Switch in Idris

Here’s the translation of the given code into Idris along with an explanation.

Switch statements express conditionals across many branches.

module Main

import Data.Time

main : IO ()
main = do
    let i = 2
    putStr("Write " ++ show i ++ " as ")
    case i of
        1 => putStrLn "one"
        2 => putStrLn "two"
        3 => putStrLn "three"
        _ => pure ()

    -- Using multiple expressions in the same case statement and a default case
    currentTime <- getCurrentTime
    let weekday = dayOfWeek (toCalendarTime (UTCTime currentTime))
    case weekday of
        Saturday, Sunday => putStrLn "It's the weekend"
        _ => putStrLn "It's a weekday"

    -- Switch without an expression, using non-constant expressions in case statements
    let hour = timeOfDayHour (timeToTimeOfDay (utctDayTime currentTime))
    case () of
        _ | hour < 12 => putStrLn "It's before noon"
        _ => putStrLn "It's after noon"

    -- Type switch to determine the type of an interface value
    whatAmI : (input : Type) -> IO ()
    whatAmI t = case t of
        Bool t => putStrLn "I'm a bool"
        Int t => putStrLn "I'm an int"
        _ => putStrLn ("Don't know type " ++ show t)

    whatAmI True
    whatAmI 1
    whatAmI "hey"

Here’s a basic case.

    let i = 2
    putStr("Write " ++ show i ++ " as ")
    case i of
        1 => putStrLn "one"
        2 => putStrLn "two"
        3 => putStrLn "three"
        _ => pure ()

You can use commas to separate multiple expressions in the same case statement. We use the optional default case in this example as well.

    currentTime <- getCurrentTime
    let weekday = dayOfWeek (toCalendarTime (UTCTime currentTime))
    case weekday of
        Saturday, Sunday => putStrLn "It's the weekend"
        _ => putStrLn "It's a weekday"

case without an expression is an alternate way to express if/else logic. Here we also show how the case expressions can be non-constants.

    let hour = timeOfDayHour (timeToTimeOfDay (utctDayTime currentTime))
    case () of
        _ | hour < 12 => putStrLn "It's before noon"
        _ => putStrLn "It's after noon"

A type case compares types instead of values. You can use this to discover the type of an interface value. In this example, the variable t will have the type corresponding to its clause.

    whatAmI : (input : Type) -> IO ()
    whatAmI t = case t of
        Bool t => putStrLn "I'm a bool"
        Int t => putStrLn "I'm an int"
        _ => putStrLn ("Don't know type " ++ show t)

    whatAmI True
    whatAmI 1
    whatAmI "hey"

Running the code will produce the expected outputs based on the conditions specified.

If Else in Idris

Arrays in Idris

Learn X By Example

Title here

Switch in Idris