parse: Always use *ListNode for Term's

eval/eval.go

@@ -45,8 +45,7 @@ func evalFactor(n *parse.FactorNode) ([]string, error) {
 	}
 }
 
-func evalTerm(n_ parse.Node) ([]string, error) {
-	n := n_.(*parse.ListNode)
+func evalTerm(n *parse.ListNode) ([]string, error) {
 	words := make([]string, 0, len(n.Nodes))
 	words = append(words, "")
 	for _, m := range n.Nodes {
@@ -75,7 +74,7 @@ func evalTerm(n_ parse.Node) ([]string, error) {
 func evalTermList(ln *parse.ListNode) ([]string, error) {
 	words := make([]string, 0, len(ln.Nodes))
 	for _, n := range ln.Nodes {
-		a, e := evalTerm(n)
+		a, e := evalTerm(n.(*parse.ListNode))
 		if e != nil {
 			return nil, e
 		}

parse/node.go

@@ -89,6 +89,8 @@ func newCommand(pos Pos) *CommandNode {
 	return &CommandNode{ListNode: *newList(pos)}
 }
 
+// A Term is represented by a ListNode of *FactorNode's.
+
 // FactorNode represents a Factor. The embedded Node is either *ListNode or
 // *StringNode.
 type FactorNode struct {

parse/parse.go

@@ -257,7 +257,7 @@ loop:
 }
 
 // Term = Factor { Factor }
-func (t *Tree) term() Node {
+func (t *Tree) term() *ListNode {
 	term := newList(t.peek().Pos)
 	term.append(t.factor())
 loop:

parse/redir.go

@@ -41,9 +41,9 @@ func newCloseRedir(fd uintptr) *CloseRedir {
 type FilenameRedir struct {
 	redir
 	Flag int
-	Filename Node
+	Filename *ListNode // a Term
 }
 
-func newFilenameRedir(fd uintptr, flag int, filename Node) *FilenameRedir {
+func newFilenameRedir(fd uintptr, flag int, filename *ListNode) *FilenameRedir {
 	return &FilenameRedir{redir{fd}, flag, filename}
 }