CSE 3302 Programming LanguagesGradingLetter GradesWhat’s aheadGrades on WebCTFoldl and FoldrSlide 7Slide 8Lambda ExpressionsWhy Are Lambda's Useful?Another exampleExercisesSlide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21CSE 3302 Programming LanguagesChengkai LiSpring 2008Functional Programming Language: Haskell (cont’d)Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20081Grading•Homework (HW): 25%. (HW1, HW2, HW3, HW4, HW5)•Machine Problems (MP): 20%. (MP1, MP2)•Essays (ES): 10%. •Midterm exam: 20%. •Final exam: 25%. •Bonus points: 5%. Based on class participation. some additional bonus points (in MP2, HW5)Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20082Letter Grades•curve-based•The cutoffs for letter grades are based on your performance.•Bonus point: can only increase your gradeExample: cutoff for A: 88.5your raw score: 86bonus points: 3your grade: B -> A (86+3>88.5)Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20083What’s ahead•HW4: due by April 21st•HW5: due by May 2nd•Essay: have you started yet? (due at May 1st)Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20084Grades on WebCTLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20085Foldl and Foldrfoldl :: (a -> b -> a) -> a -> [b] -> afoldl f z [] = zfoldl f z (x:xs) = foldl f (f z x) xsfoldr :: (a -> b -> b) -> b -> [a] -> bfoldr f z [] = zfoldr f z (x:xs) = f x (foldr f z xs)Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20086Foldr: is right-associativeFoldl: is left-associativeLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20087foldr (-) 1 [2,3,4]foldl (-) 1 [2,3,4](section 3.3.2 in the tutorial)Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20088foldr v [x0,x1, …, xn] = x0 (x1 (…(xn v)…)) foldl v [x0,x1, …, xn] = (…((v x0) x1)…) xnLambda ExpressionsA function can be constructed without giving it a name by using a lambda expression.\x -> x+1The nameless function that takes a number x and returns the result x+1.Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 20089Why Are Lambda's Useful?Lambda expressions can be used to give a formal meaning to functions defined using currying.For example:add x y = x+yadd = \x -> (\y -> x+y)meansLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200810Another examplemeansLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200811compose f g x = f (g x)compose f g = \x -> f (g x)Exercises1. Write a recursive function sum n that returns 1 + 2 + …. + nLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200812Exercises2. Write a recursive function genlist n that returns [ 1, 2, …, n ].Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200813Exercises2. (cont.) Check to make sure n>0, otherwise return empty list.Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200814Exercises3.Check if an element is a member of a list.Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200815Exercises4.Implement ++Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200816Exercises4. (cont.) Merge two lists and return a list with elements sortedLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200817Exercises5. A triple (x,y,z) of positive integers is pythagorean if x^2+y^2=z^2. Using list comprehension to define a function pyths::Int->[(Int, Int, Int)] that returns the list of all pythagorean triples whose components are at most a given limit. For example:>pyths 10[(3,4,5), (4,3,5), (6,8,10), (8,6,10)]Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200818Exercises5. (cont.) Make sure x <= y <= zLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200819Exercises6. Define list comprehension [ f x | x <- xs, p x] using map and filter.Lecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li, 200820Exercises7. Define map f and filter p using foldrLecture 20 – Functional Programming, Spring 2008CSE3302 Programming Languages, UT-Arlington ©Chengkai Li,
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