{-# LANGUAGE NoImplicitPrelude #-} ----------------------------------------------------------------------------- -- | -- Module : Math.Combinatorics.Species.Class -- Copyright : (c) Brent Yorgey 2010 -- License : BSD-style (see LICENSE) -- Maintainer : byorgey@cis.upenn.edu -- Stability : experimental -- -- The Species type class, which defines a small DSL for describing -- combinatorial species. Other modules in this library provide -- specific instances which allow computing various properties of -- combinatorial species. -- ----------------------------------------------------------------------------- module Math.Combinatorics.Species.Class ( -- * The Species type class Species(..) -- * Convenience methods , oneHole , x -- ** Plurals -- | It can be grammatically convenient to define plural -- versions of species as synonyms for the singular versions. -- For example, we can use @'set' ``o`` 'nonEmpty' 'sets'@ -- instead of @'set' ``o`` 'nonEmpty' 'set'@. , sets , cycles , linOrds , subsets , ksubsets , elements -- * Derived operations -- $derived_ops , pointed -- * Derived species -- $derived , octopus, octopi , partition, partitions , permutation, permutations , ballot, ballots , simpleGraph, simpleGraphs , directedGraph, directedGraphs ) where import qualified Algebra.Differential as Differential import NumericPrelude import PreludeBase hiding (cycle) import Math.Combinatorics.Species.AST -- | The Species type class. Note that the @Differential@ constraint -- requires s to be a differentiable ring, which means that every -- instance must also implement instances for "Algebra.Additive" -- (the species 0 and species addition, i.e. disjoint sum), -- "Algebra.Ring" (the species 1 and species multiplication, -- i.e. partitional product), and "Algebra.Differential" (species -- differentiation, i.e. adjoining a distinguished element). -- -- Minimal complete definition: 'singleton', 'set', 'cycle', 'o', -- '><', '@@', 'ofSize'. -- -- Note that the 'o' operation can be used infix to suggest common -- notation for composition, and also to be read as an abbreviation -- for \"of\", as in \"top o' the mornin'\": @set \`o\` nonEmpty -- sets@. class (Differential.C s) => Species s where -- | The species @X@ of singletons. Puts a singleton structure on an -- underlying label set of size 1, and no structures on any other -- underlying label sets. 'x' is also provided as a synonym. singleton :: s -- | The species @E@ of sets. Puts a singleton structure on /any/ -- underlying label set. set :: s -- | The species @C@ of cyclical orderings (cycles/rings). cycle :: s -- | The species @L@ of linear orderings (lists). Since linear -- orderings are isomorphic to cyclic orderings with a hole, we -- may take @'linOrd' = 'oneHole' 'cycle'@ as the default -- implementation; 'linOrd' is included in the 'Species' class so it -- can be special-cased for enumeration. linOrd :: s linOrd = oneHole cycle -- | The species @p@ of subsets is given by @'subset' = 'set' * -- 'set'@. 'subset' is included in the 'Species' class so it can -- be overridden when enumerating structures: by default the -- enumeration code would generate a pair of the subset and its -- complement, but normally when thinking about subsets we only -- want to see the elements in the subset. To explicitly -- enumerate subset/complement pairs, you can use @'set' * 'set'@ -- directly. subset :: s subset = set * set -- | Subsets of size exactly k, @'ksubset' k = ('set' -- ``ofSizeExactly`` k) * 'set'@. Included with a default definition -- in the 'Species' class for the same reason as 'subset'. ksubset :: Integer -> s ksubset k = (set `ofSizeExactly` k) * set -- | Structures of the species @e@ of elements are just elements of -- the underlying set, @'element' = 'singleton' * 'set'@. Included -- with a default definition in 'Species' class for the same -- reason as 'subset' and 'ksubset'. element :: s element = singleton * set -- | Partitional composition. To form all @(f ``o`` g)@-structures on -- the underlying label set U, first form all set partitions of U; -- for each partition @p@, put an @f@-structure on the classes of -- @p@, and a separate @g@-structure on the elements in each -- class. o :: s -> s -> s -- | Cartisian product of two species. An @(f '><' g)@-structure -- consists of an @f@-structure superimposed on a @g@-structure over -- the same underlying set. (><) :: s -> s -> s -- | Functor composition of two species. An @(f '@@' g)@-structure -- consists of an @f@-structure on the set of all @g@-structures. (@@) :: s -> s -> s -- | Only put a structure on underlying sets whose size satisfies -- the predicate. ofSize :: s -> (Integer -> Bool) -> s -- | Only put a structure on underlying sets of the given size. A -- default implementation of @ofSize (==k)@ is provided, but this -- method is included in the 'Species' class as a special case -- since it can be more efficient: we get to turn infinite lists -- of coefficients into finite ones. ofSizeExactly :: s -> Integer -> s ofSizeExactly s n = s `ofSize` (==n) -- | Don't put a structure on the empty set. The default definition -- uses 'ofSize'; included in the 'Species' class so it can be -- overriden in special cases (such as when reifying species -- expressions). nonEmpty :: s -> s nonEmpty = flip ofSize (>0) -- | 'rec f' is the least fixpoint of (the interpretation of) the -- higher-order species constructor 'f'. rec :: ASTFunctor f => f -> s -- | Omega is the pseudo-species which only puts a structure on -- infinite label sets. Of course this is not really a species, -- but it is sometimes a convenient fiction to use Omega to stand -- in for recursive occurrences of a species. omega :: s -- | A convenient synonym for differentiation. @'oneHole' -- f@-structures look like @f@-structures on a set formed by adjoining -- a distinguished \"hole\" element to the underlying set. oneHole :: (Species s) => s -> s oneHole = Differential.differentiate -- | A synonym for 'singleton'. x :: Species s => s x = singleton sets :: Species s => s sets = set cycles :: Species s => s cycles = cycle -- $derived_ops -- Some derived operations on species. -- | Intuitively, the operation of pointing picks out a -- distinguished element from an underlying set. It is equivalent -- to the operator @x d/dx@: @'pointed' s = 'singleton' * 'differentiate' s@. pointed :: Species s => s -> s pointed = (x *) . Differential.differentiate -- $derived -- Some species that can be defined in terms of the primitive species -- operations. linOrds :: Species s => s linOrds = linOrd elements :: Species s => s elements = element -- | An octopus is a cyclic arrangement of lists, so called because -- the lists look like \"tentacles\" attached to the cyclic -- \"body\": @'octopus' = 'cycle' ``o`` 'nonEmpty' 'linOrds'@. octopi, octopus :: Species s => s octopus = cycle `o` nonEmpty linOrds octopi = octopus -- | The species of set partitions is just the composition @'set' -- ``o`` 'nonEmpty' 'sets'@. partitions, partition :: Species s => s partition = set `o` nonEmpty sets partitions = partition -- | A permutation is a set of disjoint cycles: @'permutation' = 'set' -- ``o`` 'cycles'@. permutations, permutation :: Species s => s permutation = set `o` cycles permutations = permutation subsets :: Species s => s subsets = subset -- | The species of ballots consists of linear orderings of -- nonempty sets: @'ballot' = 'linOrd' ``o`` 'nonEmpty' 'sets'@. ballots, ballot :: Species s => s ballot = linOrd `o` nonEmpty sets ballots = ballot ksubsets :: Species s => Integer -> s ksubsets = ksubset -- | Simple graphs (undirected, without loops). A simple graph is a -- subset of the set of all size-two subsets of the vertices: -- @'simpleGraph' = 'subset' '@@' ('ksubset' 2)@. simpleGraphs, simpleGraph :: Species s => s simpleGraph = subset @@ (ksubset 2) simpleGraphs = simpleGraph -- | A directed graph (with loops) is a subset of all pairs drawn -- (with replacement) from the set of vertices: @'subset' '@@' -- ('element' '><' 'element')@. It can also be thought of as the -- species of binary relations. directedGraphs, directedGraph :: Species s => s directedGraph = subset @@ (element >< element) directedGraphs = directedGraph