macro: macros seem to work

macro/macro.go

@@ -45,12 +45,73 @@ func handleMac(l []*ast.AST, m MacroEnv) (*ast.AST, error) {
 		params = append(params, elem.Val.(string))
 	}
 
-	m[name] = Macro{params, l[2]}
+	m[name] = Macro{params, l[3]}
 
 	nilVal := ast.AST{ast.Symbol, "nil"}
 	return &nilVal, nil
 }
 
+func transformList(l []*ast.AST, args map[string]*ast.AST) (*ast.AST, error) {
+	var res []*ast.AST
+
+	for _, elem := range l {
+		transformed, err := doTransform(elem, args)
+
+		if err != nil {
+			return nil, err
+		}
+
+		res = append(res, transformed)
+	}
+
+	lst := ast.AST{ast.List, res}
+
+	return &lst, nil
+}
+
+func doTransform(transformer *ast.AST, args map[string]*ast.AST) (*ast.AST, error) {
+	switch transformer.Tag {
+	case ast.List:
+		lst := transformer.Val.([]*ast.AST)
+		if len(lst) > 0 && lst[0].Tag == ast.Symbol && lst[0].Val.(string) == "list" {
+			return transformList(lst[1:], args)
+		}
+		if len(lst) > 0 && lst[0].Tag == ast.Symbol && lst[0].Val.(string) == "quote" {
+			return lst[1], nil
+		}
+		return transformer, nil
+	case ast.Quoted:
+		return transformer.Val.(*ast.AST), nil
+	case ast.Symbol:
+		key := transformer.Val.(string)
+		val, ok := args[key]
+		if !ok {
+			return nil, fmt.Errorf("Unbound symbol %s", key)
+		}
+		return val, nil
+	}
+	return transformer, nil
+}
+
+func transform(l *ast.AST, macro Macro, m MacroEnv) (*ast.AST, error) {
+	args := make(map[string]*ast.AST)
+	vals := l.Val.([]*ast.AST)[1:]
+
+	if len(vals) != len(macro.params) {
+		return nil, fmt.Errorf("Wrong number of arguments to macro")
+	}
+
+	for i, arg := range vals {
+		expanded, err := Expand(arg, m)
+		if err != nil {
+			return nil, err
+		}
+		args[macro.params[i]] = expanded
+	}
+
+	return doTransform(macro.transformer, args)
+}
+
 func traverse(l *ast.AST, m MacroEnv) (*ast.AST, error) {
 	vals := l.Val.([]*ast.AST)
 	if len(vals) == 0 {
@@ -61,6 +122,16 @@ func traverse(l *ast.AST, m MacroEnv) (*ast.AST, error) {
 		return handleMac(vals, m)
 	}
 
+	if vals[0].Tag == ast.Symbol {
+		sym := vals[0].Val.(string)
+
+		macro, ok := m[sym]
+
+		if ok {
+			return transform(l, macro, m)
+		}
+	}
+
 	return l, nil
 }