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Surely this function exists...

CADcasualty

I'm looking for a function that simply accepts a textual input and if the text can be numerically evaluated then return the evaluation, otherwise just return the string. Darned if I can find a function for this!

I've see evalstring() but it errors out too easily i.e. 

evalstring("1")
1
>
evalstring("fred")
*Error* eval: unbound variable - fred  <------------ yuck
>
evalstring("1+1")
2

Then I tried cdfParseFloatString():

cdfParseFloatString("1")

1.0
>
cdfParseFloatString("fred")
"fred"
>
cdfParseFloatString("1+1")
nil   <--------------yuck

So I wrote my own procedure:

procedure( myParse(myvar) if(errsetstring(myvar) evalstring(myvar) myvar) )

myParse("1")
1
>
myParse("fred")
"fred"
>
myParse("1+1")
2
>
myParse("1+fred")
"1+fred"


myParse does what I want without issue, but I'm loathed to use it because I just can't believe something like this doesn't already exist in skill. Can somebody please point me to the right function (again, assuming it exists).

  • Andrew Beckett

    There's nothing that quite does that. Not sure why you think there should be - the requirement to return the original string if you can't evaluate it is not something that universally useful.

    I can simplify your function using:

    procedure(myParse(var) car(errsetstring(var))||var)

    Regards,

    Andrew.

  • CADcasualty
    in reply to Andrew Beckett

    Thanks Andrew. I guess we have different opinions about how universally useful this function might be :-). Anyway, thanks for your simplified code. It took me a minute to understand why it wouldn't break if errsetstring was successful - if it returns something other than nil then there is no reason to continue with the OR function evaluation. I like the way you think! However in this case it crossed my line of readability vs functionally. Hopefully the entropy of the universe won't be overly impacted if I stick with my original code instead of yours :-).

  • Andrew Beckett
    in reply to CADcasualty

    Yes, this is a short-circuiting or operation - it only evaluates the second part if the first part is nil. The benefit is that it doesn't evaluate the expression twice - that might be a problem if the expression has side effects - for example:

    a=10
    var="a=a+5"
    myParse(var)

    In my case, it would return 15, whereas in your case it would return 20 because it got evaluated twice. 

    However, in normal situations you'd not have such a problem.

    Regards,

    Andrew.

  • CADcasualty
    in reply to Andrew Beckett

    Thanks for going the extra mile with this response. I always learn something new every time you post!

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