35 lines
1.6 KiB
Scheme
35 lines
1.6 KiB
Scheme
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(load "util.scm")
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(load "misc/evaluator.scm")
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(display "\nex-4.31 - explicit-laziness\n")
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; Exercise 4.31. The approach taken in this section is somewhat unpleasant,
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; because it makes an incompatible change to Scheme. It might be nicer to
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; implement lazy evaluation as an upward-compatible extension, that is, so that
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; ordinary Scheme programs will work as before. We can do this by extending the
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; syntax of procedure declarations to let the user control whether or not
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; arguments are to be delayed. While we're at it, we may as well also give the
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; user the choice between delaying with and without memoization. For example,
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; the definition
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;(define (f a (b lazy) c (d lazy-memo))
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; ...)
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; would define f to be a procedure of four arguments, where the first and third
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; arguments are evaluated when the procedure is called, the second argument is
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; delayed, and the fourth argument is both delayed and memoized. Thus, ordinary
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; procedure definitions will produce the same behavior as ordinary Scheme,
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; while adding the lazy-memo declaration to each parameter of every compound
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; procedure will produce the behavior of the lazy evaluator defined in this
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; section. Design and implement the changes required to produce such an
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; extension to Scheme. You will have to implement new syntax procedures to
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; handle the new syntax for define. You must also arrange for eval or apply to
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; determine when arguments are to be delayed, and to force or delay arguments
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; accordingly, and you must arrange for forcing to memoize or not, as
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; appropriate.
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; (display "\nex-4.32\n")
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; (display "\nex-4.33\n")
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; (display "\nex-4.34\n")
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