A small guide on writing interpreters, part 2

label hello: select dialog("Hello! What would you like to do?") {
    option "Count to 5":
        for (var i = 1; i <= 5; i = i + 1) {
            trace(i + "!");
        return 1;
    option "Nothing": jump yousure;
label yousure: select dialog("You sure?") {
    option "Yes": trace("Well then,"); return 0;
    option "No": jump hello;

Example of supported syntax

As some might remember, earlier this year I have published a small guide on writing interpreters, which went over the process of implementing a basic interpreter capable of evaluating expressions consisting of numbers, operators, and variables.

This continuation of the guide further expands upon concept, outlining how to support calls, statements, and branching - enough for a small scripting language.

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GameMaker: Checking whether a string is a valid number

Some things are numbers, some aren't

GameMaker Studio 2.2.2 released few days ago, bringing, among improvements, "GML consistency", which changes how automatic type conversion works in corner cases.

A little less known thing, together with that it also changed how GameMaker's string-to-number conversion function (real) works, having it throw an error if your string is definitely not a number.

A slight inconvenience, given that there is not a function to check if a string is a number before attempting conversion.

But, of course, that can be fixed.

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GameMaker: Simplest possible instance methods

A tutorial about implementing instance methods in GameMaker.

After seeing series of increasingly strange uses of "user events" in GameMaker games for object-bound actions, it came to my attention that most people are only vaguely aware of other ways of doing things, so I decided to write a small blog post on the matter.

There are many uses for these - for example, you might want to have a "take X damage" method on your enemy objects so that it can be varied depending on requirements - some enemies might just take damage, some should retaliate on being hit, some might have a fancy damage reduction formula. Being able to comfortably define/redefine methods on per-object-type basis can help a lot.

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Variable references in GameMaker

A tutorial about variable references in GameMaker.

Sometimes you might want to pass an instance variable by reference rather than by value - to have a script modify instance variable(s) passed to it without having to return them, or have an instance save a reference to variable(s) that it should change on other instance, or doing anything else that would usually imply using pointers.

But it might seem like GameMaker does not support such things... or does it? Well, we'll make it.

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