FrigoEU

Pretty Printing Ur
  Ur Definition Rules
    val -> Ur Expression Rules
    fun so align arguments and result -> Ur Expression Rules
    comments -> Comment Rules
  Ur Expression Rules
    let -> Let Binding Rules
    case of so pretty print -> Ur Expression Rules
    Open angular brackets -> XML Tag Rules
    Open Xml Tags -> XML Content Rules

FrigoEU

Parsing CSV
  New Line*
    EOF -> Done
    Not EOF -> Reading Field
  Reading Field
    EOF -> Not Quoted
    First character is quote -> Quoted
    First character is not quote -> Not Quoted
  Quoted
    Read till next quote and use as value -> After Quoted

FrigoEU

Import Screen
  Not Yet Imported*
    Initial
      import is ok -> Imported
      wrong format -> Display Error
    Display Error
      import is ok -> Imported
      wrong format -> Display Error
  Imported
    No Errors

FrigoEU

Getting good error messages when the compiler rejects your program is very important for the day to day usability of a language. In an attempt to allow library authors to help out with this and generate better error messages for their users, the ability to define "Fail" instances for typeclasses was added to the compiler in v0.9.1. When a user of a typeclass tries to use one of these instances, the compiler will throw a custom error. Which error depends on how you define your Fail instance. For example:

module Main where

import Prelude
import Control.Monad.Eff.Console (log)

class Serialize a where
 serialize :: a -> String

FrigoEU

module Main where

import Prelude
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, log, logShow)
import Data.Newtype (class Newtype, unwrap)
import Data.Profunctor (dimap)
import Data.Profunctor.Strong (class Strong, second)
import Data.Tuple (Tuple(..), uncurry)
import Type.Proxy (Proxy(..))

FrigoEU

module Main where

import Prelude
import Control.Monad.Eff.Console (log)

class Serialize a where
  serialize :: a -> String

instance cannotSerializeFunctions 
    :: Fail ("Cannot serialize the function: " <> TypeString (a -> b) <> ". Functions can't be serialized.") 

FrigoEU

module Main where

import Prelude
import Control.Monad.Eff.Console (log)

class Serialize a where
  serialize :: a -> String

instance cannotSerializeFunctions 
    :: Fail ("Cannot serialize functions.") 

FrigoEU

module Lovefield where

import Data.Array (snoc)
import Data.Foreign (Foreign)
import Data.Lens (Lens, lens)
import Data.Tuple (Tuple(..))
import Prelude (class Show, show, (#), ($), (<>), (>>>))

-- Your implementation of polymorphic labels starts here
data Label (l :: Symbol) = Label

FrigoEU

manyMaybe :: forall m a. (Monad m) => ParserT String m a -> ParserT String m (Array a)
manyMaybe p = mapMaybe id <$> many (maybeP p)

maybeP :: forall m a. (Monad m) => ParserT String m a -> ParserT String m (Maybe a)
maybeP p = choice [(Just <$> p), (anyChar *> return Nothing)]

FrigoEU

url :: URL
arr = [maybe mempty (\o -> Node.SimpleRequest.host := o) (toMaybe url.host), ...]
opt = foldMap id arr