I have something that I can do easily in Perl, but not in Raku without fiddling around with flag variables. Here's the Perl code:
#!/usr/bin/perl
MAIN_BLOCK: {
foreach $item (1 2 3 4 5) {
$item == 6 and last MAIN_BLOCK;
}
print "No items matched!\n";
}
The relevant difference here is that Perl will allow you to use last to exit from any labelled block. Raku will only do this if the block is a loop.
Is there a good way to do this? I feel like there should be a phaser for this, but haven't figured out how to do it without flag variables, which seem like they should be avoidable.
Thanks,
Raku supports similar control flow with given blocks.
Here's a fairly literal translation (i.e., not necessarily idiomatic Raku) from the Perl code you posted:
given * {
for ^6 -> $item {
succeed if $item == 6;
}
default { print "No items matched!\n"; }
}
edit: Oh, and for a less-literally-translated/more-idiomatic-Raku solution, well, TIMTOWTDI but I might go with returning from an anonymous sub:
sub { for ^6 { return when 6 }
say "No items matched!" }()
(Of course, I suppose it's possible that the most Raku-ish way to solve do that doesn't involve any Raku syntax at all – but instead involves modifying one of Raku's braided languages to allow for loops to take an else block. But I'm not advising those sort of shenanigans!)
I know that this will not work, since I tried it:
if $r ~~ BearingTrue || CompassAdj || CourseAdj { nextsame };
But - is there a neat, concise and legible way to do multiple Type smart matches on one line rather than have to expand to a given/when or if/else construct?
Have you tried :
if $r ~~ BearingTrue | CompassAdj | CourseAdj { nextsame };
This should give you an Any Junction that with then match OK.
This Answer is to let me address the comment from #jubilatious1 a bit more clearly.
I am working on a new raku module, see line 225 ish here Physics::Navigation
For illustrative purposes, the code now looks like this...
class BearingTrue { ...}
class BearingMag { ...}
sub err-msg { die "Can't mix BearingTrue and BearingMag for add/subtract!" }
class BearingTrue is Bearing is export {
multi method compass { <T> } #get compass
multi method compass( Str $_ ) { #set compass
die "BearingTrue compass must be <T>" unless $_ eq <T> }
method M { #coerce to BearingMag
my $nv = $.value + ( +$variation + +$deviation );
BearingMag.new( value => $nv, compass => <M> )
}
#| can't mix unless BearingMag
multi method add( BearingMag ) { err-msg }
multi method subtract( BearingMag ) { err-msg }
}
So I decided to recast the code to use multi-method add and subtract to check type matches to prevent a lost mariner from adding a magnetic bearing to a true one. I feel that this is cleaner even than Scimon's great answer, since in that instance, my method was accepting all child types of Bearing and then using an if statement to detect a type error.
You are welcome to go...
zef install https://github.com/p6steve/raku-Physics-Navigation.git
then follow the example at the top of bin/synopsis-navigation.raku to use the module and make the various classes available in your own code.
If you are just keen to see how the pieces fit then I suggest writing your own simple classes on similar lines and working through the examples in books such as ThinkRaku chapter 12. I recommend this for the clarity and level of information and it treats inheritance and roles equally.
I am confident that others will feel my code style is over-reliant on inheritance. I feel that since a magnetic-bearing is strictly a derived concept from a bearing-in-general that this is right for my code - but roles and composition is less restrictive and provides similar encapsulation with better maintainability.
In theory, and according to the documentation, you can use any argument for methods in grammar actions.
grammar G {
token TOP { \w+ }
}
class Action-Arg {
method TOP ($match) { $match.make: ~$match }
}
class Action {
method TOP ($/) { make ~$/ }
}
class Action-Fails {
method TOP ($match) { make ~$match }
}
say G.parse( "zipi", actions => Action-Arg );
say G.parse( "zape", actions => Action );
say G.parse( "pantuflo", actions => Action-Fails );
However, the two first versions work as expected. But the third one (which would be a direct translation of the second), fails with
Cannot bind attributes in a Nil type object
in method TOP at match-and-match.p6 line 19
in regex TOP at match-and-match.p6 line 7
in block <unit> at match-and-match.p6 line 24
There's probably some special syntax going on (in the sense of make being actually $/.make, probably), but I'd just like to clarify if this is according to spec or is a bug.
