Fold Assignment
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Lexical scope is not unique to ML. Nearly all programming languages use lexical scope, including Java.
First, we will build the utility methods: foldLeft (which can be easily built with tail recursion) and foldRight (which cannot).
Next, we will build some applications which use fold: sum (which does not require lexical scope) and countBetweenMinAndMaxExclusive (which does).
Contents
Code To Implement
Fold
class: | FoldHof.java | ![]() |
methods: | foldLeft foldRight |
|
package: | hof.fold.assignment | |
source folder: | src/main/java |
foldLeft
public static <A, B> A foldLeft(BiFunction<A, B, A> f, A acc, ImmutableList<B> list)![]()
foldLeft(f, initial_value, [x1, x2, ..., xn])
- returns
f(xn,...,f(x2, f(x1, initial_value))...)
orinitial_value
if the list is empty.
foldRight
public static <A, B> A foldRight(BiFunction<A, B, A> f, A acc, ImmutableList<B> list)![]()
foldRight(f, initial_value, [x1, x2, ..., xn])
- returns
f(x1, f(x2, ..., f(xn, init)...))
orinitial_value
if the list is empty.
Fold Apps
class: | FoldHofApps.java | ![]() |
methods: | sum countBetweenMinAndMaxExclusive |
|
package: | hof.map.assignment | |
source folder: | src/main/java |
sum
public static int sum(ImmutableList<Integer> xs)
countBetweenMinAndMaxExclusive
public static int countBetweenMinAndMaxExclusive(int min, int maxExclusive, ImmutableList<Integer> xs)
Test
class: | FoldTestSuite.java | ![]() |
package: | hof.fold.assignment | |
source folder: | src/test/java |