$try / $catch / $endTry — Error Handling

The $try family of tokens provides structured error handling in BDFD scripts. Instead of letting a runtime error crash the entire action sequence, you can wrap risky code in a $try block and handle failures gracefully inside $catch. These are structural tokens processed at the parser level.

Block Structure

$try
 .. risky commands...
$catch
 .. recovery commands...
$endTry

1. The parser executes the body between $try and $catch.
2. If no error occurs, the $catch block is skipped entirely and execution resumes after $endTry.
3. If any error occurs inside the $try body, execution immediately jumps to $catch. The error is consumed — it will not propagate outside the try-catch.

Important: $endTry is always required, even if no $catch is provided.

The $error Variable

Inside the $catch block, the $error variable provides access to the caught error’s metadata:

Usage	Returns
$error	The error message as a string
$error[message]	Same as above — the error message
$error[command]	The name of the command that caused the error
$error[source]	The source line or context of the error
$error[row]	The row number where the error occurred
$error[column]	The column number where the error occurred

Outside the $catch block, $error is empty or undefined. It only has meaning within the catch scope.

Nesting

$try blocks can be nested. Each $catch only catches errors from its own $try body. An error caught in an inner $catch does not propagate to an outer $catch.

Interaction with $stop

If $stop is called inside a $try block, it halts execution before the $catch is reached — so the error handler does not run. This is by design: $stop is an unconditional halt.

Use Cases

• API calls: Wrap $httpGet / $httpPost calls to handle network failures.
• User input parsing: Catch errors when parsing or coercing user-supplied values.
• Fallback logic: Try a primary operation, fall back to a secondary on failure.
• Logging: Use $catch to log errors with $eprint or save them to a variable for later inspection.

Common Pitfalls

• Forgetting $endTry produces a parse error.
• Placing $endTry before $catch — the parser expects $catch before $endTry.
• Assuming $error is available outside $catch — it is scoped to the catch block only.
• Catching an error but doing nothing with it — at minimum, log it to help with debugging.