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3. Error Handling

Error Handling

Like normal Luau, Eryx raises errors with error() and traps them with pcall(). There is one important difference you'll run into almost immediately, so it's worth covering up front.

Errors are Exceptions

In normal Luau, whatever value you pass to error() is exactly what pcall() hands back:

-- Normal Luau
local ok, err = pcall(function()
    error("something went wrong")
end)
print(err) -- "main:2: something went wrong" (the raw string)

In Eryx, the value you pass to error() is not "the error" itself. Instead it becomes the message attached to a richer Exception object, and that Exception is what pcall() returns:

local ok, err = pcall(function()
    error("something went wrong")
end)

if not ok then
    print(err.message)    -- "something went wrong"
    print(err.type)       -- "thrown"
    print(err.traceback)  -- the captured traceback
end

So the key thing to remember: after a failed pcall, err is an Exception, not the string you threw. Reach for err.message to get the text back.

Printing a readable error

The exception library can format an Exception into a complete, human-readable report (message plus traceback):

local exception = require("@eryx/exception")

local ok, err = pcall(function()
    error("something went wrong")
end)

if not ok then
    print(exception.format(err))
end

Checking what went wrong

Because the error is a structured object, you can inspect it instead of pattern-matching on a string. Every Exception carries a type, and you can recognise one with typeof:

local ok, err = pcall(risky)
if not ok and typeof(err) == "Exception" then
    -- handle the failure using err.type, err.message, etc.
end

This is also the guard to use if you're writing code that needs to run on both Eryx and stock Luau, where err would be a bare value.

For the full picture (how tracebacks survive re-raising across pcall boundaries, exception causes such as the interrupt raised on Ctrl+C, and the design behind all of this) see Exceptions under Writing Code with Eryx, and the exception API reference.