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 Prayer beads - Lindsey Kuper [entries|archive|friends|userinfo]
Lindsey Kuper

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Prayer beads [Sep. 26th, 2008|01:55 pm]
Lindsey Kuper
 [ Tags | b521 ]

Lindsey: So, um, I have a confession to make.
Will: Okay.
Lindsey: Uh, I might have cheated. I was working on the "write-`factorial`-without-using-`define`-or-`letrec`" problem, and I thought, "Huh, maybe this is that crazy Y-combinator thing that everyone's always talking about." And I pretty much found, um, almost exactly the code we were supposed to write.
Lindsey: No! Give me some credit! What I did was look up 'Y operator' in the index of SICP.
Lindsey: Wait! Don't be mad! To atone for my sins, I did the exercise that they want you to do, which is to do the analogous thing for computing Fibonacci numbers. And I understand it, I really do!
Will: Fine. Then do it for factorial, on the board, right now.
Lindsey: *turns pale*
Will: Here's the chalk.
Lindsey: Um. Okay, so this section of board here is my scratch paper. *starts to write some stuff on the board*
Will: No, no, no. Forget you ever heard of the Y combinator. I want you to start with regular, boring, first-day-of-class `factorial` and derive it from that, step by step.
Lindsey: Hmm. *starts over on another section of the board*
Ramana: *walks in; notices what I had been writing earlier* Who wrote that?
Will: Nobody.
Lindsey: Nobody.
Will: Actually, Sussman and Abelson wrote it.
Lindsey: *has to forcibly restrain self from making an obscene gesture at Will*

Twenty minutes later, with lots of help, I've figured out how to derive the self-application thing, and I'm like "I should go work on the next problem." And they're like "You better not look at SICP for that one."