Compiler Construction
Explain a possible implementation method for Java-style or ML-style exceptions
and handlers. [8 marks]
Consider a simple arithmetic expression e of abstract syntax:
e ::= x | n | e + e
0
| e − e
0
| e ∗ e
0
| e/e0
| −e
where x ranges over a set of (global) variables, addressable by name, and n
ranges over integer constants. Write a procedure in pseudo-code or a language
of your choice which takes an expression e and prints (one-per-line) stack-machine
instructions of the form
pushvar x
pushnum n
add ; pop two items and push their sum
sub ; pop two items and push their difference
mul ; pop two items and push their product
div ; pop two items and push their quotient
neg ; replace top item with its negation
which, when executed, have the net effect of pushing just the value of e onto the
stack. Each line of code emitted should contain a comment giving the number of
items on the stack after its execution, thus the first push and the last instruction
would both be commented with “1 item”. [12 marks]