Yet Another Useless Language Part 8 — Function

This is the eighth part of the YAUL series. For your convenience you can find other parts in the table of contents in Part 1 — Introduction

Today we are going to handle functions in YAUL. Let’s go.


We are going to represent functions as blocks of code. Since we want to handle local variables, we will need to add them to scope and remove after creating the function. We also need to handle names duplicates and conflicts with functions defined in standard library. The code will be little longer today.


Let’s begin with PLY:

It looks very similar to code for loops. One additional thing is list of parameters:

However, there is a very special keyword for functions: return. We can return value or just exit the function:

What’s more, we would like to be able to call our functions:

This is it, nothing tricky here.


We start with function definition:

Let’s examin Accept function. First, we create expressions for parameters. Next, we add them to local scope so they can be used as local variables. Next, we visit body. Since we have local variables in scope, body is free to use them. When it is done, we remove parameters from scope. Next, we create block for function, create expression holding our function, clear local parameters, and we are done.

PreparedFunction looks as follows:

Function’s parameters are defined as:

And return instruction:

Please note, that we always return something, but in case when we want to exit the function, we simply ignore the value.

Anod now the last part, calling functions:


Function handling is the most difficult part in our language, however, there is no magic. Wee simply need to write a little more code to correctly handle and create function’s block. Next time we are going to handle standard library.