lab7 - The second problem is that the value remembered in...

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CS 61A Week 7 solutions LAB: 1. Add REPEAT to person class. (define-class (person name) (INSTANCE-VARS (OLD-TEXT '())) (method (say stuff) (SET! OLD-TEXT STUFF) stuff) (method (ask stuff) (ask self 'say (se '(would you please) stuff))) (method (greet) (ask self 'say (se '(hello my name is) name))) (METHOD (REPEAT) OLD-TEXT)) Notice that the ASK and GREET methods don't have to set old-text, because they use the SAY method. 2. Which double-talkers work? (define-class (double-talker name) (parent (person name)) (method (say stuff) (se (usual 'say stuff) (ask self 'repeat))) ) There are two things wrong with this approach. One is that it assumes that the two arguments to SE are evaluated left-to-right, since the use of REPEAT assumes that we've just said the new stuff. That might work in some versions of Scheme but not in others.
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Unformatted text preview: The second problem is that the value remembered in old-text will be a single copy of the argument, rather than two copies; therefore, if we ask this double-talker to repeat, it'll only say the thing once. (define-class (double-talker name) (parent (person name)) (method (say stuff) (se stuff stuff)) ) This would work except for the REPEAT feature. We can ask a double-talker to ASK or to GREET and it will correctly say the right thing twice. But if we ask this double-talker to REPEAT, it won't say anything at all, because it never remembered the stuff in old-text. (define-class (double-talker name) (parent (person name)) (method (say stuff) (usual 'say (se stuff stuff))) ) This one works as desired....
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This note was uploaded on 05/12/2010 for the course CS 61A taught by Professor Harvey during the Spring '08 term at Berkeley.

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