder
     public class UnboundFunctionExpression : BoundFunctionExpression
     {
         public UnboundFunctionExpression(ImmutableArray<BoundVariableSymbol> parameters,
-            BlockStatementSyntax unboundBlock, TextSpan span, BoundScope scope) : base(parameters, null, span, scope)
+            BlockStatementSyntax unboundBlock, TextSpan span, BoundScope scope)
+            : base(parameters, null, span, scope, Type.Unknown)
         {
             UnboundBlock = unboundBlock;
         }
diff --git a/Upsilon/Binder/VariableSymbol.cs b/Upsilon/Binder/VariableSymbol.cs
index eaac21e..276813b 100644
--- a/Upsilon/Binder/VariableSymbol.cs
+++ b/Upsilon/Binder/VariableSymbol.cs
@@ -23,12 +23,14 @@ namespace Upsilon.Binder
     public class FunctionVariableSymbol : VariableSymbol
     {
         public ImmutableArray<VariableSymbol> Parameters { get; }
+        public Type ResultType { get; internal set; }
         public bool IsBound { get; set; }
 
-        public FunctionVariableSymbol(string name, Type type, bool local, ImmutableArray<VariableSymbol> parameters)
-            : base(name, type, local)
+        public FunctionVariableSymbol(string name, bool local, ImmutableArray<VariableSymbol> parameters, Type resultType)
+            : base(name, Type.Function, local)
         {
             Parameters = parameters;
+            ResultType = resultType;
         }
     }
 
diff --git a/Upsilon/StandardLibraries/StaticScope.cs b/Upsilon/StandardLibraries/StaticScope.cs
index a5f2190..3308edd 100644
--- a/Upsilon/StandardLibraries/StaticScope.cs
+++ b/Upsilon/StandardLibraries/StaticScope.cs
@@ -46,8 +46,8 @@ namespace Upsilon.StandardLibraries
             var boundScope =
                 new BoundScope(
                     scope.Variables.ToDictionary(x => x.Key,
-                        x => (VariableSymbol) new FunctionVariableSymbol(x.Key, x.Value.Type, false,
-                            ImmutableArray<VariableSymbol>.Empty) {IsBound = true}),
+                        x => (VariableSymbol) new FunctionVariableSymbol(x.Key, false,
+                            ImmutableArray<VariableSymbol>.Empty, x.Value.Type) {IsBound = true}),
                     null);
             return (scope, boundScope);
         }