Re: Metaprogramming in D : Some Real-world Examples
Hello Lutger, Walter Bright wrote: Looks like Bill Baxter is giving a presentation on D Nov. 18! http://www.nwcpp.org/ slides are there! Very pretty, I bet it was a fine presentation. The slides are informative, good examples. re: the slides, are they avalable in .ppt or pdf for us ludites?
Re: Metaprogramming in D : Some Real-world Examples
nice work
Re: Metaprogramming in D : Some Real-world Examples
Bill Baxter wbax...@gmail.com wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
I've use the code below to generate wrappers for my hessian serialization
implementation.
its not all absolutely necessary but is only 130 lines.
import std.stdio;
import std.typetuple;
import std.traits;
import std.metastrings;
string[] splitFuncs(string str) {
string[] res;
while (str.length 0) {
while (str.length 0 (' ' == str[0] || ',' == str[0])) {
str = str[1..$];
}
int to = 0;
for (; to str.length str[to] != ' ' str[to] != ','; ++to) {}
if (to 0) {
res ~= str[0..to];
str = str[to..$];
}
}
return res;
}
string MethodTypeTuple_mixin(alias a)(string[] methods) {
string ret = TypeTuple!(~ typeof(C.init.~methods[0]~);
foreach (method; methods[1..$]) {
ret ~= ,typeof(C.init.~method~);
}
ret ~= );
return ret;
}
// test case
class A {
int a;
this(int a) {
this.a = a;
}
int getInt(string intname) {
return a;
}
void setInt(int i) {
a = i;
}
string getString(string s) {
return s ~1234;
}
}
string ProxyMethods_mixin(alias C, string methodstr)() {
string ret;
foreach(i, t; mixin(MethodTypeTuple_mixin!(C)(splitFuncs(methodstr {
// output function header
ret ~= \t~ReturnType!(t).stringof ~ ~
splitFuncs(methodstr)[i]~(;
// output first arg
ret ~= ParameterTypeTuple!(t)[0].stringof~ arg;
// output remainder of args
foreach (j, t1; ParameterTypeTuple!(t)[1..$]) {
ret ~= ,~t1.stringof~
arg~std.metastrings.ToString!(j);
}
// output body
ret ~= ) {\n;
// output serialization code
// send method name
ret ~= \t\twritefln(\serialize docall id\); // the method
call byte
id\n;
ret ~=
\t\t//serialize!(string)(\~splitFuncs(methodstr)[i]~\); /+
the method name +/\n;
// send args
ret ~= \t\t//serialize!(~
ParameterTypeTuple!(t)[0].stringof~)
(arg); /+ the first argument +/\n;
foreach (j, t1; ParameterTypeTuple!(t)[1..$]) {
ret ~= \t\t//serialize!(~ t1.stringof
~)(arg~ToString!(j)~); /
+ argument ~ToString!(j)~ +/\n;
}
// receive return type
static if (!is(ReturnType!(t) == void)) {
pragma(msg, WARNING: this will always result in Range
violation
due to no real data. THIS IS JUST A DEMO);
pragma(msg, \t\t need to implement the actual
send/receive);
ret ~= \t\t//return deserialize!(~
ReturnType!(t).stringof ~)
(buffer);\n;
// this is just here to make it still compile even
though I've
commented out the real deserialize return above
static if (is(ReturnType!(t) == int)) {
ret ~= \t\treturn 0;\n;
} else {
ret ~= \t\treturn \\;\n;
}
}
ret ~= \t}\n;
}
return ret;
}
string ProxyClass_mixin(alias C, string methodstr)() {
string ret = new class { ubyte[] buffer;\n;
ret ~= ProxyMethods_mixin!(C, methodstr)();
ret ~= }\n;
pragma(msg, MethodTypeTuple_mixin!(C)(splitFuncs(methodstr)));
return ret;
}
class ProxyClass(alias C, string methodstr) {
ubyte[] buffer;
this() { }
mixin(ProxyMethods_mixin!(C,methodstr)());
}
/+ void serialize(T)(T value) {
writefln(serialize);
}
T deserialize(T)() {
writefln(deserialize);
static if (is(T==int)) {
return 1;
} else
return asdf;
} +/
void main() {
pragma(msg, ProxyClass_mixin!(A,cast(string)getInt setInt)());
Re: Metaprogramming in D : Some Real-world Examples
On Fri, Nov 13, 2009 at 11:38 AM, Tomas Lindquist Olsen
tomas.l.ol...@gmail.com wrote:
On Thu, Nov 12, 2009 at 8:24 PM, Bill Baxter wbax...@gmail.com wrote:
On Thu, Nov 12, 2009 at 10:46 AM, Tomas Lindquist Olsen
tomas.l.ol...@gmail.com wrote:
On Tue, Nov 10, 2009 at 1:27 AM, Bill Baxter wbax...@gmail.com wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
I think tuples are a good example of something that makes your life
easier, lately I've been very fond of this little snippet:
void delegate() Bind(Args...)(void delegate(Args) dg, Args args)
{
struct Closure
{
Args arguments;
void delegate(Args) callee;
void call()
{
callee(arguments);
}
}
auto c = new Closure;
// foreach not strictly necessary, but ldc currently chokes on
just an assignment... I should fix that..
