Package io.atlassian.fugue.law

Class SemigroupLaws<A>

  • public final class SemigroupLaws<A>
extends java.lang.Object
    Laws for a semigroup

    • Field Detail

    • Constructor Detail

      • SemigroupLaws

        public SemigroupLaws​(Semigroup<A> semigroup)
        Build a law instance to check semigroup properties
        Parameters:
        semigroup - a Semigroup to check matches the desired behaviors of

    • Method Detail

      • semigroupAssociative

        public IsEq<A> semigroupAssociative​(A x,
                                    A y,
                                    A z)
        A semigroup must not care about the order elements are combined. If you combine x with y and then with z the result should be the same as combining y with z and then with x.
        Parameters:
        x - an A object
        y - an A object
        z - an A object
        Returns:
        a IsEq instance where append(append(x,y),z) is equal to append(x, append(y,z))

      • sumNonEmptyEqualFold

        public IsEq<A> sumNonEmptyEqualFold​(A head,
                                    java.lang.Iterable<A> tail)
        The Semigroup.sumNonEmpty(Object, Iterable) function of your semigroup must be equal to a Functions.fold(BiFunction, Object, Iterable) where append is used as the combining function, head is used as the initial value and tail is the iterable to check
        Parameters:
        head - an A
        tail - a Iterable of A's
        Returns:
        a IsEq where sumeNonEmpty(head, tail) is equal to fold(append, head, tail)

      • multiply1pEqualRepeatedAppend

        public IsEq<A> multiply1pEqualRepeatedAppend​(int n,
                                             A a)
        The Semigroup.multiply1p(int, Object) function of your semigroup must be equal to Semigroup.sumNonEmpty(Object, Iterable) applied to the input and an iterable containing n - 1 copies of that input
        Parameters:
        n - a int representing the number of copies of the input to combine
        a - an A
        Returns:
        a IsEq where multiply(n,a) is equal to sumNonEmpty(a, take(n-1, cycle(a))