diff --git a/src/codegen/backend.c b/src/codegen/backend.c
index c305961..d2eccac 100644
--- a/src/codegen/backend.c
+++ b/src/codegen/backend.c
@@ -9,22 +9,35 @@ static struct CodegenBackend_t {
     const char* name;
 } CodegenBackend;
 
+BackendError new_backend_error(BackendErrorKind kind) {
+    return new_backend_impl_error(kind, NULL, NULL);
+}
+
+BackendError new_backend_impl_error(BackendErrorKind kind, AST_NODE_PTR node, const char* message) {
+    BackendError error;
+    error.kind = kind;
+    error.impl.ast_node = node;
+    error.impl.message = message;
+
+    return error;
+}
+
 BackendError init_backend(void) {
     DEBUG("initializing backend: %s", CodegenBackend.name);
 
     if (CodegenBackend.init_func == NULL) {
         ERROR("backend: %s is not properly initialized", CodegenBackend.name);
-        return NoBackend;
+        return new_backend_error(NoBackend);
     }
 
-    size_t code = CodegenBackend.init_func();
+    BackendError code = CodegenBackend.init_func();
 
-    if (code) {
+    if (code.kind != Success) {
         ERROR("failed to initialize backend: %s with code: %ld", CodegenBackend.name, code);
-        return Other;
+        return code;
     }
 
-    return Success;
+    return new_backend_error(Success);
 }
 
 BackendError deinit_backend(void) {
@@ -32,17 +45,17 @@ BackendError deinit_backend(void) {
 
     if (CodegenBackend.deinit_func == NULL) {
         ERROR("backend: %s is not properly initialized", CodegenBackend.name);
-        return NoBackend;
+        return new_backend_error(NoBackend);
     }
 
-    size_t code = CodegenBackend.deinit_func();
+    BackendError code = CodegenBackend.deinit_func();
 
-    if (code) {
+    if (code.kind != Success) {
         ERROR("failed to undo initialization of backend: %s with code: %ld", CodegenBackend.name, code);
-        return Other;
+        return code;
     }
 
-    return Success;
+    return new_backend_error(Success);
 }
 
 BackendError set_backend(const codegen_init init_func, const codegen_deinit deinit_func, const codegen codegen_func, const char* name) {
@@ -51,7 +64,7 @@ BackendError set_backend(const codegen_init init_func, const codegen_deinit dein
     CodegenBackend.codegen_func = codegen_func;
     CodegenBackend.name = name;
 
-    return Success;
+    return new_backend_error(Success);
 }
 
 BackendError generate_code(const AST_NODE_PTR root, void** output) {
@@ -59,14 +72,14 @@ BackendError generate_code(const AST_NODE_PTR root, void** output) {
 
     if (CodegenBackend.codegen_func == NULL) {
         ERROR("backend: %s is not properly initialized", CodegenBackend.name);
-        return NoBackend;
+        return new_backend_error(NoBackend);
     }
 
-    size_t code = CodegenBackend.codegen_func(root, output);
-    if (code) {
+    BackendError code = CodegenBackend.codegen_func(root, output);
+    if (code.kind) {
         ERROR("code generation of backend: %s failed with code: %ld", CodegenBackend.name, code);
-        return Other;
+        return code;
     }
 
-    return Success;
+    return new_backend_error(Success);
 }
diff --git a/src/codegen/backend.h b/src/codegen/backend.h
index 6e733c3..02cbc43 100644
--- a/src/codegen/backend.h
+++ b/src/codegen/backend.h
@@ -4,28 +4,42 @@
 
 #include <ast/ast.h>
 
-typedef enum BackendError_t {
+typedef struct BackendImplError_t {
+    // faulty AST node
+    AST_NODE_PTR ast_node;
+    // error message
+    const char* message;
+} BackendImplError;
+
+typedef enum BackendErrorKind_t {
     Success,
     NoBackend,
     BackendAlreadySet,
-    Other
+    Unimplemented,
+    // some error occurred in the backend implementation
+    Implementation
+} BackendErrorKind;
+
+typedef struct BackendError_t {
+    BackendErrorKind kind;
+    BackendImplError impl;
 } BackendError;
 
