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exiting let block early due to errors opening files

MOSFET

The documentation for let and prog says that let is generally preferred for performance reasons but prog allows you to break out of the prog block early using a return() call, whereas let does not have this functionality.  My question is: if I want to use let for performance reasons, how would I break out of the entire procedure if I encounter an error due to a file that can't be opened, copied, written, etc.?  For example, suppose I have the following:

procedure(foo(libName cellName)

    prog(()

        cv = dbOpenCellViewByType(libName cellName "layout" "maskLayout" "r" )

        if((scv == nil) then

            printf("ERROR: Unable to open lib %L, cell %L, view layout, viewType maskLayout for read, exiting...\n" libName cellName)

            return()

        )

    )

)

Suppose I used let instead of prog in the example above and dbOpenCellViewByType returned nil.  How would I break out of the procedure foo given that return() is not available in a let() block?

  • Andrew Beckett

    I talk a bit about this in my Writing Good SKILL Code (Video). I have a bit of an aversion to using prog, which dates from it having worse performance than let, but nowadays that difference is very small and probably not worth worrying about. My main issue is that it's effectively a glorified goto and is "spaghetti programming" - hard to follow the flow (this is probably a philosophical thing that was drummed into me by a high school computer science teacher!).

    Anyway, you could use make the code conditional, or you could use the catch/throw mechanism - but probably it's simplest just to continue using prog and return.

    Andrew.

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