foreach(i,a;args)
c.arguments[i] = a;
c.callee = dg;
return c.call;
}
class C
{
void foo(int,float) {}
}
void main()
{
auto c = new C;
auto dg = Bind(c.foo, 1, 2.0f);
// register delegate somewhere
}
Not sure if this gets easier in C++0x , haven't read up on that...
I think it does. C++0x has variadic templates. And some kind of
lambdas/closure thing. So probably it can do something similar.
Anyway, the meta- aspect of Bind seems kinda weak. Certainly a nice
use of variadic templates and closures, though.
--bb
Just read the Wikipedia entries on Metaprogramming and
Template_metaprogramming, I guess I wasn't really aware of the
difference.
Seems a lot harder to come up with small real-world snippets of the former.
The way I read it, template metaprogramming is a kind of
metaprogramming. Metaprogramming using templates.
And ctfe/string-mixin metaprogramming are another, macro
metaprogramming another etc.
I think the phrase template metaprogramming just took particularly
strong hold because of C++ where templates are always required for
accomplishing pretty much any kind of metaprogramming.
--bb
Re: Metaprogramming in D : Some Real-world Examples
On Mon, Nov 9, 2009 at 6:03 PM, Andrei Alexandrescu seewebsiteforem...@erdani.org wrote: Bill Baxter wrote: On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright newshou...@digitalmars.com wrote: Looks like Bill Baxter is giving a presentation on D Nov. 18! http://www.nwcpp.org/ Yep, that's right, and I'd be quite grateful to you smart folks here if you could share your meta-programming favorites with me! If you've got a real-world example of meta-programming in D that you think is particularly handy, then please send it my way I'm looking for small-but-useful things that are easy to explain, and make something easier than it would be otherwise. Things like places where static if can save your butt, or loop unrolling, and passing code snippets to functions like in std.algorithm. Things like a compile-time raytracer or regexp parser (though quite cool!) are not what I'm after. Too involved for a short talk. --bb std.random has code that checks the parameters of a congruential RNG during compilation. That's also an example in TDPL. This looks good. Any chance you could send me the snippet of the book that explains the rationale for what constitutes proper linear congruential parameters? --bb
Re: Metaprogramming in D : Some Real-world Examples
2009/11/10 Denis Koroskin 2kor...@gmail.com:
On Tue, 10 Nov 2009 03:27:20 +0300, Bill Baxter wbax...@gmail.com wrote:
kprintf (a printf variant) in XoMB is a nice example imo. It accepts format
as a template parameter, doing all the checks at compile-time (and more).
http://github.com/xomboverlord/xomb-bare-bones/blob/6d924a9fd7cafe43aa50f38c0cd04c44187d4993/kernel/core/kprintf.d
Nice. 400 lines is a little long for this purpose, though. Maybe a
somewhat simplified version that just replaces {} with template args
would be good. I guess that's pretty much what std.metastrings.Format
does, just with %s instead of {}.
--bb
Re: Metaprogramming in D : Some Real-world Examples
On 11/11/09 17:58, grauzone wrote:
Andrei Alexandrescu wrote:
grauzone wrote:
Don wrote:
Christopher Wright wrote:
grauzone wrote:
You're not testing for types, you're testing if it compiles.
Inside the tested block of code, all sorts of things could go
wrong. You can't know if is(typeof(...)) really did what you
wanted, or if something broke.
You're testing, is everything inside that OK?. If you want to know
WHY it's wrong, you'd better make sure you're testing something simple.
Andrei's range lib uses it more in a way does this type support this
and that range interface?. Example:
http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L58
Then different isXxxRange are used by higher-order ranges in defining
refined interfaces depending on the interfaces offered by their inputs.
That means if one isXxxRange fails because the user maybe made a typo in
the needed range function, the code will silently do something else.
