Re: [Haskell-cafe] Definition of List type?

Ben Millwood wrote:

On Fri, Jul 30, 2010 at 7:50 PM, Gregory Crosswhite wrote:

...

The reason why this definition never actually appears is because it defines the constructors using operators rather than names, which is not allowed in vanilla Haskell. (There is an extension, TypeOperators, however, that does allow this.)

Nope: see Data.Complex.Complex; only infix *type* constructors are nonstandard. The thing about lists that makes them impossible to define in normal Haskell is the [a] syntax, which is some kind of "outfix" type constructor, which no amount of currently available extensions will allow.

It's normally called "confix" or "circumfix". Similarly, the tuple syntaxes can't be defined in Haskell because they use "mixfix" notation (which apparently some folks call "distfix"[1]). Also, lists support a mixfix sugar where [a,b,...,c] = a:b:...:c:[] Agda does support full mixfix notation. While it's nice in theory, when combined with the verbosity of dependently typed languages it gets illegible pretty quickly for the uninitiated. [1] http://github.com/noteed/syntactical -- Live well, ~wren