I once stumbled upon the following. Answering this question, I first tried this code: {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FunctionalDependencies #-} class (Eq a, Show a) => Genome a where crossover :: (Fractional b) => b -> a -> a -> IO (a, a) mutate :: (Fractional b) => b -> a -> IO … Read more
It’s a gcc-specific extension, a unary && operator that can be applied to a label name, yielding its address as a void* value. As part of the extension, goto *ptr; is allowed where ptr is an expression of type void*. It’s documented here in the gcc manual. You can get the address of a label … Read more
An ad hoc list of morally “good” extensions, and morally “bad” ones – this is an aesthetic judgement! The Good GADTs Parallel list comprehensions Pattern guards Monad comprehensions Tuple sections Record wild cards Empty data decls Existential types Generalized new type deriving MPTCs + FDs Type families Explicit quantification Higher rank polymorphism Lexically scoped tyvars … Read more
It’s deprecated because it was a misfeature, and didn’t actually have any useful functionality! All it did was force a bunch of extra constraints in other locations. In particular, when pattern matching on such a type, you’d be forced to add a constraint, rather than (as one might initially hope) get access to a context, … Read more
It assigns user input value to a and prints it out. it is done by using a Statement Expression. Statement Expressions are a gnu gcc compiler extension and are not supported by the C/C++ standards. Hence, any code which uses statement expression is not standard conforming and non-portable. The IBM XL C/C++ v7.0 also support … Read more
C++ Modules draft (Technical Specification after C++17) A draft and several updated revisions for the C/C++ module specification have been published by WG21 on open-std.org. I will link only to the latest documents here: Working Draft, Extensions to C++ for Modules N4610 (October 2016). Fourth revision published as P0142R0 (March 2016). Wording for Modules published … Read more
:set -XRankNTypes. The -X part is a compiler switch, by the way, extension is called just RankNTypes.