But my main problem is that the user just gets a does not match
template declaration compiler error when he messes up his range
interface. He's neither told that e.g. his range-related function
returns the wrong type, nor is there any other refined error message.
The check doesn't have to look like that. The check can be inside the
template with static if and you can have several checks for different
things and use static assert to output a error message that make sense.
Now what if we'd introduce some sort of interfaces for type checking at
compile time?
interface InputRange(T) {
void popFront();
bool empty();
T front();
}
struct MyRange : InputRange!(int) {
void popFront() { ... }
//compiler error goes here...
void empty() { ... }
int front() { ... }
}
(or something like this)
PS: there are two aspects to the problem: 1. even compile time duck
typing shares some of the problems of runtime duck typing, and 2.
utterly unhelpful error messages. If you wouldn't explicitly check the
interface with is(typeof()), the compiler's error messages would be even
worse because of 1.
I fail to see how that's terrible. I am very happy D has that feature
- no other statically-typed language has it, and it can be used to
great effect. Look e.g. at Chain:
http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L799
There, the uses of static if (is(...)) allow Chain to define as
capable an interface as its inputs allow.
Andrei
Re: Metaprogramming in D : Some Real-world Examples
Bill Baxter wbax...@gmail.com wrote in message news:mailman.337.1258023453.20261.digitalmars-d-annou...@puremagic.com... Hi Nick, Thanks for the response. More below. However, the unescape() function used in traceVal looks like it might be a useful CTFE example. Some kind of compile-time string escaping/unescaping could definitely be a good example. Heh, I tend to forget about that one. That's from the semitwist.util.text module, which I haven't worked with much in a long time, so there's probably a lot of WTFs spread through the module, and if you use something there as an example, you might need to clean it up a little. FWIW, that double-quote-string escaping/unescaping is built around ctfe_substitute which is in semitwist.util.ctfe (although Tango might have something similar by now). [various] This is another one that C++ people would just throw macros at and wonder what the big deal is. Ah, yea, good point. Of course, we'd probably all take D's metaprogramming over preprocessor macros anyday, but I can definitely see their point. === Compile-time checking on types with non-identifier strings === That is kinda neat, I suppose you could even extend that to make the list of valid tokens be a template parameter (either variadic, or separated by some delimiter in one big string that then gets broken up at runtime). I guess you could pitch this as a baby step towards the full-fledged compile-time parser. Step 0 recognize valid tokens. Interesting idea, yea. Might not be much help for the lib as I currently have it though, since I'm just spitting out the static-style language definitions from a tool that takes in a grammar and generates D code. Certainly something to keep in mind for future expansion though. Thanks for writing all these up. No prob! :)
Re: Metaprogramming in D : Some Real-world Examples
Nick Sabalausky a...@a.a wrote in message
news:hdgt9q$vt...@digitalmars.com...
Bill Baxter wbax...@gmail.com wrote in message
news:mailman.337.1258023453.20261.digitalmars-d-annou...@puremagic.com...
Hi Nick,
=== Compile-time checking on types with non-identifier strings ===
That is kinda neat, I suppose you could even extend that to make the
list of valid tokens be a template parameter (either variadic, or
separated by some delimiter in one big string that then gets broken up
at runtime). I guess you could pitch this as a baby step towards the
full-fledged compile-time parser. Step 0 recognize valid tokens.
Interesting idea, yea. Might not be much help for the lib as I currently
have it though, since I'm just spitting out the static-style language
definitions from a tool that takes in a grammar and generates D code.
Certainly something to keep in mind for future expansion though.
One other idea I had for expanding on that NewStyle_StaticToken would be:
Suppose a grammar had some sort of naming convention that, well, meant
something within the context of that grammar. Then the application code
could take something like process(Token!(foo) token) {...} and use
compile-time string processing to do advanced pattern-matching on the
token-name when selecting which token types to process a certain way (maybe
it would have to be a static if or a templated instead of a basic function
though). Not a fully fleshed-out idea, of course, but maybe the start of
something. In fact, I think tango.util.Convert does something vaguely like
that to look for conversion functions.
Re: Metaprogramming in D : Some Real-world Examples
Andrei Alexandrescu wrote:
grauzone wrote:
Don wrote:
Christopher Wright wrote:
grauzone wrote:
You're not testing for types, you're testing if it compiles. Inside
the tested block of code, all sorts of things could go wrong. You
can't know if is(typeof(...)) really did what you wanted, or if
something broke.
You're testing, is everything inside that OK?. If you want to know
WHY it's wrong, you'd better make sure you're testing something simple.
