Examples of using Functor in English and their translations into Chinese
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Programming
In Haskell, for a type to be a monad it has to be also a functor and applicative.
In this new sideways interpretation of Cat there are two ways of getting from object to object: using a functor or using a natural transformation.
A monad is a functor M: C→ C{\displaystyle M: C\to C}, along with two morphisms[2] for every object X in C.
These maps are"natural" in the following sense: the double dual operation is a functor, and the maps are the components of a natural transformation from the identity functor to the double dual functor. .
More abstractly,"G-bundles over X" is a functor in G: given a map H→ G, one gets a map from H-bundles to G-bundles by inducing(as above).
A simplicial object is a presheaf on Δ{\displaystyle\Delta}, that is a contravariant functor from Δ{\displaystyle\Delta} to another category.
A functor is essentially a transformation between categories, so given categories C and D, a functor F: C→ D{\displaystyle F: C\to D}.
If F and G are contravariant functors one speaks of a duality of categories instead.
Suppose we have two functors and.
F is a left adjoint of G and both functors are full and faithful.
We have two functors.
G is a right adjoint of F and both functors are full and faithful.
F is a left adjoint of G and both functors are full and faithful.
Instances of those classes are called functors or function objects.
Java made you use functors, which is even uglier.
Functors often describe"natural constructions" and natural transformations then describe"natural homomorphisms" between two such constructions.
These isomorphisms are"natural" in the sense that they define a natural transformation between the two involved functors Abop x Abop x Ab-> Ab.
Categories, functors and natural transformations were introduced by Samuel Eilenberg and Saunders MacLane in 1945.
Since all standard algebraic data types are functors, any polymorphic function between such types is a natural transformation.
Then Alexander Grothendieck used derived functors of the global section functor, providing a more definitive solution.