Error Messages

Why Do Errors Matter?

Imagine you're doing a maths test and your teacher marks one answer wrong -- but doesn't tell you which question, which part, or what went wrong. Frustrating, right?

A good compiler is like a helpful teacher. When something goes wrong, it doesn't just say "Error!" -- it circles the exact mistake on your homework, underlines the word, and explains what it expected instead.

The Pebble Error System

Pebble has a family of error types, one for each stage of the compiler:

Error Type	When It Happens	Example
LexerError	Scanning characters	Unterminated string "hello
ParseError	Arranging tokens into a tree	Missing closing )
SemanticError	Checking the tree for logic mistakes	Using a variable that doesn't exist
PebbleRuntimeError	Running the bytecode	Dividing by zero
PebbleImportError	Loading a module	File not found, circular import

All of them are part of the same family (they inherit from PebbleError), so the compiler can catch any Pebble error when it needs to.

Anatomy of an Error

Every Pebble error carries three pieces of information:

1. Message -- What went wrong, in plain English
2. Line -- Which line of your code has the problem
3. Column -- Which column (character position) on that line

The Caret Pointer

When Pebble reports an error, it shows you the broken line from your source code and draws a little arrow (^) pointing to the exact spot:

1 | let x = @
        ^
Unexpected character '@'

This is like a teacher using a red pen to circle the mistake. You don't have to hunt through your whole program -- the compiler shows you right where to look.

Here's one from line 3 of a longer program:

3 | print(x + )
               ^
Expected expression after '+'

Collecting Multiple Errors

Some compilers stop at the first error they find. That's like a teacher who reads one sentence of your essay, finds a spelling mistake, and hands it straight back without reading the rest.

Pebble's ErrorCollector is smarter. It gathers up all the errors it can find and reports them all at once. That way, you can fix several mistakes in one go instead of playing whack-a-mole -- fix one, run again, find the next, fix it, run again...

1 | let x = @
            ^
Unexpected character '@'

3 | print(y
            ^
Expected ')' after argument

Two errors, reported together. Much more efficient!

Summary

Concept	Analogy
Error message	A teacher circling mistakes on your homework
Line & column	"Page 3, second paragraph, fifth word"
Caret pointer	A red arrow drawn under the mistake
ErrorCollector	Marking all mistakes at once, not just the first