code builder initial

src/builder/code.rs

@@ -177,6 +177,40 @@ impl<F> SignaturesBuilder<F> where F: Invoke<SignatureBindings> {
     }
 }
 
+pub struct FunctionDefinition {
+    pub signature: Signature,
+    pub code: elements::FuncBody,
+}
+
+impl Default for FunctionDefinition {
+    fn default() -> Self {
+        FunctionDefinition {
+            signature: Signature::TypeReference(0),
+            code: elements::FuncBody::empty(),
+        }
+    }
+}
+
+pub struct FunctionBuilder<F=Identity> {
+    callback: F,
+    code: FunctionDefinition,
+}
+
+impl FunctionBuilder {
+    pub fn new() -> Self {
+        FunctionBuilder::with_callback(Identity)
+    }
+}
+
+impl<F> FunctionBuilder<F> where F: Invoke<FunctionDefinition> {
+    pub fn with_callback(callback: F) -> Self {
+        FunctionBuilder {
+            callback: callback,
+            code: Default::default(),
+        }
+    }
+}
+
 /// New function builder.
 pub fn signatures() -> SignaturesBuilder {
     SignaturesBuilder::new()

src/elements/func.rs

@@ -68,6 +68,11 @@ impl FuncBody {
         FuncBody { locals: locals, opcodes: opcodes }
     }
 
+    /// List of individual opcodes
+    pub fn empty() -> Self {
+        FuncBody { locals: Vec::new(), opcodes: Opcodes::empty() }        
+    }
+
     /// Locals declared in function body.
     pub fn locals(&self) -> &[Local] { &self.locals }
 

src/elements/ops.rs

@@ -15,6 +15,11 @@ impl Opcodes {
         Opcodes(elements)
     }
 
+    /// Empty expression with only `Opcode::End` opcode
+    pub fn empty() -> Self {
+        Opcodes(vec![Opcode::End])
+    }    
+
     /// List of individual opcodes
     pub fn elements(&self) -> &[Opcode] { &self.0 }
 }