Andrei's range lib uses it more in a way does this type support this
and that range interface?. Example:
http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L58
Then different isXxxRange are used by higher-order ranges in defining
refined interfaces depending on the interfaces offered by their inputs.
I fail to see how that's terrible. I am very happy D has that feature -
no other statically-typed language has it, and it can be used to great
effect. Look e.g. at Chain:
http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L799
There, the uses of static if (is(...)) allow Chain to define as capable
an interface as its inputs allow.
Andrei
I really like Andrei's range library, I use it all the time when I need
to pass slices of generic types around, it really is more convenient
than a pair of iterators.
The way I see ranges is as a form of interface without being bound to
classes; its the only way to make structs and D arrays pass the
isXxxRange traits.
The prototypes for using ranges then just go from:
void dosomething(T)(IForwardRange!T range) {}
to
void dosomething(Range)(Range range) if(isForwardRange!Range) {}
and it means the same thing, but you can't send a string to IForwardRange.
Re: Metaprogramming in D : Some Real-world Examples
Bill Baxter wrote: On Mon, Nov 9, 2009 at 6:03 PM, Andrei Alexandrescu seewebsiteforem...@erdani.org wrote: Bill Baxter wrote: On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright newshou...@digitalmars.com wrote: Looks like Bill Baxter is giving a presentation on D Nov. 18! http://www.nwcpp.org/ Yep, that's right, and I'd be quite grateful to you smart folks here if you could share your meta-programming favorites with me! If you've got a real-world example of meta-programming in D that you think is particularly handy, then please send it my way I'm looking for small-but-useful things that are easy to explain, and make something easier than it would be otherwise. Things like places where static if can save your butt, or loop unrolling, and passing code snippets to functions like in std.algorithm. Things like a compile-time raytracer or regexp parser (though quite cool!) are not what I'm after. Too involved for a short talk. --bb std.random has code that checks the parameters of a congruential RNG during compilation. That's also an example in TDPL. This looks good. Any chance you could send me the snippet of the book that explains the rationale for what constitutes proper linear congruential parameters? --bb It's been online for a while. http://erdani.com/tdpl/excerpt.pdf Andrei
Re: Metaprogramming in D : Some Real-world Examples
On Thu, Nov 12, 2009 at 7:53 AM, Andrei Alexandrescu seewebsiteforem...@erdani.org wrote: Bill Baxter wrote: On Mon, Nov 9, 2009 at 6:03 PM, Andrei Alexandrescu seewebsiteforem...@erdani.org wrote: Bill Baxter wrote: On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright newshou...@digitalmars.com wrote: Looks like Bill Baxter is giving a presentation on D Nov. 18! http://www.nwcpp.org/ Yep, that's right, and I'd be quite grateful to you smart folks here if you could share your meta-programming favorites with me! If you've got a real-world example of meta-programming in D that you think is particularly handy, then please send it my way I'm looking for small-but-useful things that are easy to explain, and make something easier than it would be otherwise. Things like places where static if can save your butt, or loop unrolling, and passing code snippets to functions like in std.algorithm. Things like a compile-time raytracer or regexp parser (though quite cool!) are not what I'm after. Too involved for a short talk. --bb std.random has code that checks the parameters of a congruential RNG during compilation. That's also an example in TDPL. This looks good. Any chance you could send me the snippet of the book that explains the rationale for what constitutes proper linear congruential parameters? --bb It's been online for a while. http://erdani.com/tdpl/excerpt.pdf Thanks, I guess I saw that at some point, but forgot what it contained. --bb
Re: Metaprogramming in D : Some Real-world Examples
Bill Baxter wrote: ... This is almost just a preprocessor macro trick, except for this line: mixin( FoldStringsOf!visitMethodOf( [Sum, Product] ) ); The essence is to generate a bunch of methods from a list of names. I was thinking to include a similar example from the world of 3d graphics, which is generating all the swizzles of a vector* (got the idea from Tom S.). That's got the method generation from a list, but it also generates the list too. Interesting. I noticed it's also possible to pass a module as an alias and to things with it, but haven't come across an example of where that would be used. Modules are almost something in D, but just not yet. Another way is to have a swizz member template that lets you do v.swiz(zyx). That's arguably better in that you don't pay for it if you don't use it. But being able to generate all the methods with D is still kinda spiffy. * Most GPU languages (HLSL,glsl,Cg) have a swizzle syntax, such that for a float3 v; v.zyx gives you float3(v.z,v.y,v.x). And this works for all suffixes. v.xxx, v.xzy, etc. Also for different numbers of components. eg. v.xz is float2(v.x,v.z). --bb swizzling is a neat example! I also have code that actually implements the visitor interface with stubs that print, throw or assert, but it's kind of hairy.
