Typist

Typist is a library for interpolation. It uses type-level strings (Symbols) for template. It uses UnconsSynbol type family which is added in GHC-9.2, so you need GHC version 9.2 or higher to use it.

Core functionality is in Typist.Internal.Format:

• Type family Format which transforms Symbol to function which renders final string
• Arg newtype over Text.Lazy.Builder which carries name of parameter and it's position in string on type-level (for perfomance goods)
• Type class Interpolate which renders final string on term level

An example of wrapping it (and also ready to use interface) is located in Typist.TextShow:

• Unquoted newtype for interpolation strings without \"
• #= set operator Example (more examples can be found in test/Test):

question = fmt @"Hello, #{name}, do you like #{dish}?" $ 
  (#name #= Unquoted "Mike") .
  (#dish #= Unquoted "pasta")

Performance is comparable with bare concatenation with <>. Benches can be found at test/Bench

O2

O1

O0

To run benchmark use

$ cabal bench --benchmark-options '--svg results_cpu.svg'