 /**
  * @brief Function called by the compiler backend to generate an intermediate format
  *        from AST. Returns a custom container for its intermediate language.
  */
-typedef size_t (*codegen)(const AST_NODE_PTR, void**);
+typedef BackendError (*codegen)(const AST_NODE_PTR, void**);
 
 /**
  * @brief Initialize the code generation backend.
  */
-typedef size_t (*codegen_init)(void);
+typedef BackendError (*codegen_init)(void);
 
 /**
  * @brief Undo initialization of code generation backend.
  */
-typedef size_t (*codegen_deinit)(void);
+typedef BackendError (*codegen_deinit)(void);
 
 /**
  * @brief Set the backend functions to use
@@ -65,4 +79,14 @@ BackendError deinit_backend(void);
 [[nodiscard]]
 BackendError generate_code(const AST_NODE_PTR root, void** code);
 
+/**
+ * @brief Create a new backend error
+ * 
+ * @param kind must ne != Implementation
+ * @return BackendError 
+ */
+BackendError new_backend_error(BackendErrorKind kind);
+
+BackendError new_backend_impl_error(BackendErrorKind kind, AST_NODE_PTR node, const char* message);
+
 #endif // CODEGN_BACKEND_H_
diff --git a/src/llvm/backend.c b/src/llvm/backend.c
index 2f7fc6d..6c31665 100644
--- a/src/llvm/backend.c
+++ b/src/llvm/backend.c
@@ -10,7 +10,7 @@ typedef enum LLVMBackendError_t {
     UnresolvedImport
 } LLVMBackendError;
 
-static size_t llvm_backend_codegen(const AST_NODE_PTR, void**) {
+static BackendError llvm_backend_codegen(const AST_NODE_PTR, void**) {
     // we start with a LLVM module
     LLVMContextRef context = LLVMContextCreate();
     LLVMModuleRef module = LLVMModuleCreateWithNameInContext("gemstone application", context);
@@ -20,21 +20,21 @@ static size_t llvm_backend_codegen(const AST_NODE_PTR, void**) {
     LLVMDisposeModule(module);
     LLVMContextDispose(context);
 
-    return Success;
+    return new_backend_error(Success);
 }
 
-static size_t llvm_backend_codegen_init(void) {
-    return Success;
+static BackendError llvm_backend_codegen_init(void) {
+    return new_backend_error(Success);
 }
 
-static size_t llvm_backend_codegen_deinit(void) {
-    return Success;
+static BackendError llvm_backend_codegen_deinit(void) {
+    return new_backend_error(Success);
 }
 
 void llvm_backend_init() {
     BackendError err = set_backend(&llvm_backend_codegen_init, &llvm_backend_codegen_deinit, &llvm_backend_codegen, "LLVM");
 
