[feature request] User-defined booleans (and special values)

[Poshi]

Dear @johnkerl,

the booleans in Miller are clearly defined as

boolean: literals true and false; results of ==, <, >, etc.

The result of comparisons are internal and will always be booleans, but for the external boolean data it can only be "true" or "false" to be considered as a boolean. The world is vast and many other languages (or businesses) have other representation. For example, I work quite a lot with Python, and printing a boolean yields "True", not "true":

$ python -c "print(1==1)"
True

Some other system or business could decide to use "on/off", or "up/down", or "TRUE/FALSE"... Covering all the possibilities by default is impossible, but being able to configure which strings should be considered as truth values would be a nice addition, so someone working with a system that usually uses "True/False" should be able to do that natively without conversions or having to compare strings. Beware that some formats have these values fixed: in JSON files, you can only use bare "true/false" (no quotes) to represent the booleans. My comment only serves for the formats where the boolean values are not well defined like CSV.

I'm aware about No autoconvert to boolean, but I think that this is not related to the issue: I'm just asking to have user-configurable boolean literals, as we already have a couple of literals for that duty.

Thanks for your effort!