I am looking for a way to change the base phase of a namespace.
Or perhaps to make a new namespace with the same mappings except a
shift in phases.
I hope I have missed a trick, but I couldn't find a
namespace-shift-phase in the docs.
Consider the following program which defines a variable x to 0, 1, 2, and, 3
in phases 0, 1, 2, and, 3 respectively. It does so by evalunting the
forms in forms.
Then it displays the values of x in phases 1 and 2 with the results 1 and 2.
It does so by evaluating the forms in forms2.
I'd like to shift the base phase of the namespace (or make a copy with
new base phase),
so evaluating the forms in forms2 again will give results 2 and 3.
#lang racket
(define (eval* forms [ns (current-namespace)])
(for ([form forms])
(displayln (~a "> " form))
(eval form ns)))
(define forms '((module m0 racket (provide x) (define x 0))
(module m1 racket (provide x) (define x 1))
(module m2 racket (provide x) (define x 2))
(module m3 racket (provide x) (define x 3))
(require (for-meta 0 'm0))
(require (for-meta 1 'm1))
(require (for-meta 2 'm2))
(require (for-meta 3 'm3))))
(define forms2 '(; display the value of x in phase 1
(define-syntaxes () (begin (displayln x) (values)))
; display the value of x in phase 2
(define-syntaxes () (begin (let-syntaxes ([() (begin
(displayln x) (values))])
(void)) (values)))))
(define ns (make-base-empty-namespace))
(parameterize ([current-namespace ns])
; setup the namespace
(namespace-require '(for-meta 0 racket/base))
(namespace-require '(for-meta 1 racket/base))
(namespace-require '(for-meta 2 racket/base))
(namespace-require '(for-meta 3 racket/base))
; declare and require the modules
(eval* forms)
; display the value of x in phase 1 and 2
(eval* forms2) ; displays 1 and 2
; (namespace-shift-phase ns +1) ; on the wish list
; (eval* forms2) ; would display 2 and 3
)
The output is:
> (module m0 racket (provide x) (define x 0))
> (module m1 racket (provide x) (define x 1))
> (module m2 racket (provide x) (define x 2))
> (module m3 racket (provide x) (define x 3))
> (require (for-meta 0 (quote m0)))
> (require (for-meta 1 (quote m1)))
> (require (for-meta 2 (quote m2)))
> (require (for-meta 3 (quote m3)))
> (define-syntaxes () (begin (displayln x) (values)))
1
> (define-syntaxes () (begin (let-syntaxes ((() (begin (displayln x)
> (values)))) (void)) (values)))
2
--
Jens Axel Søgaard
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