Re: Metaprogramming in D : Some Real-world Examples
On Tue, Nov 10, 2009 at 1:27 AM, Bill Baxter wbax...@gmail.com wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
I think tuples are a good example of something that makes your life
easier, lately I've been very fond of this little snippet:
void delegate() Bind(Args...)(void delegate(Args) dg, Args args)
{
struct Closure
{
Args arguments;
void delegate(Args) callee;
void call()
{
callee(arguments);
}
}
auto c = new Closure;
// foreach not strictly necessary, but ldc currently chokes on
just an assignment... I should fix that..
foreach(i,a;args)
c.arguments[i] = a;
c.callee = dg;
return c.call;
}
class C
{
void foo(int,float) {}
}
void main()
{
auto c = new C;
auto dg = Bind(c.foo, 1, 2.0f);
// register delegate somewhere
}
Not sure if this gets easier in C++0x , haven't read up on that...
Nothing fancy, but it sure has made my life easier.
-Tomas
Re: Metaprogramming in D : Some Real-world Examples
Andrei Alexandrescu wrote:
grauzone wrote:
Lars T. Kyllingstad wrote:
Jacob Carlborg wrote:
On 11/10/09 01:27, Bill Baxter wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
This is invaluable to me, which makes it possible to do some form of
duck typing at compile time:
static if (is(typeof({
/* does this compile */
})))
There are forces at work (Don, that is) attempting to get rid of that
very construct and replace it with something better:
http://www.digitalmars.com/d/archives/digitalmars/D/Proposal_Replace_traits_and_is_typeof_XXX_with_a_magic_namespace_._99914.html
In my humble opinion, is(typeof({...})) is an ugly creature. I really
don't think it should be put under a spotlight as a good example of D
metaprogramming. If anything, please use __traits(compiles, {...})
instead.
Who cares about ugly syntax, if the idea is bad in the first place?
I think testing types during compilation isn't bad. Under what
circumstances is it?
You're not testing for types, you're testing if it compiles. Inside the
tested block of code, all sorts of things could go wrong. You can't know
if is(typeof(...)) really did what you wanted, or if something broke. At
least when you're doing more complex stuff with is(typeof), the danger
of silent failures increases. Suppose the user makes an error in his
custom range type by specifying a wrong return type (or whatever), and
the range library just ignores his range-related function. Maybe that
range function was optional, which will end in the range library
seemingly ignoring his function. Can this be good? (I don't know if that
case I described can even happen in your ranges lib, but I think this is
a typical failure that could happen with is(typeof).)
This isn't even compiletime duck typing anymore, it's try-and-error
built into the compiler. Even worse, now having semantically incorrect
code in D sources is perfectly fine for weird reasons, and the compiler
has to swallow some kinds of semantics errors.
Really, wouldn't some mechanism to explicitly check for compile time
contracts better?
For me, this is some sort of metaprogramming WTF. This all makes me
cringe. Sorry about that.
Andrei
Re: Metaprogramming in D : Some Real-world Examples
Christopher Wright wrote: grauzone wrote: You're not testing for types, you're testing if it compiles. Inside the tested block of code, all sorts of things could go wrong. You can't know if is(typeof(...)) really did what you wanted, or if something broke. You're testing, is everything inside that OK?. If you want to know WHY it's wrong, you'd better make sure you're testing something simple. So it requires caution, and you want to keep the contents small. It's useful, but it requires caution. I don't even think it particularly requires caution. If it passes, you know everything is OK. It's just that it's an all-or-nothing test. IMHO, one of the best features of it, is that you can have negative compile-time unit tests. You can create tests which must be rejected at compile time. I don't know of any other clean way to do that.
Re: Metaprogramming in D : Some Real-world Examples
grauzone wrote: Don wrote: Christopher Wright wrote: grauzone wrote: You're not testing for types, you're testing if it compiles. Inside the tested block of code, all sorts of things could go wrong. You can't know if is(typeof(...)) really did what you wanted, or if something broke. You're testing, is everything inside that OK?. If you want to know WHY it's wrong, you'd better make sure you're testing something simple. Andrei's range lib uses it more in a way does this type support this and that range interface?. Example: http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L58 Then different isXxxRange are used by higher-order ranges in defining refined interfaces depending on the interfaces offered by their inputs. I fail to see how that's terrible. I am very happy D has that feature - no other statically-typed language has it, and it can be used to great effect. Look e.g. at Chain: http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L799 There, the uses of static if (is(...)) allow Chain to define as capable an interface as its inputs allow. Andrei
Re: Metaprogramming in D : Some Real-world Examples
Andrei Alexandrescu wrote:
grauzone wrote:
Don wrote:
Christopher Wright wrote:
grauzone wrote:
You're not testing for types, you're testing if it compiles. Inside
the tested block of code, all sorts of things could go wrong. You
can't know if is(typeof(...)) really did what you wanted, or if
something broke.
