The TpsParserFunction component works perfectly if all input variables are writable.
When you mix “read only” and “writable” variables, calculation is not fired anymore when the writable variables change but only when read only ones change.

To reproduce the issue you can drop on a form a TpsParserFunction and three TpsBool.
Set the first TpsBool variable as “Readonly”.
Drop two TpsCheckbox on the form and connect them to the first two TpsBool components.
Drop a TpsLabel and connect it to the third TpsBool.
Drop on the form also a button to toggle the value of the read only TpsBool (using the SetPropValue method).

Double click on the TpsParserFunction and add the first two TpsBool variables as inputs for the component.
Set the output property variable of the component to the third TpsBool (the result of calculation).
Set the Expression property of the component as ‘a*b’ (this is an ‘AND’ combination between input variables).

Run the application.
Toggle the value if the read only variable by pressing the button.
Check the second check-box and the result of the function will remain “False” (it should turn to “True”).
When you change the value of the read only TpsBool (pressing the button repeatedly) the result changes according to the espression we have set.
If you just toggle the check-boxe linked to the writable TpsBool nothing happens.