// expand definition formals to pairs
func ExpandFormals(nodes []ast.Node) ast.Node {
//(1).
// (define (<variable> <formals>) <body>) equivalent to
// (define <variable>
// (lambda (<formals>) <body>))
//(2).
// (define (<variable> . <formal>) <body>) equivalent to
// <formal> should be a single variable
// (define <variable>
// (lambda <formal> <body>))
prev := ast.NewPair(nil, nil)
curr := ast.NewPair(nil, nil)
front := prev
dotted := false
exists := make(map[string]bool)
for i, node := range nodes {
switch node.(type) {
case *ast.Name:
id := node.(*ast.Name).Identifier
if id == "." {
dotted = true
if i+1 == len(nodes) {
panic(fmt.Sprint("unexpected `)' after dot"))
}
} else {
if _, ok := exists[id]; ok {
panic(fmt.Sprint("duplicate argument identifier: ", node))
} else {
exists[id] = true
}
if dotted {
prev.Second = node
// should be the last element
if i+1 < len(nodes) {
panic(fmt.Sprint("illegal use of `.'"))
}
} else {
curr.First = node
prev.Second = curr
prev = curr
curr = ast.NewPair(nil, nil)
}
}
default:
panic(fmt.Sprint("illegal argument type: ", node))
}
}
return front.Second
}
func ExpandList(nodes []ast.Node) ast.Node {
prev := ast.NewPair(nil, nil)
curr := ast.NewPair(nil, nil)
front := prev
dotted := false
for i, node := range nodes {
isdot := false
expanded := node
switch node.(type) {
case *ast.Name:
id := node.(*ast.Name).Identifier
if id == "." {
isdot = true
dotted = true
if i == 0 || i+2 != len(nodes) {
panic(fmt.Sprint("illegal use of `.'"))
}
}
case *ast.Tuple:
elements := node.(*ast.Tuple).Elements
expanded = ExpandList(elements)
default:
}
if !isdot {
if dotted {
prev.Second = expanded
} else {
prev.Second = curr
curr.First = expanded
prev = curr
curr = ast.NewPair(nil, nil)
}
}
}
return front.Second
}