Homework 5
due before class Oct 31, 2008
1. (20pts) Draw a snapshot of the runtime stack for the following ML code immediately
before the last call to plus returns to the body of repeat.
1 fun plus(x) = x + 1;
2 fun main(x) =
3 let val y = x + 1
4 in let fun repeat(f,x) =
5 let y = f(x)
6 in f(y)
7 end
8 in repeat(plus, y)
9 end
10 end;
11 main (5);
12
The activation record for each function needs to have a control link, an access link,
a return address, a return value address, parameters, and local variables. Remember
that function values are represented by closures and that a closure is a pair consisting
of an environment (pointer to an activation record) and compiled code. Use the line
numbers in the code to indicate the return address of each function call (the line
number immediately following the function call). Follow guidelines in lab8.
Solution:
/* "->" means "points-to"; ":" means "has value" */
/* <global, code for plus> is the closure storage for function plus*/
/* <main(5) : ?> means main(5) has an undefined value at the time*/
/* <main.main(5)> means the main(5) storage allocated in the AR of main*/
Memory layout (runtime stack):
global: {
Control Link -> NULL;
Access Link -> NULL;
local-vars--- plus -> <global, code for plus>
main -> <global, code for main>
main(5) : ?
}
main : {
1
