Performance and Evaluation of Lisp Systems - Dreamsongs

3.3 Ctak
CTAK is a variant of TAK that uses CATCH and THROW to return values
rather than the function-return mechanism. Not all Lisps have CATCH/THROW
functionality; INTERLISP can mimic the behavior of CATCH/THROW with its
much more powerful spaghetti stack. The times for INTERLISP on this benchmark
are quite slow, but the implementation doubles the number of function calls, as
we shall see.
3.3.1 The Program
(defun ctak (x y z)
(catch ’ctak (ctak-aux x y z)))
(defun ctak-aux (x y z)
(cond ((not (< y x))
(throw ’ctak z))
(t (ctak-aux
(catch ’ctak
(ctak-aux (1- x)
y
z))
(catch ’ctak
(ctak-aux (1- y)
z
x))
(catch ’ctak
(ctak-aux (1- z)
x
y))))))
3.3.2 Analysis
This benchmark is similar to TAK, but has both CATCH and THROW. The
use of CATCH and THROW here is somewhat trivial because the THROW always
throws to the nearest enclosing CATCH frame. Typically, CATCH and THROW
are implemented in the following manner: whenever a CATCH is evaluated, a
catch frame is placed on the stack. In the catch frame is a pointer to the next
enclosing catch frame, so that we end up with a linked list of catch frames. When
a THROW is evaluated, it determines which tag it will search for, and it will
search up this threaded list of catch frames, checking whether the tags are EQ. In
CTAK, this search only goes as far as the first catch frame. The length of time
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