Plan 9's rc.
not a clear win over byron's,
but at least it has the right syntax.
diff --git a/src/cmd/rc/tree.c b/src/cmd/rc/tree.c
new file mode 100644
index 0000000..9bf76d8
--- /dev/null
+++ b/src/cmd/rc/tree.c
@@ -0,0 +1,114 @@
+#include "rc.h"
+#include "exec.h"
+#include "io.h"
+#include "fns.h"
+tree *treenodes;
+/*
+ * create and clear a new tree node, and add it
+ * to the node list.
+ */
+tree *newtree(void){
+ tree *t=new(tree);
+ t->iskw=0;
+ t->str=0;
+ t->child[0]=t->child[1]=t->child[2]=0;
+ t->next=treenodes;
+ treenodes=t;
+ return t;
+}
+void freenodes(void){
+ tree *t, *u;
+ for(t=treenodes;t;t=u){
+ u=t->next;
+ if(t->str) efree(t->str);
+ efree((char *)t);
+ }
+ treenodes=0;
+}
+tree *tree1(int type, tree *c0)
+{
+ return tree3(type, c0, (tree *)0, (tree *)0);
+}
+tree *tree2(int type, tree *c0, tree *c1)
+{
+ return tree3(type, c0, c1, (tree *)0);
+}
+tree *tree3(int type, tree *c0, tree *c1, tree *c2)
+{
+ tree *t;
+ if(type==';'){
+ if(c0==0) return c1;
+ if(c1==0) return c0;
+ }
+ t=newtree();
+ t->type=type;
+ t->child[0]=c0;
+ t->child[1]=c1;
+ t->child[2]=c2;
+ return t;
+}
+tree *mung1(tree *t, tree *c0)
+{
+ t->child[0]=c0;
+ return t;
+}
+tree *mung2(tree *t, tree *c0, tree *c1)
+{
+ t->child[0]=c0;
+ t->child[1]=c1;
+ return t;
+}
+tree *mung3(tree *t, tree *c0, tree *c1, tree *c2)
+{
+ t->child[0]=c0;
+ t->child[1]=c1;
+ t->child[2]=c2;
+ return t;
+}
+tree *epimung(tree *comp, tree *epi)
+{
+ tree *p;
+ if(epi==0) return comp;
+ for(p=epi;p->child[1];p=p->child[1]);
+ p->child[1]=comp;
+ return epi;
+}
+/*
+ * Add a SIMPLE node at the root of t and percolate all the redirections
+ * up to the root.
+ */
+tree *simplemung(tree *t)
+{
+ tree *u;
+ struct io *s;
+ t=tree1(SIMPLE, t);
+ s=openstr();
+ pfmt(s, "%t", t);
+ t->str=strdup(s->strp);
+ closeio(s);
+ for(u=t->child[0];u->type==ARGLIST;u=u->child[0]){
+ if(u->child[1]->type==DUP
+ || u->child[1]->type==REDIR){
+ u->child[1]->child[1]=t;
+ t=u->child[1];
+ u->child[1]=0;
+ }
+ }
+ return t;
+}
+tree *token(char *str, int type)
+{
+ tree *t=newtree();
+ t->type=type;
+ t->str=strdup(str);
+ return t;
+}
+void freetree(tree *p)
+{
+ if(p==0) return;
+ freetree(p->child[0]);
+ freetree(p->child[1]);
+ freetree(p->child[2]);
+ if(p->str) efree(p->str);
+ efree((char *)p);
+}
