`OS_SWINumberFromString` equivalent API call?

[stevesims]

BASIC V on RISC OS's SYS keyword allowed for direct calling of OS APIs. Simplistically it was a wrapper over the SWI mechanism, and conceptually therefore similar to Agon MOS's RST 8

Whilst you could use SWI numbers on RISC OS with the BASIC SYS keyword, it was more common to use a string, such as "Wimp_Poll". When used in this manner the BASIC interpreter would look up the SWI number via a call to OS_SWINumberFromString. This was a more user-friendly way to use SYS, making for much more readable/understandable code.

It'd be nice if the Agon BASIC V could support the string-based version of SYS, therefore we'd need an equivalent of OS_SWINumberFromString. It may also be nice to have OS_SWINumberToString as well.

Simplistically this is just a lookup table... If/when we implement MOS Modules #2 for modules that add in new API calls we'd likely want to allow those to include their own lookup tables

RISC OS documentation for this functionality can be found here:
https://www.riscosopen.org/wiki/documentation/show/OS_SWINumberFromString
https://www.riscosopen.org/wiki/documentation/show/OS_SWINumberToString
http://www.riscos.com/support/developers/bbcbasic/part3/keywords.html#sys

[stevesims]

Whilst arguably the nicest way to implement such an API on MOS would be to return back the API call number in the A register, allowing for simple calling on to the API after a lookup, doing this would be problematic. Firstly in MOS 2.1 onwards, unsupported APIs in MOS return a value of 23 in the A register, which would equate to a valid call to this API to look up "mos_ugetc". Secondly there's the issue of what to do for a lookup of an unknown string

we'll therefore probably wish to use A to return a standard status value, and a different register to return the API call number