diff --git a/example/interop/bindings.nub b/example/interop/bindings.nub
index e164518..08144f4 100644
--- a/example/interop/bindings.nub
+++ b/example/interop/bindings.nub
@@ -1,5 +1,6 @@
 namespace c
 
+extern func printf(fmt: string, ...args: any)
 extern func printf(fmt: string, ...args: any)
 extern func getchar(): i32
 extern func puts(str: string)
diff --git a/src/compiler/Nub.Lang/Backend/Generator.cs b/src/compiler/Nub.Lang/Backend/Generator.cs
index 05b6430..5c053ea 100644
--- a/src/compiler/Nub.Lang/Backend/Generator.cs
+++ b/src/compiler/Nub.Lang/Backend/Generator.cs
@@ -6,31 +6,35 @@ namespace Nub.Lang.Backend;
 
 public class Generator
 {
-    private readonly List<DefinitionNode> _definitions;
-    private readonly StringBuilder _builder = new();
-    private readonly Dictionary<string, Variable> _variables = new();
-    private readonly List<string> _strings = [];
-    private readonly Stack<string> _breakLabels = new();
-    private readonly Stack<string> _continueLabels = new();
+    private List<SourceFile> _sourceFiles = [];
+    private StringBuilder _builder = new();
+    private Dictionary<string, Variable> _variables = [];
+    private List<string> _strings = [];
+    private Stack<string> _breakLabels = [];
+    private Stack<string> _continueLabels = [];
     private int _variableIndex;
     private bool _codeIsReachable = true;
 
-    public Generator(List<DefinitionNode> definitions)
+    public string Generate(List<SourceFile> sourceFiles)
     {
-        _definitions = definitions;
-    }
-
-    public string Generate()
-    {
-        foreach (var structDefinition in _definitions.OfType<StructDefinitionNode>())
+        _sourceFiles = sourceFiles;
+        _builder = new StringBuilder();
+        _variables = new Dictionary<string, Variable>();
+        _strings = [];
+        _breakLabels = [];
+        _continueLabels = [];
+        _variableIndex = 0;
+        _codeIsReachable = true;
+        
+        foreach (var structDef in _sourceFiles.SelectMany(f => f.Definitions).OfType<StructDefinitionNode>())
         {
-            GenerateStructDefinition(structDefinition);
+            GenerateStructDefinition(structDef);
             _builder.AppendLine();
         }
 
-        foreach (var funcDefinition in _definitions.OfType<LocalFuncDefinitionNode>())
+        foreach (var funcDef in _sourceFiles.SelectMany(f => f.Definitions).OfType<LocalFuncDefinitionNode>())
         {
-            GenerateFuncDefinition(funcDefinition);
+            GenerateFuncDefinition(funcDef);
             _builder.AppendLine();
         }
 
@@ -213,12 +217,12 @@ public class Generator
                         throw new ArgumentOutOfRangeException();
                 }
             }
-            case NubStructType nubCustomType:
+            case NubStructType nubStructType:
             {
-                var definition = _definitions.OfType<StructDefinitionNode>().FirstOrDefault(s => s.Name == nubCustomType.Name);
+                var definition = LookupStructDefinition(nubStructType.Namespace, nubStructType.Name);
                 if (definition == null)
                 {
-                    throw new Exception($"Cannot determine size of non-existent type {nubCustomType}");
+                    throw new Exception($"Cannot determine size of non-existent type {nubStructType}");
                 }
 
                 return definition.Fields.Sum(f => QbeTypeSize(f.Type));
@@ -362,12 +366,8 @@ public class Generator
 
     private string GenerateFuncCall(FuncCall funcCall)
     {
-        var parameterDefinitions = _definitions
-            .OfType<IFuncSignature>()
-            .FirstOrDefault(d => d.Name == funcCall.Name)
-            ?.Parameters;
-
-        if (parameterDefinitions == null)
+        var funcDefinition = LookupFuncSignature(funcCall.Namespace, funcCall.Name, funcCall.Parameters.Select(p => p.Type).ToList());
+        if (funcDefinition == null)
         {
             throw new Exception($"Unknown function {funcCall}");
         }
@@ -376,19 +376,19 @@ public class Generator
 
         for (var i = 0; i < funcCall.Parameters.Count; i++)
         {
-            if (i < parameterDefinitions.Count && parameterDefinitions[i].Variadic)
+            if (i < funcDefinition.Parameters.Count && funcDefinition.Parameters[i].Variadic)
             {
                 parameterStrings.Add("...");
             }
 
