Functions overview v17

Functions are standalone SPL programs that are invoked as expressions. When evaluated, a function returns a value that's substituted in the expression in which the function is embedded. Functions can optionally take values from the calling program in the form of input parameters.

In addition to the fact that the function returns a value, a function can also optionally return values to the caller in the form of output parameters. However, we don't encourage the use of output parameters in functions.