[procedure] make-parameter object [procedure]

SRFI-39, ChezScheme, Chicken, STklos, MzScheme, Gauche: creates a parameter with initial value object, and optionally, a filter procedure procedure.

Parameters are the procedure that takes zero or one argument; if no argument is given, it returns its current value; if one argument is given, the argument is set as the current value. Some implementations use pararmeters to keep global state.

In MzScheme, parameter values are thread-local.

See also parameterize, parameter?, parameter-procedure=??.

Guile has fluids, which is conceptually similar to parameters. See make-fluid.