Templates can be created in code using the lit and placeholder functions with the Monoid instance, or by parsing a template string:

import Data.Monoid ((<>))

t1 = placeholder "lastName" <> lit ", " <> placeholder "firstName"
t2 = parseTemplate "{{lastName}}, {{firstName}}"

Templates can be applied using the applyTemplate function:

>>> :set -XOverloadedStrings
>>> let vals = [("firstName", "Haskell"), ("lastName", "Curry")]
>>> applyTemplate (`lookup` vals) t1
Just "Curry, Haskell"