lecture3

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Click to edit Master subtitle style 2/19/10 Class 3: Rules of Evaluati on David Evans cs1120 Fall 2009
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2/19/10 Menu Questions from Notes Computing photomosaics, non-recursive languages, hardest language elements to learn Scheme’s Rules of Evaluation (break: Survey Responses) 22
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2/19/10 If it takes 60 seconds to compute a photomosaic for Problem Set 1 today on a typical PC, estimate how long it will take cs1120 students in 2012 to compute the same photomosaic? How long will it take in 2015? > (/ (* (- 2012 2009) 12) 18) 2 > (/ 60 (* 2 2)) 15 > (/ (* (- 2015 2009) 12) 18) 4 > (/ 60 (* 2 2 2 2)) 15/4 > (exact->inexact (/ 60 (* 2 2 2 2))) 3.75 Difference in years * 12 = number of months Number of months / 18 = number of doublings according to Moore’s Law 60 seconds today, 2 doublings by 2012 15 seconds in 2012 60 seconds today, 4 doublings by 2015 3.75 seconds in 2015 Reality check: Moore’s “law” is just an “observation”. 33
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2/19/10 Are there any non-recursive natural languages? What would happen to a society that spoke one? Not for humans at least. They would run out of original things to say. Chimps and Dolphins are able to learn non-recursive “languages”, but only humans have learned recursive languages . 44
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2/19/10 Running out of Ideas “Its all been said before.” Eventually true for a non-recursive language. Never true for a recursive language. There is always something original left to say! 55
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2/19/10 Language Elements When learning a foreign language, which elements are Primitives: lots of them, and hard to learn real meaning Means of Combination Complex, but, all natural languages have similar ones [Chomsky] SOV (45% of all languages) Sentence ::= Subject Object Verb (Korean) SVO (42%) Sentence ::= Subject Verb Object (English) VSO (9%) Sentence ::= Verb Subject Object (Welsh) “Lladdodd y ddraig y dyn.” (Killed the dragon the man.) OSV (<1%): Tobati (New Guinea) Scheme: Means of Abstraction: few of these, but tricky to learn Expression ::= ( Verb Object ) defin e 66
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Pages in Revised5 Report on the Algorithmic Language Scheme Primitives Means of Combinati on Means of Abstractio n 48 pages total (includes formal specification and examples)
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Pages in Revised5 Report on the Algorithmic Language Scheme Primitives Standard Procedures Primitive expressions Identifiers, numerals 18 2 1 Means of Combinati on Expressions Program structure 2 2 Means of Abstractio n Definition s ½ 48 pages total (includes formal
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Pages in Revised5 Report on the Algorithmic Language Scheme Pages in C++ Language
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lecture3 - Click to edit Master subtitle style Class 3:...

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