             NubType expectedType;
-            if (i < parameterDefinitions.Count)
+            if (i < funcDefinition.Parameters.Count)
             {
-                expectedType = parameterDefinitions[i].Type;
+                expectedType = funcDefinition.Parameters[i].Type;
             }
-            else if (parameterDefinitions[^1].Variadic)
+            else if (funcDefinition.Parameters[^1].Variadic)
             {
-                expectedType = parameterDefinitions[^1].Type;
+                expectedType = funcDefinition.Parameters[^1].Type;
             }
             else
             {
@@ -1295,7 +1295,7 @@ public class Generator
 
     private string GenerateStructInitializer(StructInitializerNode structInitializer)
     {
-        var structDefinition = _definitions.OfType<StructDefinitionNode>().FirstOrDefault(s => s.Name == structInitializer.StructType.Name);
+        var structDefinition = LookupStructDefinition(structInitializer.StructType.Namespace, structInitializer.StructType.Name);
         if (structDefinition == null)
         {
             throw new Exception($"Struct {structInitializer.StructType.Name} is not defined");
@@ -1399,10 +1399,7 @@ public class Generator
             }
             case NubStructType structType:
             {
-                var structDefinition = _definitions
-                    .OfType<StructDefinitionNode>()
-                    .FirstOrDefault(s => s.Name == structType.Name);
-
+                var structDefinition = LookupStructDefinition(structType.Namespace, structType.Namespace);
                 if (structDefinition == null)
                 {
                     throw new Exception($"Struct {structType.Name} is not defined");
@@ -1449,6 +1446,24 @@ public class Generator
         return $"v{++_variableIndex}";
     }
 
+    private IFuncSignature? LookupFuncSignature(string @namespace, string name, List<NubType> parameters)
+    {
+        return _sourceFiles
+            .Where(f => f.Namespace == @namespace)
+            .SelectMany(f => f.Definitions)
+            .OfType<IFuncSignature>()
+            .FirstOrDefault(f => f.SignatureMatches(name, parameters));
+    }
+
+    private StructDefinitionNode? LookupStructDefinition(string @namespace, string name)
+    {
+        return _sourceFiles
+            .Where(f => f.Namespace == @namespace)
+            .SelectMany(f => f.Definitions)
+            .OfType<StructDefinitionNode>()
+            .FirstOrDefault(d => d.Name == name);
+    }
+
     private class Variable
     {
         public required string Pointer { get; init; }
diff --git a/src/compiler/Nub.Lang/Frontend/Parsing/FuncDefinitionNode.cs b/src/compiler/Nub.Lang/Frontend/Parsing/FuncDefinitionNode.cs
index bcfbc56..3cf9977 100644
--- a/src/compiler/Nub.Lang/Frontend/Parsing/FuncDefinitionNode.cs
+++ b/src/compiler/Nub.Lang/Frontend/Parsing/FuncDefinitionNode.cs
@@ -8,10 +8,41 @@ public interface IFuncSignature
     public List<FuncParameter> Parameters { get; }
     public Optional<NubType> ReturnType { get; }
 
+    public bool SignatureMatches(string name, List<NubType> parameters)
+    {
+        if (Name != name) return false;
+        if (Parameters.Count == 0 && parameters.Count == 0) return true;
+        if (Parameters.Count > parameters.Count) return false;
+            
+        for (var i = 0; i < parameters.Count; i++)
+        {
+            if (i > Parameters.Count)
+            {
+                if (Parameters[^1].Variadic)
+                {
+                    if (!NubType.IsCompatibleWith(parameters[i], Parameters[^1].Type))
+                    {
+                        return false;
+                    }
+                }
+                else
+                {
+                    return false;
+                }
+            }
+            else if (!NubType.IsCompatibleWith(parameters[i], Parameters[i].Type))
+            {
+                return false;
+            }
+        }
+            
+        return true;
+    }
+
     public string ToString() => $"{Name}({string.Join(", ", Parameters.Select(p => p.ToString()))}){(ReturnType.HasValue ? ": " + ReturnType.Value : "")}";
 }
 
