Functions

A major feature of the Ly language is its functions, which we will go over now.

Defining a function

Defining a function is simple:

<name>{<code>}

where <name> is a single character denoting the name of your function, and <code> is the body of your function.

Inside a function, code is executed just like a completely seperate Ly program. The only connection between a function and the main program is the input and output commands.

Instead of performing I/O from STDIN and STDOUT, a function takes input from parameters passed to it when it is called, and output is pushed to the stack of the main program.

An example function looks like this:

p{ns::[1-s%![l%!u;]p:l]}

This is a simple prime number checker program wrapped up in a function named p that takes a single number as a parameter and pushes either 0 or 1 to the stack depending on if the number passed was a prime or not.

Calling functions

Calling functions is just as simple as creating them. In fact, the syntax is the same!

<name>{<parameters>}

where <name> again is the name of the function and <parameters> are the parameters you want to pass to it.

The syntax for parameters is comma-seperated numbers that will be passed to the function. There are also two special values you can pass: c and i.

The interpreter parses your parameters into a single string of input that will be parsed to the function, like so:

• c will be replaced by a value popped from the stack and turned into a character.

• i will be replaced by a value popped from the stack.

• A number will be added directly to the string with a space at the end.

Then, the function is run like it is a normal program with the parsed string as input. Any time the function tries to print a value, it will be added to the stack of the main program instead.

Here is an example call of the prime number function:

p{i}

This will pop a number from the stack, and push 1 if it was prime and 0 otherwise.