Re: RFC: String interpolation

[Paul Eggert]

Why not just extend "format" so that it allows trailing "...%" in the 
format string to mean "argument value spliced here"? After the argument 
you can continue on with the format, which must start with the rest of 
the conversion specification. E.g.:

  (format "Altitude= %" alt ".2f, direction = %" dir ".2f.")

might output "Altitude = 300.57, direction = 240.93."

That way, you can easily replace the expressions without giving them names:

  (format "Altitude= %" (+ alt 100) ".2f, direction = %" (- dir) ".2f.")

This should provide the desired benefits without having to do anything 
fancy with variable scoping or changing the lexer or whatever.