-public class LocalFuncDefinitionNode(IReadOnlyList<Token> tokens, Optional<string> documentation, string name, List<FuncParameter> parameters, BlockNode body, Optional<NubType> returnType, bool global) : DefinitionNode(tokens, documentation)
+public class LocalFuncDefinitionNode(IReadOnlyList<Token> tokens, Optional<string> documentation, string name, List<FuncParameter> parameters, BlockNode body, Optional<NubType> returnType, bool global) : DefinitionNode(tokens, documentation), IFuncSignature
 {
     public string Name { get; } = name;
     public List<FuncParameter> Parameters { get; } = parameters;
diff --git a/src/compiler/Nub.Lang/Frontend/Parsing/Parser.cs b/src/compiler/Nub.Lang/Frontend/Parsing/Parser.cs
index dc92c18..112fef6 100644
--- a/src/compiler/Nub.Lang/Frontend/Parsing/Parser.cs
+++ b/src/compiler/Nub.Lang/Frontend/Parsing/Parser.cs
@@ -484,17 +484,36 @@ public class Parser
                     case Symbol.New:
                     {
                         var type = ParseType();
-                        Dictionary<string, ExpressionNode> initializers = [];
-                        ExpectSymbol(Symbol.OpenBrace);
-                        while (!TryExpectSymbol(Symbol.CloseBrace))
+                        switch (type)
                         {
-                            var name = ExpectIdentifier().Value;
-                            ExpectSymbol(Symbol.Assign);
-                            var value = ParseExpression();
-                            initializers.Add(name, value);
-                        }
+                            case NubStructType structType:
+                            {
+                                Dictionary<string, ExpressionNode> initializers = [];
+                                ExpectSymbol(Symbol.OpenBrace);
+                                while (!TryExpectSymbol(Symbol.CloseBrace))
+                                {
+                                    var name = ExpectIdentifier().Value;
+                                    ExpectSymbol(Symbol.Assign);
+                                    var value = ParseExpression();
+                                    initializers.Add(name, value);
+                                }
 
-                        expr = new StructInitializerNode(GetTokensForNode(startIndex), type, initializers);
+                                expr = new StructInitializerNode(GetTokensForNode(startIndex), structType, initializers);
+                                break;
+                            }
+                            case NubArrayType arrayType:
+                            {
+                                throw new NotImplementedException();
+                            }
+                            default:
+                            {
+                                throw new ParseException(Diagnostic
+                                        .Error($"Cannot use new keyword on type {type}")
+                                        .At(symbolToken)
+                                        .Build());
+                            }
+                        }
+                        
                         break;
                     }
                     case Symbol.Ampersand:
diff --git a/src/compiler/Nub.Lang/Frontend/Parsing/StructInitializerNode.cs b/src/compiler/Nub.Lang/Frontend/Parsing/StructInitializerNode.cs
index 6c8a0a3..894b641 100644
--- a/src/compiler/Nub.Lang/Frontend/Parsing/StructInitializerNode.cs
+++ b/src/compiler/Nub.Lang/Frontend/Parsing/StructInitializerNode.cs
@@ -2,8 +2,8 @@
 
 namespace Nub.Lang.Frontend.Parsing;
 
-public class StructInitializerNode(IReadOnlyList<Token> tokens, NubType structType, Dictionary<string, ExpressionNode> initializers) : ExpressionNode(tokens)
+public class StructInitializerNode(IReadOnlyList<Token> tokens, NubStructType structType, Dictionary<string, ExpressionNode> initializers) : ExpressionNode(tokens)
 {
-    public NubType StructType { get; } = structType;
+    public NubStructType StructType { get; } = structType;
     public Dictionary<string, ExpressionNode> Initializers { get; } = initializers;
 }
\ No newline at end of file
diff --git a/src/compiler/Nub.Lang/Frontend/Typing/TypeChecker.cs b/src/compiler/Nub.Lang/Frontend/Typing/TypeChecker.cs
index 4fb75af..e7978ff 100644
--- a/src/compiler/Nub.Lang/Frontend/Typing/TypeChecker.cs
+++ b/src/compiler/Nub.Lang/Frontend/Typing/TypeChecker.cs
@@ -11,7 +11,7 @@ public class TypeChecker
     private NubType? _currentFunctionReturnType;
     private bool _hasReturnStatement;
 
