Time Formatting Parsing in PureScript

module Main where

import Prelude

import Effect (Effect)
import Effect.Console (log)
import Data.DateTime (DateTime, adjust)
import Data.Time.Duration (Minutes(..))
import Data.Maybe (fromMaybe)
import Data.Formatter.DateTime (formatDateTime, unformat)
import Data.Either (Either(..))

main :: Effect Unit
main = do
  now <- getCurrentDateTime

  -- Here's a basic example of formatting a time
  -- according to ISO8601, which is similar to RFC3339
  log $ formatDateTime "YYYY-MM-DDTHH:mm:ssZ" now

  -- Time parsing uses the same format strings as formatting
  case unformat "YYYY-MM-DDTHH:mm:ssZ" "2012-11-01T22:08:41+00:00" of
    Right parsed -> log $ show parsed
    Left err -> log $ show err

  -- Format using custom layouts
  log $ formatDateTime "h:mm A" now
  log $ formatDateTime "ddd MMM DD HH:mm:ss YYYY" now
  log $ formatDateTime "YYYY-MM-DDTHH:mm:ss.SSSZ" now

  -- Parse using a custom format
  case unformat "h mm A" "8 41 PM" of
    Right parsed -> log $ show parsed
    Left err -> log $ show err

  -- For purely numeric representations you can also
  -- use standard string formatting with the extracted
  -- components of the time value
  log $ formatDateTime "YYYY-MM-DDTHH:mm:ss-00:00" now

  -- Parsing will return an error on malformed input
  case unformat "ddd MMM DD HH:mm:ss YYYY" "8:41PM" of
    Right _ -> log "Parsed successfully"
    Left err -> log $ "Error: " <> show err

-- Helper function to get current date time
getCurrentDateTime :: Effect DateTime
getCurrentDateTime = do
  now <- now
  pure $ fromMaybe now $ adjust (Minutes 0.0) now

In PureScript, we use the purescript-formatters library for date and time formatting and parsing. This library provides similar functionality to Go’s time package, but with a slightly different API.

Here are some key differences and explanations:

PureScript uses Effect for side effects, similar to Go’s func main().
Instead of time.Now(), we use a helper function getCurrentDateTime that returns the current time.
The formatDateTime function is used for formatting dates, similar to Go’s Format method.
For parsing, we use the unformat function, which returns an Either type to handle potential errors.
PureScript doesn’t have built-in constants for date formats like RFC3339, so we use string patterns directly.
The date-time patterns in PureScript are slightly different from Go. For example, YYYY for year, MM for month, DD for day, etc.
Error handling in PureScript is typically done using the Either type, which we pattern match on to handle success and error cases.
PureScript doesn’t have a direct equivalent to Go’s string formatting with Printf. Instead, we use the formatDateTime function with a custom format string to achieve similar results.

This example demonstrates how to perform time formatting and parsing in PureScript, covering the main concepts from the original example while adapting to PureScript’s functional paradigm and type system.

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Time Formatting Parsing in PureScript