Must

A must-declaration can be used to ensure that particular code is guaranteed to run before a block is finished, even if an error occurs or ret, exit, while, until or next is used to exit the block early.

Note

Since susp-expressions can resume the current block, they do not run must code. In general, do not use must-declarations with susp-expressions unless it known that the generating function will always be completed.

Note

In order to guarantee a valid state when each must-expression is executed, each must-declaration implicitly creates a new block around the code that follows it. Given code like:

decls
code
must X
decls
code

the compiler treats it internally as similar to:

decls
code
do
   decls
   code
   X
on Error do
   X
   Error:raise
end

This means that some forward declarations that work without must may not work when must is present. This limitation might be removed in the future.