purescript

Pros of Elm compiler

• Simpler language with a gentler learning curve
• Strong focus on developer experience and friendly error messages
• Enforces a more opinionated architecture, leading to consistent codebases

Cons of Elm compiler

• Less flexible and expressive compared to PureScript
• Smaller ecosystem with fewer libraries and tools
• Limited interoperability with JavaScript

Code comparison

Elm:

module Main exposing (main)

import Browser
import Html exposing (Html, button, div, text)
import Html.Events exposing (onClick)

main =
  Browser.sandbox { init = 0, update = update, view = view }

update msg model =
  case msg of
    Increment -> model + 1
    Decrement -> model - 1

view model =
  div []
    [ button [ onClick Decrement ] [ text "-" ]
    , div [] [ text (String.fromInt model) ]
    , button [ onClick Increment ] [ text "+" ]
    ]

PureScript:

module Main where

import Prelude
import Effect (Effect)
import Halogen as H
import Halogen.HTML as HH
import Halogen.HTML.Events as HE

data Action = Increment | Decrement

component :: forall q i o m. H.Component q i o m
component =
  H.mkComponent
    { initialState: const 0
    , render
    , eval: H.mkEval $ H.defaultEval { handleAction = handleAction }
    }

render :: forall m. Int -> H.ComponentHTML Action () m
render state =
  HH.div_
    [ HH.button [ HE.onClick \_ -> Decrement ] [ HH.text "-" ]
    , HH.div_ [ HH.text $ show state ]
    , HH.button [ HE.onClick \_ -> Increment ] [ HH.text "+" ]
    ]

handleAction :: forall o m. Action -> H.HalogenM Int Action () o m Unit
handleAction = case _ of
  Increment -> H.modify_ (_ + 1)
  Decrement -> H.modify_ (_ - 1)

Pros of Idris2

• Dependent types allow for more expressive and precise type-level programming
• Totality checking ensures all functions terminate, improving program correctness
• Supports interactive theorem proving, enabling formal verification of code

Cons of Idris2

• Smaller community and ecosystem compared to PureScript
• Steeper learning curve due to advanced type system features
• Potentially slower compilation times for complex dependent type programs

Code Comparison

Idris2:

factorial : Nat -> Nat
factorial 0 = 1
factorial n = n * factorial (n - 1)

-- Proof that factorial is always positive
factorialPositive : (n : Nat) -> LT 0 (factorial n)
factorialPositive 0 = LTESucc LTEZero
factorialPositive (S k) = LTESucc (multLTELeft (S k) (factorial k) (factorialPositive k))

PureScript:

factorial :: Int -> Int
factorial 0 = 1
factorial n = n * factorial (n - 1)

-- No built-in support for theorem proving
-- Type-level programming is possible but less expressive

The code comparison showcases Idris2's ability to include proofs within the code, demonstrating its dependent type system and theorem-proving capabilities. PureScript, while powerful, lacks these advanced features but offers a more familiar and approachable syntax for functional programming.

Pros of Agda

• More powerful type system with dependent types
• Stronger focus on theorem proving and formal verification
• Closer integration with mathematical concepts and proofs

Cons of Agda

• Steeper learning curve and more complex syntax
• Smaller ecosystem and fewer libraries
• Less focus on practical application development

Code Comparison

Agda:

data Vec (A : Set) : ℕ → Set where
  []  : Vec A zero
  _∷_ : ∀ {n} → A → Vec A n → Vec A (suc n)

head : ∀ {A n} → Vec A (suc n) → A
head (x ∷ _) = x

PureScript:

data Vec a = Nil | Cons a (Vec a)

head :: forall a. Vec a -> Maybe a
head Nil = Nothing
head (Cons x _) = Just x

The Agda example showcases its dependent types, allowing for precise length specification in the vector type. PureScript's version is simpler but less type-safe, using Maybe for potential empty vectors.

Agda excels in formal verification and theorem proving, while PureScript is more suited for practical functional programming in web development. Agda's type system is more expressive but comes with increased complexity, whereas PureScript offers a balance between strong typing and ease of use.

Pros of OCaml

• Mature ecosystem with a long history and extensive standard library
• Strong support for systems programming and native code compilation
• Powerful module system for large-scale software engineering

Cons of OCaml

• Steeper learning curve, especially for developers new to functional programming
• Less focus on web development and JavaScript interoperability
• Smaller community compared to more mainstream languages

Code Comparison

OCaml:

let rec factorial n =
  if n = 0 then 1
  else n * factorial (n - 1)

let result = factorial 5

PureScript:

factorial :: Int -> Int
factorial 0 = 1
factorial n = n * factorial (n - 1)

result = factorial 5

Summary

OCaml is a mature, statically-typed functional language with a focus on systems programming and native compilation. It offers a powerful module system and extensive standard library. PureScript, on the other hand, is designed for web development with JavaScript interoperability in mind. It has a more approachable syntax for developers coming from JavaScript backgrounds.

While OCaml excels in systems programming and large-scale software engineering, PureScript shines in web development scenarios. OCaml has a steeper learning curve but offers more low-level control, whereas PureScript provides a gentler introduction to functional programming for web developers.

Both languages share similar functional programming concepts, as seen in the factorial example, but differ in their syntax and ecosystem focus.

Pros of GHC

• Mature and widely-used compiler for Haskell, with extensive ecosystem support
• Highly optimized runtime system for efficient execution of Haskell programs
• Supports a broader range of language extensions and features

Cons of GHC

• Larger codebase and more complex architecture, making it harder to contribute
• Slower compilation times, especially for large projects
• Steeper learning curve for newcomers to the Haskell ecosystem

Code Comparison

PureScript (simplified example):

module Main where

import Effect.Console (log)

main :: Effect Unit
main = log "Hello, PureScript!"

GHC Haskell (simplified example):

module Main where

main :: IO ()
main = putStrLn "Hello, Haskell!"

Summary

GHC is a more established and feature-rich compiler for Haskell, offering advanced optimizations and a wide range of language extensions. However, it comes with increased complexity and longer compilation times. PureScript, while younger and less feature-rich, offers a more approachable system with faster compilation and a focus on JavaScript interoperability. The code examples demonstrate the similarity in syntax between the two languages, with PureScript's additional type annotations for effects.

Pros of Reason

• Easier learning curve for developers familiar with JavaScript
• Better integration with existing JavaScript ecosystems and tooling
• Faster compilation times for large projects

Cons of Reason

• Smaller community and ecosystem compared to PureScript
• Less emphasis on advanced functional programming concepts
• More limited type system compared to PureScript's expressive types

Code Comparison

Reason:

let add = (a, b) => a + b;
let result = add(5, 3);
Js.log("Result: " ++ string_of_int(result));

PureScript:

add :: Int -> Int -> Int
add a b = a + b

main :: Effect Unit
main = do
  let result = add 5 3
  log $ "Result: " <> show result

Both languages aim to provide a statically-typed functional programming experience for web development. Reason focuses on accessibility and JavaScript interoperability, while PureScript emphasizes purity and advanced type system features. Reason may be more appealing to developers transitioning from JavaScript, while PureScript might attract those seeking a more rigorous functional programming experience.