-    if (err != Success) {
+    if (err.kind != Success) {
         PANIC("unable to init llvm backend: %ld", err);
     }
 }
diff --git a/src/llvm/function/function.c b/src/llvm/function/function.c
new file mode 100644
index 0000000..73daecc
--- /dev/null
+++ b/src/llvm/function/function.c
@@ -0,0 +1,75 @@
+
+#include "ast/ast.h"
+#include <llvm/function/function.h>
+#include <llvm/types/type.h>
+#include <string.h>
+
+static enum IO_Qualifier_t io_qualifier_from_string(const char* str) {
+    if (strcmp(str, "in") == 0) {
+        return In;
+    }
+
+    return Out;
+}
+
+static enum IO_Qualifier_t merge_qualifier(enum IO_Qualifier_t a, enum IO_Qualifier_t b) {
+    enum IO_Qualifier_t result = Unspec;
+
+    if (a == In && b == Out) {
+        result = InOut;
+    } else if (a == Out && b == In) {
+        result = InOut;
+    }
+
+    return result;
+}
+
+static enum IO_Qualifier_t io_qualifier_from_ast_list(const AST_NODE_PTR node) {
+    // node is expected to be a list
+    if (node->kind != AST_List) {
+        PANIC("Node must be of type AST_List: %s", AST_node_to_string(node));
+    }
+
+    enum IO_Qualifier_t qualifier = Unspec;
+
+    for (size_t i = 0; i < node->child_count; i++) {
+        
+        AST_NODE_PTR qualifier_node = AST_get_node(node, i);
+
+        if (qualifier_node->kind != AST_Qualifyier) {
+            PANIC("Node must be of type AST_Qualifyier: %s", AST_node_to_string(node));
+        }
+
+        enum IO_Qualifier_t local_qualifier = io_qualifier_from_string(qualifier_node->value);
+
+        if (qualifier == Unspec) {
+            qualifier = local_qualifier;
+        } else {
+            qualifier = merge_qualifier(qualifier, local_qualifier);
+        }
+    }
+
+    if (qualifier == Unspec)
+        qualifier = In;
+
+    return qualifier;
+}
+
+GemstoneParam param_from_ast(const AST_NODE_PTR node) {
+    GemstoneParam param;
+
+    // node is expected to be a parameter
+    if (node->kind != AST_Parameter) {
+        PANIC("Node must be of type AST_ParamList: %s", AST_node_to_string(node));
+    }
+
+    AST_NODE_PTR qualifier_list = AST_get_node(node, 0);
+    param.qualifier = io_qualifier_from_ast_list(qualifier_list);
+
+    AST_NODE_PTR param_decl = AST_get_node(node, 1);
+    AST_NODE_PTR param_type = AST_get_node(param_decl, 0);
+    param.typename = get_type_from_ast(param_type);
+    param.name = AST_get_node(param_decl, 1)->value;
+
+    return param;
+}
diff --git a/src/llvm/function/function.h b/src/llvm/function/function.h
new file mode 100644
index 0000000..54df9a4
--- /dev/null
+++ b/src/llvm/function/function.h
@@ -0,0 +1,42 @@
+
+#ifndef LLVM_FUNCTION_H_
+#define LLVM_FUNCTION_H_
+
+#include <ast/ast.h>
+#include <llvm/types/type.h>
+
+enum IO_Qualifier_t {
+    Unspec,
+    In,
+    Out,
+    InOut
+};
+
+typedef struct GemstoneParam_t {
+    const char* name;
+    enum IO_Qualifier_t qualifier;
+    GemstoneType typename;
+} GemstoneParam;
+
+typedef struct GemstoneFun_t {
+    const char* name;
+    // TODO: add array of parameters
+} GemstoneFun;
+
+/**
+ * @brief Convert an AST node into a function parameter struct
+ * 
+ * @param node the node starting a function parameter
+ * @return GemstoneParam 
+ */
+GemstoneParam param_from_ast(const AST_NODE_PTR node);
+
+/**
+ * @brief Convert an AST node into a function
+ * 
+ * @param node the node starting a function
+ * @return GemstoneFun 
+ */
+GemstoneFun fun_from_ast(const AST_NODE_PTR node);
+
+#endif // LLVM_FUNCTION_H_
diff --git a/src/llvm/type.c b/src/llvm/types/composite.c
similarity index 77%
rename from src/llvm/type.c
rename to src/llvm/types/composite.c
index c1b178e..416087b 100644
--- a/src/llvm/type.c
+++ b/src/llvm/types/composite.c
@@ -1,52 +1,8 @@
 
-#include <ast/ast.h>
+#include <llvm/types/composite.h>
 #include <string.h>
-#include <sys/log.h>
-#include <llvm-c/Core.h>
-#include <llvm-c/Types.h>
 
