Some utility functions around gregor🔗ℹ

1 Utility functions🔗ℹ

procedure
(date->moment dt) → moment?
dt : (or/c date? date*?)

Converts a racket "date" or "date*" structure to a gregor "moment". When it converts, it will assumes two kinds of dates.

The first being a standard racket date structure with a time zone offset.
The second for a date* structure, that will hold a named local timezone or ’UTC’.

This function will check if the date* structure is UTC time or local timezone. If it is local timezone, it will use the function "(system-tzid)" of tzinfo to determine the local timezone id, that can be used to create a new gregor "moment".

As date* will be either localtime or UTC, we’re working with what we got. We can recognize UTC, but the timezone name will be something OS specific, e.g. on a dutch windows system: "West-Europa (zomertijd)". This is reported e.g. in the windows powershell command:

> get-timezone:

  Id                         : W. Europe Standard Time
  DisplayName                : (UTC+01:00) Amsterdam,Berlijn,Bern,Rome,Stockholm,Wenen
  StandardName               : West-Europa (standaardtijd)
  DaylightName               : West-Europa (zomertijd)
  BaseUtcOffset              : 01:00:00
  SupportsDaylightSavingTime : True

But, as the racket standard date functions only work with UTC and localtime, we can request the current timezone tzinfo’s "(system-tzid)" for localtime and use UTC for univeral time.

procedure
(moment->date m) → date*?
m : moment?

Converts a gregor "moment" to a standard racket "date*".

procedure
(racket-date? d) → boolean?
d : any/c?

Returns #t, if d is of racket’s standard type "date" or racket{date*}.