You're testing, is everything inside that OK?. If you want to know
WHY it's wrong, you'd better make sure you're testing something simple.
Andrei's range lib uses it more in a way does this type support this
and that range interface?. Example:
http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L58
Then different isXxxRange are used by higher-order ranges in defining
refined interfaces depending on the interfaces offered by their inputs.
That means if one isXxxRange fails because the user maybe made a typo in
the needed range function, the code will silently do something else.
But my main problem is that the user just gets a does not match
template declaration compiler error when he messes up his range
interface. He's neither told that e.g. his range-related function
returns the wrong type, nor is there any other refined error message.
Now what if we'd introduce some sort of interfaces for type checking at
compile time?
interface InputRange(T) {
void popFront();
bool empty();
T front();
}
struct MyRange : InputRange!(int) {
void popFront() { ... }
//compiler error goes here...
void empty() { ... }
int front() { ... }
}
(or something like this)
PS: there are two aspects to the problem: 1. even compile time duck
typing shares some of the problems of runtime duck typing, and 2.
utterly unhelpful error messages. If you wouldn't explicitly check the
interface with is(typeof()), the compiler's error messages would be even
worse because of 1.
I fail to see how that's terrible. I am very happy D has that feature -
no other statically-typed language has it, and it can be used to great
effect. Look e.g. at Chain:
http://dsource.org/projects/phobos/browser/trunk/phobos/std/range.d#L799
There, the uses of static if (is(...)) allow Chain to define as capable
an interface as its inputs allow.
Andrei
Re: Metaprogramming in D : Some Real-world Examples
On Tue, 10 Nov 2009 03:27:20 +0300, Bill Baxter wbax...@gmail.com wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
kprintf (a printf variant) in XoMB is a nice example imo. It accepts
format as a template parameter, doing all the checks at compile-time (and
more).
http://github.com/xomboverlord/xomb-bare-bones/blob/6d924a9fd7cafe43aa50f38c0cd04c44187d4993/kernel/core/kprintf.d
/* This template will generate code for printing and will do
* all parsing of the format string at compile time
*
* USAGE:
* kprintf!(format string {specifier} ... )(args...);
*
* EXAMPLES:
* kprintf!(Integer: {})(10);
* kprintf!({!cls}Cleared the screen.)();
* kprintf!({!pos:2,3}At position (2,3))();
* kprintf!({!fg:LightBlue!bg:Gray}{})(25);
* kprintf!({!fg:Red}redness)();
* kprintf!({x} Hex!)(145);
* kprintf!(Curly Brace: {{)();
*
* COMMANDS:
* !cls - Clears the screen.
* !fg - Sets the foreground color, see the Color enum
*in kernel/dev/console.d.
* !bg - Sets the background color, same as above.
* !pos - Moves the cursor to the x and y given, see example above.
*
* SPECIFIERS:
* {x} - Prints the hex value.
* {u} - Treats as unsigned.
* {} - Prints common form.
*
* WHY IS IT COOL?
* - Compile time parsing of format strings
* - Type checking at compile time as well
* - That means it can tell you that you are dumb before you execute.
* - No need to specify type information.
*
* - So we can do this and not care about the
* output of the function:
*
* auto blah = someFunction();
* kprintf!(Some Arbitrary Info: {})(blah);
*
* WOWWY WOW WOW!
*
*/
Re: Metaprogramming in D : Some Real-world Examples
On 11/10/09 01:27, Bill Baxter wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
This is invaluable to me, which makes it possible to do some form of
duck typing at compile time:
static if (is(typeof({
/* does this compile */
})))
Then I have some other things, not the most useful stuff but still usable:
Get the name of a function
Get the parameter names of a function
Get the field names of a class/struct
Get/set private fields of a class/struct outside the module
Call a function with named arguments
Then some templates that check if a type has a (class) method
Re: Metaprogramming in D : Some Real-world Examples
Jacob Carlborg wrote:
On 11/10/09 01:27, Bill Baxter wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
This is invaluable to me, which makes it possible to do some form of
duck typing at compile time:
static if (is(typeof({
/* does this compile */
})))
There are forces at work (Don, that is) attempting to get rid of that
very construct and replace it with something better:
http://www.digitalmars.com/d/archives/digitalmars/D/Proposal_Replace_traits_and_is_typeof_XXX_with_a_magic_namespace_._99914.html
In my humble opinion, is(typeof({...})) is an ugly creature. I really
don't think it should be put under a spotlight as a good example of D
metaprogramming. If anything, please use __traits(compiles, {...}) instead.