-#define BITS_PER_BYTE 8
-
-enum Sign_t {
-    Signed,
-    Unsigned
-};
-
-enum Precision_t {
-    ATOM = 1,
-    HALF = 2,
-    SINGLE = 4,
-    DOUBLE = 8,
-    QUAD = 16,
-    OCTO = 32
-};
-
-enum Primitive_t {
-    Int,
-    Float
-};
-
-typedef struct CompositeType_t {
-    const char* name;
-    enum Sign_t sign;
-    enum Precision_t scale;
-    enum Primitive_t prim;
-} Composite;
-
-typedef struct TypeScope_t {
-    // vector of composite data types
-    Composite* composites;
-    size_t composite_len;
-    size_t composite_cap;
-} TypeScope;
-
-Composite* get_composite_type(const char* name);
-
-typedef struct CompositeType_t* COMPOSITE_REF;
-
-#define INVALID_COMPOSITE NULL
-
-LLVMTypeRef llvm_type_from_composite(LLVMContextRef context, const COMPOSITE_REF composite) {
+LLVMTypeRef llvm_type_from_composite(LLVMContextRef context, const CompositeRef composite) {
     DEBUG("converting composite to LLVM type...");
 
     LLVMTypeRef type = INVALID_COMPOSITE;
@@ -61,6 +17,7 @@ LLVMTypeRef llvm_type_from_composite(LLVMContextRef context, const COMPOSITE_REF
         switch (composite->scale) {
             case HALF:
                 type = LLVMHalfTypeInContext(context);
+                break;
             case SINGLE:
                 type = LLVMDoubleTypeInContext(context);
                 break;
@@ -89,7 +46,7 @@ double get_scale_factor(const char* keyword) {
     PANIC("invalid scale factor: %s", keyword);
 }
 
-enum Precision_t collapse_scale_list(const AST_NODE_PTR list) {
+enum Scale_t collapse_scale_list(const AST_NODE_PTR list) {
     double sum = 1.0;
 
     for (size_t i = 0; i < list->child_count; i++) {
@@ -99,7 +56,7 @@ enum Precision_t collapse_scale_list(const AST_NODE_PTR list) {
     }
 
     if (sum >= 1.0 && sum <= 32) {
-        return (enum Precision_t) sum;
+        return (enum Scale_t) sum;
     }
 
     PANIC("invalid combination of scale factors");
@@ -115,6 +72,18 @@ enum Sign_t string_to_sign(const char* keyword) {
     PANIC("invalid sign: %s", keyword);
 }
 
+static enum Primitive_t resolve_primitive(const char* typename) {
+
+    if (strcmp(typename, "int") == 0) {
+        return Int;
+    } else if (strcmp(typename, "float") == 0) {
+        return Float;
+    }
+
+    // TODO: implement lookup of ident type
+    return Int;
+}
+
 struct CompositeType_t ast_type_to_composite(AST_NODE_PTR type) {
     size_t count = type->child_count;
 
@@ -152,8 +121,7 @@ struct CompositeType_t ast_type_to_composite(AST_NODE_PTR type) {
         composite.scale = collapse_scale_list(AST_get_node(type, 0));
         composite.prim = resolve_primitive(AST_get_node(type, 2)->value);
     }
+
+    return composite;
 }
 
