String Interpolation 

String interpolations are written using INTERP(sym|"x", arg, ...):

INTERP(StringContext_s, LIT("Jello"), LIT(1), REF("x"))

INTERP("s", LIT("Hello"), LIT(1), REF("x"))

These examples print as:

s"Jello${1}$x"

s"Hello${1}$x"