Quiz 3b Practice Questions + Answers CIS 352: Programming Languages
Question 1 (8 points).Suppose we have the following definitions in the version of our defined language that
includes exceptions.
define f = proc (n) if zero?(sub1(n)) then 50 else raise n
define h1 = proc (y) +(y,100)
define h2 = proc (z) +(z,500)
define h3 = proc (g) proc (w) +((g w), w)
Give the values for each of the following expressions:
(a) try *(10, raise 7) catch h1
Answer: 107.
try *(10, raise 7) catch h1 ;(h1 7) ;+(100,7) ;107
(b) +(12,try (f 7) catch proc (w) *(w,1000))
Answer: 7012.
Note: fapplied to an number n6=1 does a (raise n). So,
+(12,try (f 7) catch proc (w) *(w,1000)) ;+(12, (proc (w) *(w,1000) 7))
;+(12, 7000) ;7012
(c) try +(try (f 1) catch h1, 1000) catch h2
An answer. 1050.
Note: fapplied to 1 returns 50. So,
try +(try (f 1) catch h1, 1000) catch h2 ;try +(50, 1000) catch h2 ;1050
(d) try ((h3 f) 99) catch h2
An answer. 599
Note that h3 is a curried procedure. So: ((h3 f) 99) ;+((f 99),99) ;raise 99.
Thus: try ((h3 f) 99) catch h2 ;(h2 99) ;+(99,500) ;599
Question 2 (12 points).For this question we take our continuation-passing interpreter and add while-expressions
which have the following concrete and abstract syntax.
hexpi::=while hexpido hexpi
while-exp (test body)
The intended meaning of “while test do body” is to:
1. Evaluate test. (Call the resulting value t.)
2. If t=#f, then (the loop terminates) and the while-expression returns the value 37.
20.If t=#t, then
(i) evaluate body then
(ii) re-evaluate (while-exp test body).
Page 1 of 2 April 28, 2009