-Lars
Re: Metaprogramming in D : Some Real-world Examples
On Tue, Nov 10, 2009 at 4:29 AM, Lars T. Kyllingstad
pub...@kyllingen.nospamnet wrote:
Jacob Carlborg wrote:
On 11/10/09 01:27, Bill Baxter wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
This is invaluable to me, which makes it possible to do some form of duck
typing at compile time:
static if (is(typeof({
/* does this compile */
})))
There are forces at work (Don, that is) attempting to get rid of that very
construct and replace it with something better:
http://www.digitalmars.com/d/archives/digitalmars/D/Proposal_Replace_traits_and_is_typeof_XXX_with_a_magic_namespace_._99914.html
In my humble opinion, is(typeof({...})) is an ugly creature. I really don't
think it should be put under a spotlight as a good example of D
metaprogramming. If anything, please use __traits(compiles, {...}) instead.
I really liked the meta.compiles(...) or meta(compiles, ...) idea.
You're right though. I would rather show things that look
deliberately designed to do the job nicely instead of things that look
like hacks. Unfortunately, a lot of real-world D meta-programming
currently requires hacky-looking things. So I can't really avoid them
all.
--bb
Re: Metaprogramming in D : Some Real-world Examples
grauzone wrote:
Lars T. Kyllingstad wrote:
Jacob Carlborg wrote:
On 11/10/09 01:27, Bill Baxter wrote:
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
This is invaluable to me, which makes it possible to do some form of
duck typing at compile time:
static if (is(typeof({
/* does this compile */
})))
There are forces at work (Don, that is) attempting to get rid of that
very construct and replace it with something better:
http://www.digitalmars.com/d/archives/digitalmars/D/Proposal_Replace_traits_and_is_typeof_XXX_with_a_magic_namespace_._99914.html
In my humble opinion, is(typeof({...})) is an ugly creature. I really
don't think it should be put under a spotlight as a good example of D
metaprogramming. If anything, please use __traits(compiles, {...})
instead.
Who cares about ugly syntax, if the idea is bad in the first place?
I think testing types during compilation isn't bad. Under what
circumstances is it?
Andrei
Re: Metaprogramming in D : Some Real-world Examples
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright newshou...@digitalmars.com wrote: Looks like Bill Baxter is giving a presentation on D Nov. 18! http://www.nwcpp.org/ Yep, that's right, and I'd be quite grateful to you smart folks here if you could share your meta-programming favorites with me! If you've got a real-world example of meta-programming in D that you think is particularly handy, then please send it my way I'm looking for small-but-useful things that are easy to explain, and make something easier than it would be otherwise. Things like places where static if can save your butt, or loop unrolling, and passing code snippets to functions like in std.algorithm. Things like a compile-time raytracer or regexp parser (though quite cool!) are not what I'm after. Too involved for a short talk. --bb
Re: Metaprogramming in D : Some Real-world Examples
Bill Baxter wrote: On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright newshou...@digitalmars.com wrote: Looks like Bill Baxter is giving a presentation on D Nov. 18! http://www.nwcpp.org/ Yep, that's right, and I'd be quite grateful to you smart folks here if you could share your meta-programming favorites with me! If you've got a real-world example of meta-programming in D that you think is particularly handy, then please send it my way I'm looking for small-but-useful things that are easy to explain, and make something easier than it would be otherwise. Things like places where static if can save your butt, or loop unrolling, and passing code snippets to functions like in std.algorithm. Things like a compile-time raytracer or regexp parser (though quite cool!) are not what I'm after. Too involved for a short talk. --bb std.random has code that checks the parameters of a congruential RNG during compilation. That's also an example in TDPL. Andrei
Re: Metaprogramming in D : Some Real-world Examples
Bill Baxter wbax...@gmail.com wrote in message
news:mailman.290.1257812868.20261.digitalmars-d-annou...@puremagic.com...
