guibou

The jj default revset filter, present(@) | ancestors(immutable_heads().., 2) | present(trunk()) had been mysterious for me for multiples hours.

And frankly, I don't like things to be mysterious, at least in computer sciences (if you are a book, be misterious, that's great. If you are a date, well, don't force it, that's annoying. If you are a computer science date, you should not be mysterious at all. I see you, USA YY-DD-MM !)

The default log revset

guibou

ghci> duration @"P1Y1W"
Duration {years = 1, months = 0, days = 0, weeks = 1, hours = 0, minutes = 0, seconds = 0}
ghci> duration @"P1Y1WT10H5M"
Duration {years = 1, months = 0, days = 0, weeks = 1, hours = 10, minutes = 5, seconds = 0}
ghci> duration @"P1Y1WT10H5M120S"
Duration {years = 1, months = 0, days = 0, weeks = 1, hours = 10, minutes = 5, seconds = 120}
ghci> duration @"P10H5M120S"

<interactive>:119:1: error:
    • Cannot parse duration. Expecting 'T', got: 10H5M120S

guibou

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE GADTs #-}
import GHC.Generics
import Data.Data (Data, Typeable)
data Tag = TagA | TagB

data MyGADT t where

guibou

cases :: [a] -> String
cases _ = "Hello"

fiz = \cases l -> cases

main = do
  putStrLn $ fiz "Chien" []

guibou

locFromECP :: ECP -> PV SrcSpan
locFromECP e = locA . getLoc <$> unECP e

{-
1. Defined but not used: ‘locFromECP’
2. • Ambiguous type variable ‘t0’ arising from a use of ‘unECP’
     prevents the constraint ‘(DisambECP (t0 GhcPs))’ from being solved.
     Probable fix: use a type annotation to specify what ‘t0’ should be.
     These potential instances exist:
       instance DisambECP (PatBuilder GhcPs)

guibou

{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE BangPatterns #-}
import Control.Arrow

fact :: Int -> IO Int
fact = go 1
  where
    go acc 0 = pure acc
    go !acc n = do
      putStrLn "Yada"

guibou

{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE FlexibleInstances #-}
class Fold f t acc | f -> t acc where
  foldLR :: Foldable foldable => f -> acc -> foldable t -> acc

instance Fold (t -> acc -> acc) t acc where
  foldLR = foldr

instance Fold (acc -> t -> acc) t acc where

guibou

#include <iostream>

class Callback
{
    public:
    virtual void call() = 0;
};

Callback *registered_callback;

guibou

{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE FlexibleContexts #-}
{-# OPTIONS -Wall -Wredundant-constraints #-}

{-# LANGUAGE TypeFamilies #-}

{-# LANGUAGE ConstrainedClassMethods #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE DerivingVia #-}
{-# LANGUAGE UndecidableInstances #-}

guibou

{-# LANGUAGE TypeApplications #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE DerivingVia #-}
{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE ConstraintKinds #-}