I'm kinda stuck here, and I could really use some help:
I want to define a function, let's call it quarterValue, that accepts a Rule as an input and returns an appropriate expression as output.
A template expression (a type of sorts?) of what the input is expected to be, is given below:
StringExpression["Q", DigitCharacter] -> _?NumericQ and as far as the output is concerned, I was going to give three different quarterValue definitions in order to account for the different possible input configurations (presented here from the most specific to the least specific), namely
ClearAll[quarterValue]quarterValue::err = "Error: `1`->`2`: `3`";(* catch missing values *)quarterValue[(q:StringExpression["Q", DigitCharacter]) -> ""] := q -> Missing[](* regular input *)quarterValue[(q:StringExpression["Q", DigitCharacter]) -> (nmc_?NumericQ)] := q -> nmc(* account for irregular input etc *)(* emit a Message and return the input unevaluated *)quarterValue[e:((q:StringExpression["Q", DigitCharacter]) -> x_)] := ( Message[quarterValue::err, q, x, e]; e )I thought I was smart enough but the Kernel had other plans.
I was anticipating that
quarterValue[StringExpression["Q", DigitCharacter] -> (whatever_)] would match against input values, because StringMatchQ["Qi", StringExpression["Q", DigitCharacter]], where i is any value from {1,2,3,4}, matches every possible lhs of the input Rule and either "" or _?NumericQ or _ match the rhs of the input Rule.
It seems that, this is not the case.
How can I mix string and regular patterns in order to make the SetDelayed definition of quarterValue evaluate correctly?
