In my favourite homoiconic language, Racket (also in lisps, so it's surprising that OP didn't mention it) you'd typically accomplish it with parameterised dynam

In my favourite homoiconic language, Racket (also in lisps, so it's surprising that OP didn't mention it) you'd typically accomplish it with parameterised dynamic binding. Think global variables, except the lifetime of the new value is limited to a body of code. A concrete example is a function that writes something to stdout. If you want to output to a file instead, parameterise the function call by setting current-output-port to the handle of your file.