@let()

The @let() function takes a series of functions, in pairs of a %substitution
name and a value for it, and a final code argument.  The function executes
the code with the %subs set to the values given.

Usage (recall that => is equivalent to comma):
@let( "number" => @getfield( #1234, "num" ), "%{number} bottles of beer on the wall,
  %{number} bottles of beer" )