On Mon, Nov 9, 2009 at 4:09 PM, Walter Bright
newshou...@digitalmars.com wrote:
Looks like Bill Baxter is giving a presentation on D Nov. 18!
http://www.nwcpp.org/
Yep, that's right, and I'd be quite grateful to you smart folks here
if you could share your meta-programming favorites with me! If
you've got a real-world example of meta-programming in D that you
think is particularly handy, then please send it my way
I'm looking for small-but-useful things that are easy to explain, and
make something easier than it would be otherwise. Things like places
where static if can save your butt, or loop unrolling, and passing
code snippets to functions like in std.algorithm.
Things like a compile-time raytracer or regexp parser (though quite
cool!) are not what I'm after. Too involved for a short talk.
--bb
I have a few things, mostly part of my SemiTwist D Tools project
(http://www.dsource.org/projects/semitwist/):
=== Trace / Trace Value ===
Two of my personal favorites (particularly traceVal). Great for debugging.
Implementation and Documentation (search for trace and traceVal,
implementations are less than 10 lines each):
http://www.dsource.org/projects/semitwist/browser/trunk/src/semitwist/util/mixins.d
Quick Example:
-
mixin(trace!());
mixin(trace!(--EASY TO VISUALLY GREP--));
int myVar=100;
mixin(traceVal!(myVar ));
mixin(traceVal!(myVar-1));
mixin(traceVal!(min(4,7), max(4,7)));
-
Output:
-
C:\path\file.d(1): trace
--EASY TO VISUALLY GREP--: C:\path\file.d(3): trace
myVar : 100
myVar-1: 99
min(4,7): 4
max(4,7): 7
-
There's also a traceMixin that can be useful for debugging mixins (it'll
replace a normal string mixin and echo at compile time via pragma(msg, )
the string being mixed in).
=== Init Member ===
Great for DRY in constructors with many initialization parameters.
Implementation and Documentation (at the top of the file):
http://www.dsource.org/projects/semitwist/browser/trunk/src/semitwist/util/mixins.d
Quick Example:
-
mixin(initMember!(someVar));
mixin(initMember!(a, b, c));
-
Turns Into:
-
this.someVar = someVar;
this.a = a;
this.b = b;
this.c = c;
-
Some variations are also available, such as initMemberFrom for copy
constructors and initFrom copying class members to local vars.
=== Getters ===
DRY mixins for publicly read-only properties, and a lazy version for
lazily computed cached read-only properties. A poor replacement for a real
DRY property syntax, but the next best thing.
Implementation and Documentation (search for getter and getterLazy):
http://www.dsource.org/projects/semitwist/browser/trunk/src/semitwist/util/mixins.d
Quick Example:
-
// Third param optional
mixin(getter!(float, someFloat, 2.5));
mixin(getterLazy!(int, myVar));
private int _myVar_gen()
{
// Ordinarily, this function would be much more complex
// Also, any member func can set _myVar_cached = false;
// to force this to be re-computed on the next request.
return 7;
}
-
Turns Into:
-
private float _someFloat = 2.5;
private float someFloat(float _NEW_VAL_)
{
_someFloat = _NEW_VAL_;
return _someFloat;
}
public float someFloat()
{
return _someFloat;
}
private int _myVar;
private bool _myVar_cached = false;
public int myVar() {
if(!_myVar_cached) {
_myVar_cached = true;
_myVar = _myVar_gen();
}
return _myVar;
}
private int _myVar_gen()
{
// Ordinarily, this function would be much more complex
// Also, any member func can set _myVar_cached = false;
// to force this to be re-computed on the next request.
return 7;
}
-
Variations are also available to use protected (or anything else) instead
of private.
=== Defer Assert/Ensure ===
Uses metaprogramming to create an alternative to assert() that provides much
of the usefulness of JUnit-style libs, but without the bulk of wrapping
things like '==' and '||' in classes/structs or forcing unnatural syntax
like '(a.equals(b)).or(c.notEquals(d))'. Also reports unexpected exceptions
and allows requiring a particular exception to be thrown. Implemented in
less than 200 lines, including blank lines and comments.
Implementation:
http://www.dsource.org/projects/semitwist/browser/trunk/src/semitwist/util/deferAssert.d
Simple Test App:
http://www.dsource.org/projects/semitwist/browser/trunk/src/semitwist/apps/tests/deferAssertTest/main.d
Quick Example:
-
int foo = 2;
mixin(deferAssert!(`foo == 3 || foo 5`, foo is bad));
mixin(deferEnsure!(`foo`, `_ == 3 || _ 5`, ensure foo
