Time in PureScript

module Main where

import Prelude

import Effect (Effect)
import Effect.Console (log)
import Data.DateTime (DateTime, Year(..), Month(..), Day(..), Hour(..), Minute(..), Second(..), Millisecond(..), adjust)
import Data.DateTime.Instant (Instant, unInstant, toDateTime)
import Data.Time.Duration (Milliseconds(..), Days(..), negateDuration)
import Data.Enum (toEnum)
import Data.Maybe (fromMaybe)
import Effect.Now (now)

main :: Effect Unit
main = do
  -- We'll start by getting the current time.
  nowInstant <- now
  log $ show $ toDateTime nowInstant

  -- You can build a DateTime by providing the year, month, day, etc.
  let then' = fromMaybe bottom $ 
        DateTime <$> toEnum 2009 
                 <*> pure November 
                 <*> toEnum 17 
                 <*> toEnum 20 
                 <*> toEnum 34 
                 <*> toEnum 58 
                 <*> toEnum 651
  log $ show then'

  -- You can extract the various components of the DateTime value as expected.
  log $ show $ (\(Year y) -> y) $ year then'
  log $ show $ month then'
  log $ show $ (\(Day d) -> d) $ day then'
  log $ show $ (\(Hour h) -> h) $ hour then'
  log $ show $ (\(Minute m) -> m) $ minute then'
  log $ show $ (\(Second s) -> s) $ second then'
  log $ show $ (\(Millisecond ms) -> ms) $ millisecond then'

  -- The day of the week is also available.
  log $ show $ weekday then'

  -- These functions compare two DateTimes, testing if the
  -- first occurs before, after, or at the same time
  -- as the second, respectively.
  log $ show $ then' < toDateTime nowInstant
  log $ show $ then' > toDateTime nowInstant
  log $ show $ then' == toDateTime nowInstant

  -- We can compute the duration between two DateTimes.
  let diff = unInstant nowInstant - unInstant (fromMaybe bottom $ toInstant then')
  log $ show diff

  -- We can compute the length of the duration in various units.
  log $ show $ diff / 3600000.0 -- hours
  log $ show $ diff / 60000.0 -- minutes
  log $ show $ diff / 1000.0 -- seconds
  log $ show diff -- milliseconds

  -- You can use `adjust` to advance a DateTime by a given
  -- duration, or with a negative duration to move backwards.
  log $ show $ adjust (Milliseconds diff) then'
  log $ show $ adjust (Milliseconds (-diff)) then'

This PureScript code demonstrates working with dates and times. Here’s a breakdown of the translation:

We use the Data.DateTime and related modules for date and time operations.
The time.Now() function is replaced with Effect.Now.now.
Creating a specific date and time is done using the DateTime constructor with toEnum for each component.
Extracting components from a DateTime is done using functions like year, month, day, etc.
Comparisons between DateTime values are done using standard comparison operators.
Duration calculations are performed using milliseconds.
The Add method is replaced with the adjust function.

Note that PureScript’s type system and functional nature lead to some differences in how we handle potential errors (using Maybe) and how we extract values from newtypes (using pattern matching).

To run this program, you would typically compile it with the PureScript compiler and then run it with Node.js, assuming you have the necessary dependencies installed.

$ pulp run

This will compile the PureScript code and run the resulting JavaScript.

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