post-execution on an interrupted SKILL routine

What you need here is unwindProtect(). Here's a little example showing the principle - if you call runIt() and then use control-C during the run (quite easy to do because there are a trillion inner loop points, so enough time to interrupt it!), you'll see that the UNIX env var gets returned to its initial value (which you can check with getShellEnvVar("SOMEVAR") of course).

procedure(verySlow()
  let((a)
    a=0
    for(i 1 1000000
      a=a+i
    )
    a
  )
)

procedure(extremelySlow()
  let((b)
    for(j 1 1000000
      b=mod(j 100)
      when(b==0
        printf("%d\n" j)
      )
      verySlow()
    )
  )
)

procedure(runIt()
  setShellEnvVar("SOMEVAR" "CHANGED")
  ; first function is form to be evaluated, and second is
  ; what to do as cleanup when the stack is unwound (because of
  ; error or interrupt). If you need more than one statement, 
  ; surround each with {} or a let() or something like that
  unwindProtect(
    extremelySlow()
    setShellEnvVar("SOMEVAR" "INITIAL")
  )
)

setShellEnvVar("SOMEVAR" "INITIAL")

Thank you so much Andrew!

Actually I do have more than one statement for the cleanupForm (the second function).

Can you provide a sample of what you mean by enclosing each with { } or a let()?

I'm not understanding the correct syntax of that part.

Sounds like I could put the cleanupForm into a separate procedure.

Also, it looks like the final setShellEnvVar() would need to be placed as the last line of the runIt() procedure, following the unwindProtect().

The unwindProtect functions works like this:

unwindProtect(
    expressionToEvaluate
    expressionToAlwaysRunAtEnd
)
expressionThatIsNotGuaranteedToBeRun

the second expression within the unwindProtect will always run, even if the first is interrupted, or fails with an error. The expression after the unwindProtect (that follows it) will not be evaluated if the code was interrupted or an error occurred, so you definitely do NOT what the final setShellEnvVar as the last line of the runIt procedure, following the unwindProtect().

If  you want more than one expression to evaluate, or more than one expression to always run at the end, you need to either put those into a function you call, or simply group them:

unwindProtect(
    {
        firstExprToEvaluate
        secondExprToEvaluate
        ...
        finalExprToEvaluate
    }
    {
        firstExprToAlwaysRunAtEnd
        ...
        finalExprToAlwaysRunAtEnd
    }
)
expressionThatIsNotGuaranteedToBeRun

Note that instead of using {} you could also use other grouping functions, such as let or prog:

unwindProtect(
    let((someLocalVar anotherLocalVar)
        firstExprToEvaluate
        secondExprToEvaluate
        ...
        finalExprToEvaluate
    )
    {
        firstExprToAlwaysRunAtEnd
        ...
        finalExprToAlwaysRunAtEnd
    }
)
expressionThatIsNotGuaranteedToBeRun

Hope that's clearer?

Regards,

Andrew.

The unwindProtect functions works like this:

unwindProtect(
    expressionToEvaluate
    expressionToAlwaysRunAtEnd
)
expressionThatIsNotGuaranteedToBeRun

the second expression within the unwindProtect will always run, even if the first is interrupted, or fails with an error. The expression after the unwindProtect (that follows it) will not be evaluated if the code was interrupted or an error occurred, so you definitely do NOT what the final setShellEnvVar as the last line of the runIt procedure, following the unwindProtect().

If  you want more than one expression to evaluate, or more than one expression to always run at the end, you need to either put those into a function you call, or simply group them:

unwindProtect(
    {
        firstExprToEvaluate
        secondExprToEvaluate
        ...
        finalExprToEvaluate
    }
    {
        firstExprToAlwaysRunAtEnd
        ...
        finalExprToAlwaysRunAtEnd
    }
)
expressionThatIsNotGuaranteedToBeRun

Note that instead of using {} you could also use other grouping functions, such as let or prog:

unwindProtect(
    let((someLocalVar anotherLocalVar)
        firstExprToEvaluate
        secondExprToEvaluate
        ...
        finalExprToEvaluate
    )
    {
        firstExprToAlwaysRunAtEnd
        ...
        finalExprToAlwaysRunAtEnd
    }
)
expressionThatIsNotGuaranteedToBeRun

Hope that's clearer?

Regards,

Andrew.

Hi Andrew,

Yes, that is much clearer - thank you so much again.  The description in the SKILL Language Reference is pretty spartan.

Based on my incorrect interpretation of how unwindProtect actually works, your initial example looked something like this :

procedure(verySlow()...); proc

procedure(extremelySlow()...); proc

procedure(runIt()...);proc

setShellEnvVar()

It didn't make sense to me that the final setShellEnvVar() was standalone.

I had thought that the second function of unwindProtect() only executed in the case of an interrupt, and so was needed to include following unwindProtect() in the case of no interrupt.

Sorry, I should have put a comment before that final top-level setShellEnvVar - it's there purely so that some initial value of the env var was set when I loaded the file.

I'll take a look at the documentation tomorrow, and probably file a request with tech pubs to improve it (it wouldn't surprise me if it isn't terribly expansive with its explanation...)

Regards,

Andrew.