lecture 03 -- Recursive Procedures - Copy

# lecture 03 -- Recursive Procedures - Copy - A more complex...

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10/19/2010 1 T. METIN SEZGIN OCT 11 2010 Lecture 3 Auxiliary Procedures Variables Implement occurs-free? Such that The rules of occurs-free? How do we go about the implementation? How do we go about the implementation? The grammar The procedure What do we do with occurs-free? What good is it? Any ideas of sample scenarios for occurs-free? How about application expressions? (E 1 E 2 ) ((lambda (x) (* x x)) 5) Only if we had a way of substituting values

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10/19/2010 2 subst How do we go about the implementation? How do we go about the implementation? The grammar The procedure How do we go about the implementation? The grammar The procedure How do we go about the implementation? The grammar The procedure How do we go about the implementation? The grammar The procedure
10/19/2010 3 Things to note The procedures are mutually recursive The trick of decomposing procedures for each syntactic type is important Simplifies our design Take home message Follow the Grammar

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Unformatted text preview: A more complex example  Consider the procedure number-elements  This procedure should take a list (v v 1 v 2 …) and return ( (0 v ) (1 v 1 ) …)) .  Remember the grammar  The problem  No obvious way to build (number-elements lst) from (number-elements (cdr lst))  The solution  Implement something more general  Implement number-elements-from number-elements-from  How are the arguments different?  What purpose do they serve?  Input list  Context argument (inherited attribute) The take home message Follow the grammar When following the grammar doesn’t help… Generalize Another example  Consider list-sum  How about vector sum?  You can’t take cdr of vectors! 10/19/2010 4 How do we go about the implementation? Follow the grammar When following the grammar doesn’t help… Generalize vector-sum Problem set 0  EOPL Exercises  1.1, 1.4, 1.6, 1.12, 1.21, 1.26, 1.34, 1.36...
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lecture 03 -- Recursive Procedures - Copy - A more complex...

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