Template Haskell

“Template Haskell” is the name of both Haskell’s entire metaprogramming infrastructure as well as a specific GHC extension that enables a number of language features that support it.

Most notably, enabling the TemplateHaskell extension allows you to write splices, that allow you to inject generated code into your code. Common uses of splicing include:

• Generating ToJSON and FromJSON instances

• Generating lenses

A related extension is QuasiQuotes, which provides a slightly different alternative to splicing.