Consider the recursion example distributed on Feb. $20$:

TITLE "Tree demo with traversal"

USE "hawk.h$"$

USE "stdio.h$"$

; displacements into the record structure of a tree node

LEFT $=0$ ; children

RIGHT $=4$

VALUE $=8$ ; integer value of this node

NODESIZE$=12$

; tool for statically construct tree nodes

MACRO TREENODE left,right,value

W left

W right

W value

ENDMAC

; a tree to traverse

N$1$: TREENODE NULL,NULL,$1$

N$2$: TREENODE N$1,$NULL,$2$

N$3$: TREENODE N$2,$N$5,3$

N$4$: TREENODE NULL,NULL,$4$

N$5$: TREENODE N$4,$N$6,5$

N$6$: TREENODE NULL,NULL,$6$

ROOT $=$ N$3$

SUBTITLE "traverse $--$ recursive tree traversal"

; traverse$($ root $)--$ does an inorder traversal, printing each node's value

; AR for traverse

RETAD $=0$

NODE $=4$

ARSIZE $=8$

TRAVERSE:

; expects: r$3=$ root tree or subtree to traverse

STORES R$1,$R$2$

STORE R$3,$R$2,$NODE ; node $=$ parameter

ADDSI R$2,$ARSIZE

TESTR R$3$

BZS TRAVQT ; if $($node $!=$ null$)\{$

LOAD R$3,$R$3,$LEFT ; $--$ parameter

JSR R$1,$TRAVERSE ; traverse$($ node$->$left $)$

LOAD R$3,$R$2,$NODE$-$ARSIZE

LOAD R$3,$R$3,$VALUE ; $--$ parameter

LIS R$4,3$ ; $--$ parameter

LIL R$1,$PUTDEC

JSRS R$1,$R$1$ ; putdec$($ node$->$value, $3)$

LOAD R$3,$R$2,$NODE$-$ARSIZE

LOAD R$3,$R$3,$RIGHT ; $--$ parameter

JSR R$1,$TRAVERSE ; traverse$($ node$->$right $)$

TRAVQT: ; $\}$

ADDSI R$2,-$ARSIZE

LOADS PC$,$R$2$

SUBTITLE "main program"

INT MAIN

S MAIN

; AR for main

RETAD $=0$

ARSIZE $=4$

MAIN:

STORES R$1,$R$2$

ADDSI R$2,$ARSIZE

LEA R$3,$ROOT ; $--$ param

JSR R$1,$TRAVERSE ; call traverse$($ root $)$

ADDSI R$2,-$ARSIZE

LOADS PC$,$R$2$

END

The code LOAD R$3,$R$3,$RIGHT could have been replaced with $...$

A$.$ LIL R$3,$RIGHT

LOADS R$3,$R$3$

B$.$ LEA R$3,$RIGHT

LOADS R$3,$R$3$

C$.$ LEA R$3,$R$3,$RIGHT

D$.$ ADDSI R$3,$RIGHT

LOADS R$3,$R$3$