-    public DiagnosticsResult<List<DefinitionNode>> TypeCheck(List<SourceFile> sourceFiles)
+    public DiagnosticsResult TypeCheck(List<SourceFile> sourceFiles)
     {
         _variables = new Dictionary<string, NubType>();
         _diagnostics = [];
@@ -19,6 +19,16 @@ public class TypeChecker
         _hasReturnStatement = false;
         _sourceFiles = sourceFiles;
 
+        var externFunctionNames = _sourceFiles
+            .SelectMany(f => f.Definitions)
+            .OfType<ExternFuncDefinitionNode>()
+            .ToArray();
+
+        foreach (var funcName in externFunctionNames.Where(x => externFunctionNames.Count(y => x.Name == y.Name) > 1))
+        {
+            ReportError($"Extern function '{funcName}' has been declared more than once", funcName);
+        }
+        
         foreach (var structDef in _sourceFiles.SelectMany(f => f.Definitions).OfType<StructDefinitionNode>())
         {
             TypeCheckStructDef(structDef);
@@ -28,8 +38,8 @@ public class TypeChecker
         {
             TypeCheckFuncDef(funcDef);
         }
-
-        return new DiagnosticsResult<List<DefinitionNode>>(_diagnostics, _sourceFiles.SelectMany(f => f.Definitions).ToList());
+        
+        return new DiagnosticsResult(_diagnostics);
     }
 
     private void TypeCheckStructDef(StructDefinitionNode structDef)
@@ -120,14 +130,14 @@ public class TypeChecker
         {
             if (varAssign.ExplicitType.HasValue)
             {
-                if (!AreTypesCompatible(existingVariable, varAssign.ExplicitType.Value))
+                if (!NubType.IsCompatibleWith(existingVariable, varAssign.ExplicitType.Value))
                 {
                     ReportError($"Explicit type '{varAssign.ExplicitType.Value}' on variable '{varAssign.Name}' is not compatible with declared type '{existingVariable}'", varAssign);
                     return;
                 }
             }
                 
-            if (!AreTypesCompatible(valueType, existingVariable))
+            if (!NubType.IsCompatibleWith(valueType, existingVariable))
             {
                 ReportError($"Cannot assign expression of type '{valueType}' to variable '{varAssign.Name}' of type '{existingVariable}'", varAssign);
             }
@@ -137,7 +147,7 @@ public class TypeChecker
             if (varAssign.ExplicitType.HasValue)
             {
                 var explicitType = varAssign.ExplicitType.Value;
-                if (!AreTypesCompatible(valueType, explicitType))
+                if (!NubType.IsCompatibleWith(valueType, explicitType))
                 {
                     ReportError($"Cannot assign expression of type '{valueType}' to variable '{varAssign.Name}' of type '{explicitType}'", varAssign);
                     return;
@@ -208,7 +218,7 @@ public class TypeChecker
                 continue;
             }
 
-            if (!AreTypesCompatible(argType, paramType))
+            if (!NubType.IsCompatibleWith(argType, paramType))
             {
                 ReportError($"Parameter {i + 1} of function '{funcCall.Name}' expects type '{paramType}', but got '{argType}'", funcCall.Parameters[i]);
             }
@@ -260,7 +270,7 @@ public class TypeChecker
                 return;
             }
 
-            if (!AreTypesCompatible(returnType, _currentFunctionReturnType))
+            if (!NubType.IsCompatibleWith(returnType, _currentFunctionReturnType))
             {
                 ReportError($"Return value of type '{returnType}' is not compatible with function return type '{_currentFunctionReturnType}'", returnNode.Value.Value);
             }
@@ -405,17 +415,10 @@ public class TypeChecker
     {
         var initialized = new HashSet<string>();
 
-        var structType = structInit.StructType;
-        if (structType is not NubStructType customType)
-        {
-            ReportError($"Type '{structType}' is not a struct type", structInit);
-            return null;
-        }
-
-        var definition = LookupStructDefinition(customType.Namespace, customType.Name);
+        var definition = LookupStructDefinition(structInit.StructType.Namespace, structInit.StructType.Name);
         if (definition == null)
         {
-            ReportError($"Struct type '{customType.Name}' is not defined", structInit);
+            ReportError($"Struct type '{structInit.StructType.Name}' is not defined", structInit);
             return null;
         }
 
