Pattern matching in functional programming languages is a way to break up expressions into individual cases.

We are going to go through how to pattern match in PureScript with simple patterns, guards, array patterns and record patterns.

greater :: Int -> Int -> Int
greater n m | n > m = n -- '|' is called guard, the same as if else
| otherwise = m isEmpty :: forall a. Array a -> Boolean -- a in array should have same type
isEmpty [] = true
isEmpty _ = false
main = render =<< withConsole do
log $ show $ greater 3 2 -- 3
log $ show $ greater 11 22 -- 22
log $ show $ isEmpty [] -- true
log $ show $ isEmpty [1, 2] -- false

--

Full code:

module Main where

import Prelude
import Control.Monad.Eff.Console (log)
import TryPureScript myTypes :: Int
myTypes = 1 -- add (a -> (b -> (a + b)))
add :: Int -> Int -> Int
add a b = a + b
addMe = \a -> \b -> a + b -- inc (a -> (add 1 a))
inc :: Int -> Int
inc = add 1 -- Data constructors
data FooType = Foo | Bar String runFoo :: FooType -> String
-- runFoo take a param Foo which should be string
runFoo Foo = "it is foo"
-- runFoo also can take Bar and String
-- <> is similar to str.concat isn JS
runFoo (Bar s) = "Yeah it's Bar and " <> s greater :: Int -> Int -> Int
greater n m | n > m = n -- '|' is called guard, the same as if else
| otherwise = m isEmpty :: forall a. Array a -> Boolean -- a in array should have same type
isEmpty [] = true
isEmpty _ = false main = render =<< withConsole do
log $ show $ greater 3 2
log $ show $ greater 11 22
log $ show $ isEmpty []
log $ show $ isEmpty [1, 2]

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