-void generate_builtin_types(LLVMContextRef context) {
-    
-}
diff --git a/src/llvm/types/composite.h b/src/llvm/types/composite.h
new file mode 100644
index 0000000..a8df186
--- /dev/null
+++ b/src/llvm/types/composite.h
@@ -0,0 +1,53 @@
+
+#ifndef LLVM_TYPE_H_
+#define LLVM_TYPE_H_
+
+#include <ast/ast.h>
+#include <sys/log.h>
+#include <llvm-c/Core.h>
+#include <llvm-c/Types.h>
+
+#define BITS_PER_BYTE 8
+
+enum Sign_t {
+    Signed,
+    Unsigned
+};
+
+enum Scale_t {
+    ATOM = 1,
+    HALF = 2,
+    SINGLE = 4,
+    DOUBLE = 8,
+    QUAD = 16,
+    OCTO = 32
+};
+
+enum Primitive_t {
+    Int,
+    Float
+};
+
+typedef struct CompositeType_t {
+    const char* name;
+    enum Sign_t sign;
+    enum Scale_t scale;
+    enum Primitive_t prim;
+} Composite;
+
+typedef struct TypeScope_t {
+    // vector of composite data types
+    Composite* composites;
+    size_t composite_len;
+    size_t composite_cap;
+} TypeScope;
+
+typedef struct CompositeType_t* CompositeRef;
+
+#define INVALID_COMPOSITE NULL
+
+LLVMTypeRef llvm_type_from_composite(LLVMContextRef context, const CompositeRef composite);
+
+struct CompositeType_t ast_type_to_composite(AST_NODE_PTR type);
+
+#endif // LLVM_TYPE_H_
diff --git a/src/llvm/types/type.c b/src/llvm/types/type.c
new file mode 100644
index 0000000..2b8911d
--- /dev/null
+++ b/src/llvm/types/type.c
@@ -0,0 +1,23 @@
+
+#include <llvm/types/composite.h>
+#include <ast/ast.h>
+#include <llvm/types/type.h>
+
+GemstoneType get_type_from_ast(const AST_NODE_PTR type_node) {
+    if (type_node->kind != AST_Type) {
+        PANIC("Node must be of type AST_Type: %s", AST_node_to_string(type_node));
+    }
+
+    GemstoneType type;
+
+    if (type_node->child_count > 1) {
+        // must be composite
+        type.kind = TypeComposite;
+        type.specs.composite = ast_type_to_composite(type_node);
+    } else {
+        // either custom type or box
+        // TODO: resolve concrete type from TypeScope
+    }
+
+    return type;
+}
diff --git a/src/llvm/types/type.h b/src/llvm/types/type.h
new file mode 100644
index 0000000..d7e2617
--- /dev/null
+++ b/src/llvm/types/type.h
@@ -0,0 +1,43 @@
+
+#ifndef GEMSTONE_TYPE_H_
+#define GEMSTONE_TYPE_H_
+
+#include <ast/ast.h>
+#include <llvm/types/composite.h>
+
+enum GemstoneTypeKind_t {
+    TypeComposite,
+    TypeReference,
+    TypeBox
+};
+
+struct GemstoneType_t;
+
+typedef struct GemstoneRefType_t {
+    struct GemstoneType_t* type;
+} GemstoneRefType;
+
+typedef struct GemstoneType_t {
+    enum GemstoneTypeKind_t kind;
+    union GemstoneTypeSpecs_t {
+        Composite composite;
+        GemstoneRefType reference;
+    } specs;
+} GemstoneType;
+
+struct TypeScope_t;
+
+typedef struct TypeScope_t {
+    // TODO: array of child scopes
+    // TODO: array of types
+} TypeScope;
+
+/**
+ * @brief Convert a type declaration into a concrete type.
+ * 
+ * @param type A type declaration (either identifier or composite)
+ * @return GemstoneType
+ */
+GemstoneType get_type_from_ast(const AST_NODE_PTR type);
+
+#endif // GEMSTONE_TYPE_H_
diff --git a/src/main.c b/src/main.c
index a2078bc..e9c484b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -53,6 +53,24 @@ void setup(void) {
   DEBUG("finished starting up gemstone...");
 }
 
+void run_backend_codegen() {
+  llvm_backend_init();
+
+  BackendError err;
+  err = init_backend();
+  if (err.kind != Success) {
+    return;
+  }
+
+  void* code = NULL;
+  err = generate_code(root, &code);
+  if (err.kind != Success) {
+    return;
+  }
+
+  err = deinit_backend();
+}
+
 int main(int argc, char *argv[]) {
 
   setup();
@@ -77,16 +95,9 @@ int main(int argc, char *argv[]) {
   root = AST_new_node(AST_Module, NULL);
   yyparse();
 
-  llvm_backend_init();
+  run_backend_codegen();
 
-  init_backend();
-
-  void* code = NULL;
-  generate_code(root, &code);
-
-  deinit_backend();
-
-  FILE *output = fopen("test.txt", "w");
+  FILE *output = fopen("test.gv", "w");
   AST_fprint_graphviz(output, root);
   fclose(output);
   AST_delete_node(root);