@@ -424,12 +427,12 @@ public class TypeChecker
             var definitionField = definition.Fields.FirstOrDefault(f => f.Name == initializer.Key);
             if (definitionField == null)
             {
-                ReportError($"Field '{initializer.Key}' does not exist in struct '{customType.Name}'", initializer.Value);
+                ReportError($"Field '{initializer.Key}' does not exist in struct '{structInit.StructType.Name}'", initializer.Value);
                 continue;
             }
 
             var initializerType = TypeCheckExpression(initializer.Value);
-            if (initializerType != null && !AreTypesCompatible(initializerType, definitionField.Type))
+            if (initializerType != null && !NubType.IsCompatibleWith(initializerType, definitionField.Type))
             {
                 ReportError($"Cannot initialize field '{initializer.Key}' of type '{definitionField.Type}' with expression of type '{initializerType}'", initializer.Value);
             }
@@ -446,11 +449,11 @@ public class TypeChecker
         {
             if (!initialized.Contains(field.Name))
             {
-                ReportError($"Struct field '{field.Name}' is not initialized on type '{customType.Name}'", structInit);
+                ReportError($"Struct field '{field.Name}' is not initialized on type '{structInit.StructType.Name}'", structInit);
             }
         }
 
-        return structType;
+        return structInit.StructType;
     }
 
     private NubType? TypeCheckUnaryExpression(UnaryExpressionNode unaryExpression)
@@ -539,11 +542,6 @@ public class TypeChecker
         _diagnostics.Add(diagnostic);
     }
 
-    private static bool AreTypesCompatible(NubType sourceType, NubType targetType)
-    {
-        return targetType.Equals(NubPrimitiveType.Any) || sourceType.Equals(targetType);
-    }
-
     private static bool IsNumeric(NubType type)
     {
         if (type is not NubPrimitiveType primitiveType)
@@ -598,38 +596,7 @@ public class TypeChecker
             .Where(f => f.Namespace == @namespace)
             .SelectMany(f => f.Definitions)
             .OfType<IFuncSignature>()
-            .FirstOrDefault(SignatureMatches);
-
-        bool SignatureMatches(IFuncSignature node)
-        {
-            if (node.Name != name) return false;
-            if (node.Parameters.Count == 0 && parameters.Count == 0) return true;
-            if (node.Parameters.Count > parameters.Count) return false;
-            
-            for (var i = 0; i < parameters.Count; i++)
-            {
-                if (i > node.Parameters.Count)
-                {
-                    if (node.Parameters[^1].Variadic)
-                    {
-                        if (!AreTypesCompatible(parameters[i], node.Parameters[^1].Type))
-                        {
-                            return false;
-                        }
-                    }
-                    else
-                    {
-                        return false;
-                    }
-                }
-                else if (!AreTypesCompatible(parameters[i], node.Parameters[i].Type))
-                {
-                    return false;
-                }
-            }
-            
-            return true;
-        }
+            .FirstOrDefault(f => f.SignatureMatches(name, parameters));
     }
 
     private StructDefinitionNode? LookupStructDefinition(string @namespace, string name)
diff --git a/src/compiler/Nub.Lang/NubType.cs b/src/compiler/Nub.Lang/NubType.cs
index c2b9777..0d58dd4 100644
--- a/src/compiler/Nub.Lang/NubType.cs
+++ b/src/compiler/Nub.Lang/NubType.cs
@@ -11,6 +11,11 @@ public abstract class NubType
 
     public string Name { get; }
 
+    public static bool IsCompatibleWith(NubType sourceType, NubType targetType)
+    {
+        return targetType.Equals(NubPrimitiveType.Any) || sourceType.Equals(targetType);
+    }
+    
     public override bool Equals(object? obj) => obj is NubType item && Name.Equals(item.Name);
     public override int GetHashCode() => HashCode.Combine(Name);
     public override string ToString() => Name;
diff --git a/src/compiler/Nub.Lang/Program.cs b/src/compiler/Nub.Lang/Program.cs
index 25631fd..10e9043 100644
--- a/src/compiler/Nub.Lang/Program.cs
+++ b/src/compiler/Nub.Lang/Program.cs
@@ -58,8 +58,8 @@ internal static class Program
         typeCheckResult.PrintAllDiagnostics();
         error = error || typeCheckResult.HasErrors;
 
-        var generator = new Generator(typeCheckResult.Value);
-        var result = generator.Generate();
+        var generator = new Generator();
+        var result = generator.Generate(files);
         
         Console.Out.Write(result);