[Haskell-cafe] ANN: signed-multiset-0.1

Stefan Holdermans stefan at vectorfabrics.com
Wed Apr 18 06:26:50 CEST 2012

I am pleased to announce the first release of signed-multiset, which implements an abstract datatype for multisets with negative membership.

The package can be obtained from


As always, feedback is welcome.




Multisets (or bags) are sets in which elements may occur more than once.
The number of times an element occurs in a multiset is called its

This package provides an efficient implementation of so-called
signed multisets, which generalise multisets by allowing for
negative membership.
That is, elements in a signed multiset can have negative multiplicities.

See also: Wayne D. Blizard. Negative membership.
Notre Dame Journal of Formal Logic/, 31(3):346--368, 1990.

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