Alt() works differently in script and in front end

[jonathandienst]

Consider the following script fragment:

Set x1 = 1;
Let x2 = 2;

Let z1 = Alt(x1, 100);
Let z2 = Alt(x2, 200);

Let e1 = IsNum(x1);
Let e2 = IsNum(x2);

This produces the following results:

Notice that the Alt(x1, 100) considered x1 to be non-numeric, whereas IsNum(x1) sees x1 as numeric. Furthermore, in the front end, we get this:

So x1 is being seen as numeric by Alt() and IsNum() in the front end expressions, and in the script it is considered numeric by IsNum(), but non-numeric by Alt().

In the case where this behaviour was observed, the Set x1  = 1 expression is dynamically generated from a configuration file. The Alt() was required to provide a default if the configuration file did not have a definition of x1.

The workaround is to change the config loader to generate the values with Let, but if that is not an option, use an expansion:

Let z1 = Alt($(x1), 100);

Version 11.2 SR15 11.20.13405.0

[marcus_sommer]

I'm not sure if this behaviour is really unexpected then Set x1 = 1; assigned a string to the variable and Let x2 = 2; creates an dual-value with 2 as string and 2 as numeric value. Therefore differ the alt-results by the z-variables. And I think isnum() instead will be evaluate it's input-value and at first check if the value is an (valid) dual-value and if it's not then it will check if the string-representation could be evaluated as number - and in this case both checks on the e-variables will be true.

Further I think the front-end treated the x1 variable as number because it sees it just as 1 and not as '1'.

- Marcus

[jonathandienst]

Marcus

That's my interpretation of the behaviour too (and that's why Let x = 1 does not have the problem) - it just seems inconsistent to me and it caused a hard to track down bug. IMO Alt() should act like IsNum() does and be the same in the script and in the front end.

[marcus_sommer]

Maybe hic could give some backgrounds if it's behaved expectedly or not and why there are differences between alt() and isnum().

- Marcus