The 5 categories of bugs

Syntax errors

Your parser won’t make it past this no matter what language.¹ You get immediate feedback if you haven’t stated something correctly.

Linking, reference & type errors

Where your code references other code incorrectly. A compiled language, with a linker, won’t compile on this. Javascript, and most dynamic languages, will run just fine and only crash when it tries to execute that instruction. This is a slow feedback loop, especially if its in error handling code that is hard to test. Building, refreshing your browser, navigating to that page, opening the drawer, creating a new resource, saving… finally to see that you misspelled savve(). Other ways to cause these errors is to pass arguments in the wrong order, pass the wrong number of arguments, use or compare the wrong types, etc.

Forgetting to handle a failure scenario

This is any time your code crashes because of an exception. Most languages have a way to catch exceptions, if you remember, so you can handle them gracefully without crashing. Some languages are a mixture of value errors and exceptions (Elixir). A current trend is toward value errors even though languages that only support value errors have been around for decades (ML). Interestingly, if you introduce just 2 more ideas, Algebraic Data Types and Exhaustive Matching, you can define a language where runtime errors don’t happen in practice. (Elm, Rust)

Executing the wrong code at the wrong time

Calling the wrong function, infinite loops, forgetting a condition, unsanitized user input. Declarative languages help a lot with this, but I don’t know of anything that can reliably detect or prevent it. I mean, proving logically if a function ever stops executing is a known intractable problem. Some causes of this are: calling the wrong function, not understand the code, forgetting possible states. Both security and performance bugs fall under this category. A thoughtfully used language with advanced types² can help mitigate this, but all languages will compile and run with these types of errors. These are the hardest types of errors to catch and thorough tests are the only way I know how to drastically reduce them.

“Works as designed” but the designs are wrong

You, as the programmer, are blameless. Product told you to do something stupid that all users consider the totally wrong behavior. This is a bug, but it’s not yours. Some examples of this are: telling people they unsubscribed from your newsletter when they really didn’t. Or a website that can’t load fast because there are too many 3rd party ads and trackers.

Humans make mistakes, but we tighten our feedback loops and make less mistakes with languagues that prevent entire categories of errors.