Description:

interpolation with quasi-quotation: stick haskell variables into haskell
strings

Note there is no dependency on haskell-src-extras. If you don't mind that
dependency, you may want to look at using these packages: Interpolation,
interpolatedstring-perl6, interpolatedstring-qq.

This package has 1 other general feature that those others may not (but would
be easy to duplicate): instead of using quasi-quoting you can also use an
external file. It also has url/embeding interpolation, with \@ and \^, which
are used in Yesod.

This package also uses blaze-builder for efficiently constructing strings (I am
not sure what the other packages use). This might be of interest to you for
large templates or performance sensitive code, or otherwise having a nice
interface to blaze-builder

Shakespeare is a template family for type-safe, efficient templates with simple
variable interpolation . Shakespeare templates can be used inline with a
quasi-quoter or in an external file. Shakespeare interpolates variables
according to the type being inserted. In this case, the variable type needs a
ToText instance.

Please see http://www.yesodweb.com/book/shakespearean-templates for a more
thorough description and examples of the shakespeare family of template
languages.