In the example below, I'm curious about the reason for the difference between
the behavior of the system parameter `error-print-width` and the custom
parameter `my-param`.
I understand why `my-param` doesn't take the parameterized value 'custom (=
because `namespace-require` causes a fresh instantiation of "param.rkt" in the
new namespace, which binds `my-param` with its default value).
But if that's the case, then why does `error-print-width` accept the
parameterized value? Why doesn't it get instantiated at its default value of
250 when the new namespace is made?
;; param.rkt
#lang racket
(provide my-param)
(define my-param (make-parameter 'default))
;; param-test.rkt
#lang racket
(require "param.rkt")
(parameterize ([current-namespace (make-base-namespace)]
[error-print-width 4242]
[my-param 'custom])
(namespace-require "param.rkt")
(namespace-require 'rackunit)
(eval '(begin (check-equal? (error-print-width) 4242) ;; not 250
(check-equal? (my-param) 'default))))
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