Calculator

bc -l is a useful minimal coprocess because it accepts line-oriented input and prints line-oriented output.

co-proc start calc bc -l

co-proc send calc '2 ^ 16'
co-proc read -t 1 calc

co-proc send calc 'scale=4; 22 / 7'
co-proc read -t 1 calc

co-proc stop calc

The repository includes a runnable version:

examples/calculator.zsh