If the macro can ask for the value of the variabl

20. Named parameters and HAL items
To read arbitrary HAL pins, signals and parameters from G-code, use the following named parameter syntax:
#<_hal[hal_name]>
where hal_name may be a pin, parameter or signal name.
Example:
(debug, #<_hal[motion-controller.time]>)
Access of HAL items is read-only. Currently, only all-lowercase HAL names can be accessed this way.
EXISTS can be used to test for the presence of a given HAL item:
o100 if [EXISTS[#<_hal[motion-controller.time]>]]
(debug, [motion-controller.time] exists: #<_hal[motion-controller.time]>)
o100 else
(debug, [motion-controller.time] does not exist)
o100 endif
This feature was motivated by the desire for stronger coupling between user interface components like GladeVCP and PyVCP to act as paramter source for driving NGC file behaviour. The alternative - going through the M6x pins and wiring them - has a limited, non-mmemonic namespace and is unncessary cumbersome just as a UI/Interpreter communications mechanism.