Version française
Home     About     Download     Resources     Contact us    
Browse thread
what do I need to know to understand camlp4
[ Home ] [ Index: by date | by threads ]
[ Search: ]

[ Message by date: previous | next ] [ Message in thread: previous | next ] [ Thread: previous | next ]
Date: -- (:)
From: Elias Gabriel Amaral da Silva <tolkiendili@g...>
Subject: Re: [Caml-list] what do I need to know to understand camlp4
2010/9/23 ben kuin <benkuin@gmail.com>:

>> [1] Compared to other programming languages. I know the syntax is > the way it is for precise reasons (currying, closer to mathematical
>> notation, ...).
> Would you mind to list a few mathematical subjects that help me to
> understand OCamls syntax?

I suppose one is lambda calculus. Function application is
left-associative in ML. That is, if $ is an operator such as a $ b
means "a applied to b", then it is more natural to interpret a $ b $ c
as (a $ b) $ c[1]. The apply "operator" is simply not written in
OCaml, so we write just a b c, and it means (a b) c.

This is due to the fact that a N parameter function is just a
single-parameter function that return a new "curried" function that
gets N-1 parameters - just like lambda calculus. So one could write
let f = a b in f c to make this explicit as well. (This gets a bit
more complicated with optional parameters)

In fact, you want some mathematical background on functional
programming aesthetics (and whatnot),
http://en.wikipedia.org/wiki/Lambda_calculus may be a good
introduction.

[1] Pervasives should define it. In fact, even though ** is
right-associative, it looks like any user-defined operator is
left-associative by default. So it works like Haskell:

# let ($) a b = a b;;
val ( $ ) : ('a -> 'b) -> 'a -> 'b = <fun>
# fun x y z -> x $ y $ z;;
- : ('a -> 'b -> 'c) -> 'a -> 'b -> 'c = <fun>
# let q = fun x y z -> x $ y $ z;;
val q : ('a -> 'b -> 'c) -> 'a -> 'b -> 'c = <fun>
# let q' = fun x y z -> (x $ y) $ z;;
val q' : ('a -> 'b -> 'c) -> 'a -> 'b -> 'c = <fun>
# let q'' = fun x y z -> x $ (y $ z);;
val q'' : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'b = <fun>
# let q''' = fun x y z -> x $ y z;;
val q''' : ('a -> 'b) -> ('c -> 'a) -> 'c -> 'b = <fun>

-- 
Elias Gabriel Amaral da Silva <tolkiendili@gmail.com>