Hello
Here is the latest Caml Weekly News, for the week of June 19 to 26, 2007.
I'm pleased to announce an initial release of `deriving', a system for
constructing functions automatically from type definitions.
Deriving extends OCaml with two new operations: a syntax for calling
an "overloaded" function at a particular type:
C.function<t> v
and the `deriving' construct found in Haskell (and Clean) for
requesting that the implementation generate an instance of an
overloaded function from a type definition:
type t = r
deriving (C1, C2)
Deriving provides functions for pretty-printing, dynamic typing,
type-safe structure-sharing marshalling, SML-style equality,
mapping, and more. Functions can be generated for most OCaml types,
including records, standard and polymorphic variants, tuples, mutually
recursive types, and types that use abstract type constructors defined
elsewhere. A few more exotic constructs, such as private types and type
replication, are supported. Derived functions are also extensible: the
user can choose to supply an implementation at a particular type if the
generated version is not to his taste.
You can find deriving (along with preliminary documentation and tests)
at
http://code.google.com/p/deriving/
Note: you'll need OCaml 3.10.
Some examples of use follow.
Pretty-printing:
Show.show<int> 3
=>
"3"
let factors = [(10,[2;5]); (11, []); 12, [2;3;4;6]]
Show.show<(int * int list) list> factors
=>
"[(10,[2; 5]); (11, []); 12, [2; 3; 4; 6]]"
type 'a tree = Leaf of 'a | Branch of 'a tree * 'a * 'a tree
deriving (Show, Typeable, Eq, Shelve)
type point = { x : float; y : float }
deriving (Show, Typeable, Eq, Shelve)
let points = Branch (Leaf {x=0.0;
y=0.0;},
{x=2.0; y=2.0},
Branch (Leaf {x=1.0; y=1.0},
{x=1.0; y=0.0},
Leaf {x=0.0; y=1.0}))
Show.show<point tree> points
=>
"Branch
(Leaf {x =193.11; y =132.13}, {x =211.91; y =201.11},
Branch
(Leaf {x =113.12; y =1.}, {x =12.7; y =44.1}, Leaf {x =0.; y =13.41}))"
Dynamic typing:
let items =
[Typeable.mk<int> 3;
Typeable.mk<float> 3.0;
Typeable.mk<string tree> (Leaf "three")]
=>
[<abstr>; <abstr>; <abstr>]
Typeable.cast<int> (List.hd items)
=>
Some 3
Typeable.cast<float> (List.hd items)
=>
None
Dynamic typing again:
type 'a seq = [`Nil | `Cons of 'a * 'a seq]
deriving (Typeable)
let l = `Cons (3, `Cons (2, `Cons (1, `Nil)))
Typeable.cast<[`Cons of int * 'a|`Nil] as 'a>
(Typeable.mk<int seq> l)
=>
Some (`Cons (3, `Cons (2, `Cons (1, `Nil))))
Serialisation (marshalling):
Shelve.shelveS<point tree> points
=>
"\007\003\t\128\128\128\128\128\128\128\248?\t\128\128\128\128\128\128\128\128@\001\000\005\000\001\008\000\001\n\001\003\004\t\003\000\001\012\001\003\006\011\005\005\002\002\000\002\000\002\002\000\000\002\001\001\002\002\002"
Shelve.unshelveS<point tree> (Shelve.shelveS<point tree> points)
=>
Branch
(Leaf {x =193.11; y =132.13}, {x =211.91; y =201.11},
Branch
(Leaf {x =113.12; y =1.}, {x =12.7; y =44.1}, Leaf {x =0.;
y =13.41}))
Shelve.unshelveS<int> (Shelve.shelveS<point tree> points)
=>
*** Exception
For more see the documentation and test suite.
Comments, bug reports, and other feedback will be most welcome.
If ever you are interested in putting some caml code inside your latex
document, *without* using verbatim environment or listings package,
the online tool :
http://philippewang.info/cs.tools.camltotex.php (*)
takes some caml code and returns LaTeX code.
The applied treatments are :
- colors
- nested comments (even with strings such as "*)" inside) are detected
- based on LaTeX macros such as
\DeclareTextSymbol{\BS}{T1}{92} % backslash
\newcommand{\mlkeyword}[1]{\mbox{\color{red}{#1}}}
- the code is put in a tabular environment
Well, it's very small : 300 lines of code for the moment (about 230
lines of ocamllex and 30 lines of ocaml...).
It could have certainly been written in camlp4 or in latex, but well,
they are not (yet) my cup of tea.
Hopefully, it will be released under a free license next month (if you
are interested in this program, which license do you want ?)
The main goals are :
- no use of verbatim, so that it can be used with beamer without the
[fragile] option
- no use of the listings package (because it don't like it)
It certainly contains bugs, it was never proved or certified, and
probably never will be...
Cheers,
--
Philippe Wang
mail[at]philippewang.info
(*) I used php because cgi in pure caml is very complicated on the
hosting server
Announcing graph, a utility to print a pretty graph of a time series in an ansi terminal. http://homepage.mac.com/letaris its in godi :-)
Here is a quick trick to help you read this CWN if you are viewing it using vim (version 6 or greater).
:set foldmethod=expr
:set foldexpr=getline(v:lnum)=~'^=\\{78}$'?'<1':1
zM
If you know of a better way, please let me know.
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