force, forceq, forceqq

Arguments

Returns

The s_exp argument.

Description

These functions are idential to the set, setq, and setqq, functions, except in addition to assigning a value to a symbol, and being the functional equivalent of the = (assignment) operator, these functions force Gamma to evaluate the change functions for the symbol even if the value has not changed.

This function is particularly useful when working with DataHub points that contain arrays. Gamma handles arrays from the DataHub by mapping them automatically into Gamma arrays, so you can address individual elements. However, in Gamma, if you have a DataHub array point, represented as $default:myarray, you can modify an element of the array normally, such as $default:myarray[0] = 17; but that does not automatically write back to the DataHub, so nothing gets updated. You have to rewrite the point. Logically you would do this: $default:myarray = $default:myarray; to reassign the point. But this is a null operation since you are just assigning the same value again to the point. Using force, forceq, forceqq like this: force(#$default:myarray, $default:myarray); forces the point change to be sent back to the DataHub.

The force function evaluates both of its arguments, forceq evaluates only its second argument, and forceqq evaluates neither of its arguments. A symbol's value is the value returned as a result of evaluating that symbol. Symbols constitute the Lisp mechanism for representing variables. These functions can only affect the value of a symbol in the current scope.

See Also

Assignment Operators, set, setq, setqq