DEV Community

loading...

Format Date with Purescript

Moremi Vannak
Enthusiastic Functional Programmer, specialized in Haskell, Purescript, Elm...
・2 min read

This will be a simple tutorial on how to parse date with purescript using purescript-formatters. I will use date from postgres: 2018-09-30T12:27:33.168791 as the example

We will need two functions one that will convert string to datetime and another will display that datetime value.

parseDate :: String -> Either DateTime
displayDate :: DateTime -> String
Enter fullscreen mode Exit fullscreen mode

We will need 2 formatters for both decode and display:

parseFormatter :: Formatter
parseFormatter =  unsafePartial fromRight $  parseFormatString "YYYY-MM-DDTHH:mm:ss"

displayFormatter :: Formatter
displayFormatter =  unsafePartial fromRight $  parseFormatString "hh:mm:ss, DD MMM YYYY"
Enter fullscreen mode Exit fullscreen mode

Then we can use this formatter in our previous functions

parseDate :: String -> Either String DateTime
parseDate s = 
    unformat parseFormatter s

displayDate :: DateTime -> String
displayDate d = 
    format displayFormatter d
Enter fullscreen mode Exit fullscreen mode

We can combine them together

parseAndDisplay :: String -> String
parseAndDisplay s = 
    either (\err -> err) (\d -> displayDate d) $ parseDate s
Enter fullscreen mode Exit fullscreen mode

If you run this, you may have noticed a run time error. Because our seconds is in fraction. We do not need that so we can just drop them off.

parseAndDisplay :: String -> String
parseAndDisplay s = 
    either (\err -> err) (\d -> displayDate d) $ parseDate $ String.take 19 s
Enter fullscreen mode Exit fullscreen mode

If you run this with input 2018-09-30T12:27:33.168791, you will get 12:27:33, 30 Sep 2018

There you go here is the full code

import Prelude 

import Data.Either (Either, either, fromRight)
import Data.String as String
import Data.DateTime (DateTime)

import Data.Formatter.DateTime (Formatter, parseFormatString, unformat, format)
import Partial.Unsafe (unsafePartial)

parseFormatter :: Formatter
parseFormatter =  unsafePartial fromRight $ parseFormatString "YYYY-MM-DDTHH:mm:ss"

displayFormatter :: Formatter
displayFormatter =  unsafePartial fromRight $ parseFormatString "hh:mm:ss, DD MMM YYYY"

parseDate :: String -> Either String DateTime
parseDate s = 
    unformat parseFormatter s

displayDate :: DateTime -> String
displayDate d = 
    format displayFormatter d

parseAndDisplay :: String -> String
parseAndDisplay s = 
    either (\err -> err) (\d -> displayDate d) $ parseDate $ String.take 19 s
Enter fullscreen mode Exit fullscreen mode

Discussion (2)

Collapse
tbm206 profile image
Taha Ben Masaud

Excellent. Thank you

Collapse
piq9117 profile image
Ken Aguilar

Yo! thanks for this. I've been having trouble manipulating DateTime. This article showed me that I can use ParserT/Parser

Forem Open with the Forem app