Elm:
Parsing a date from a string

How to:

Elm does not have built-in capabilities as robust as some other languages for date parsing, primarily relying on Javascript interop or libraries for more complex operations. However, you can use the elm/time package for basic parsing, and for more complex needs, the third-party justinmimbs/date library is widely recommended.

Parsing using elm/time:

elm/time provides the Time module, which allows you to work with timestamps instead of human-readable dates. While it does not directly parse dates from strings, you can convert an ISO 8601 string into a POSIX timestamp, which you can then work with.

import Time exposing (Posix)

-- Assuming you have an ISO 8601 date string
isoDateStr : String
isoDateStr = "2023-01-01T00:00:00Z"

-- Convert it to a POSIX timestamp (this function returns a `Result`)
parsedDate : Result String Posix
parsedDate = Time.fromIsoString8601 isoDateStr

-- Sample output: Ok <posix time value>

Parsing using justinmimbs/date:

For more intricate parsing, like dealing with non-ISO formats, justinmimbs/date library is a great choice. Here’s how you can use it to parse a custom date string:

1. Ensure you have the library installed:

elm install justinmimbs/date

2. Use the Date.fromString function to parse custom date formats:

import Date
import Result exposing (Result(..))

-- Let's say you have a custom date string format `dd-MM-yyyy`
customDateStr : String
customDateStr = "01-01-2023"

-- Function to parse the custom format
parseDate : String -> Result String Date.Date
parseDate = Date.fromString "dd-MM-yyyy"

-- Sample usage
parsedCustomDate : Result String Date.Date
parsedCustomDate = parseDate customDateStr

-- Sample output: Ok (Date.fromCalendarDate 2023 Jan 1)

In these examples, the Result type encapsulates either a successful parsing that yields a date (Ok) or an error (Err), enabling robust error handling in your Elm applications.