-- Unison is a statically typed functional language

increment : Nat -> Nat -- signature is optional

increment n = n + 1

-- Lines starting with `>` are evaluated and printed on every file save.

> increment 99

replicate : Nat -> a -> [a]

replicate n a = toSequence (take n (constant a))

-- this is nice for quick testing!

> replicate 3 "bye"

-- can ask Unison for the type of any expression just by adding `?` to the end of it

-- > (replicate 4)?

-- here's a more interesting example, mergesort -

-- First we define the merge function, it merges two sorted lists

merge : (a -> a -> Boolean) -> [a] -> [a] -> [a]

merge lte a b =

use Sequence ++

use Optional None Some

go acc a b = match at 0 a with

None -> acc ++ b

Some hd1 -> match at 0 b with

None -> acc ++ a

Some hd2 ->

if hd1 `lte` hd2 then go (acc `snoc` hd1) (drop 1 a) b

else go (acc `snoc` hd2) a (drop 1 b)

go [] a b

-- let's make sure it works

> merge (<) [1,3,4,99,504,799] [0,19,22,23]

-- looks good, now let's write mergesort

sort : (a -> a -> Boolean) -> [a] -> [a]

sort lte a =

if Sequence.size a < 2 then a

else

l = sort lte (take (size a / 2) a)

r = sort lte (drop (size a / 2) a)

merge lte l r

-- let's make sure it works

> sort (<) [3,2,1,1,2,3,9182,1,2,34,1,80]

> sort (<) ["Dave", "Carol", "Eve", "Alice", "Bob", "Francis", "Hal", "Illy", "Joanna", "Greg", "Karen"]

-- SHIP IT!! 🚢

-- If you make a mistake, we try to have nice friendly error messages, not:

-- 🤖 ERROR DETECTED ⚡️ BEEP BOOP ⚡️ PLS RESUBMIT PROGRAM TO MAINFRAME

-- a few examples of failing programs -

--err1 =

-- a = "3"

-- sort (<) [1,2,a]

-- err1a = sort (<) "not a list"

--err2 : x -> y -> x

--err2 thing1 thing2 =

-- if true then thing1

-- else thing2