Parameter Utilities

by Dave Herman (dherman at ccs dot neu dot edu)

This library provides several utilities for parameters.

1 Getting Started

Everything in this library is exported by a single module:

(require (planet dherman/parameter:1))

2 Pseudo-Parameters

A pseudo-parameter is like a PLT Scheme parameter, but comprises both an accessor and a mutator function. This can be used, for example, to create compound parameters that simultaneously update multiple parameters.

(make-pseudo-parameter getter setter) → (pseudo-parameter/c a)

getter : (-> a)

setter : (a -> any)

Constructs a new pseudo-parameter with getter and setter functions.

(pseudo-parameter? x) → boolean?

x : any

Determines whether a given value is a pseudo-parameter.

(pseudo-parameter/c c) → contract?

c : contract?

A contract constructor for pseudo-parameters with an underlying value of contract c.

3 Parameter Sets

A parameter set is a collection of PLT Scheme parameters that can be read or written to all at once with a prefab structure. Because the structure is prefab, a parameter set can also easily be marshalled and demarshalled (assuming its values are all writeable, of course).

(define-parameter-set struct-id pseudo-id   (param-id default-expr maybe-guard) ...)

maybe-guard   =       |   guard-expr

Defines a parameter set. The struct-id is defined as a prefab structure type with one field for each parameter in the set, in declaration order. The pseudo-id is defined as a pseudo-parameter that reads or writes the values of all the parameters in the set simultaneously. Each param-id is defined as a parameter with default value computed by default-expr and optional guard computed by maybe-guard.