That is because the make subroutine is one of those rare cases in Rakudo where it actually tries to access the $/ variable from the scope it is called from. Which is also how it is documented:
The sub form operates on the current $/
(from the documentation)
I was curious about grammars being classes or singletons, so I created this small program to find out:
grammar Mini {
token TOP { \* <word> \* }
token word { \w+ }
}
proto sub is-class( | ) { * };
multi sub is-class( Grammar:D $g ) { return "Object" };
multi sub is-class( Grammar:U $g ) { return "Class" };
say is-class( Mini );
This uses multiple dispatch to find that out, and it turns out that Mini is actually a class. In general, would there be a shorter way of finding this out? Or a way that would not require to know the actual class of which the package might be an instance?
You can disambiguate 'instances' and 'classes' via DEFINITE, ie
Mini.DEFINITE ?? 'Object' !! 'Class'
or rather
Mini.DEFINITE ?? 'concrete object' !! 'type object'
should do the trick.
I have two modules in separate files within the same crate, where the crate has macro_rules enabled. I want to use the macros defined in one module in another module.
// macros.rs
#[macro_export] // or not? is ineffectual for this, afaik
macro_rules! my_macro(...)
// something.rs
use macros;
// use macros::my_macro; <-- unresolved import (for obvious reasons)
my_macro!() // <-- how?
I currently hit the compiler error "macro undefined: 'my_macro'"... which makes sense; the macro system runs before the module system. How do I work around that?
Macros within the same crate
New method (since Rust 1.32, 2019-01-17)
foo::bar!(); // works
mod foo {
macro_rules! bar {
() => ()
}
pub(crate) use bar; // <-- the trick
}
foo::bar!(); // works
With the pub use, the macro can be used and imported like any other item. And unlike the older method, this does not rely on source code order, so you can use the macro before (source code order) it has been defined.
Old method
bar!(); // Does not work! Relies on source code order!
#[macro_use]
mod foo {
macro_rules! bar {
() => ()
}
}
bar!(); // works
If you want to use the macro in the same crate, the module your macro is defined in needs the attribute #[macro_use]. Note that macros can only be used after they have been defined!
Macros across crates
Crate util
#[macro_export]
macro_rules! foo {
() => ()
}
Crate user
use util::foo;
foo!();
Note that with this method, macros always live at the top-level of a crate! So even if foo would be inside a mod bar {}, the user crate would still have to write use util::foo; and not use util::bar::foo;. By using pub use, you can export a macro from a module of your crate (in addition to it being exported at the root).
Before Rust 2018, you had to import macro from other crates by adding the attribute #[macro_use] to the extern crate util; statement. That would import all macros from util. This syntax should not be necessary anymore.
Alternative approach as of 1.32.0 (2018 edition)
Note that while the instructions from #lukas-kalbertodt are still up to date and work well, the idea of having to remember special namespacing rules for macros can be annoying for some people.
EDIT: it turns out their answer has been updated to include my suggestion, with no credit mention whatsoever 😕
On the 2018 edition and onwards, since the version 1.32.0 of Rust, there is another approach which works as well, and which has the benefit, imho, of making it easier to teach (e.g., it renders #[macro_use] obsolete). The key idea is the following:
A re-exported macro behaves as any other item (function, type, constant, etc.): it is namespaced within the module where the re-export occurs.
It can then be referred to with a fully qualified path.
It can also be locally used / brought into scope so as to refer to it in an unqualified fashion.
Example
macro_rules! macro_name { ... }
pub(crate) use macro_name; // Now classic paths Just Work™
And that's it. Quite simple, huh?
Feel free to keep reading, but only if you are not scared of information overload ;) I'll try to detail why, how and when exactly does this work.
More detailed explanation
In order to re-export (pub(...) use ...) a macro, we need to refer to it! That's where the rules from the original answer are useful: a macro can always be named within the very module where the macro definition occurs, but only after that definition.
macro_rules! my_macro { ... }
my_macro!(...); // OK
// Not OK
my_macro!(...); /* Error, no `my_macro` in scope! */
macro_rules! my_macro { ... }
Based on that, we can re-export a macro after the definition; the re-exported name, then, in and of itself, is location agnostic, as all the other global items in Rust 🙂
In the same fashion that we can do:
struct Foo {}
fn main() {
let _: Foo;
}
We can also do:
fn main() {
let _: A;
}
struct Foo {}
use Foo as A;
The same applies to other items, such as functions, but also to macros!
fn main() {
a!();
}
macro_rules! foo { ... } // foo is only nameable *from now on*
use foo as a; // but `a` is now visible all around the module scope!
And it turns out that we can write use foo as foo;, or the common use foo; shorthand, and it still works.
The only question remaining is: pub(crate) or pub?
For #[macro_export]-ed macros, you can use whatever privacy you want; usually pub.
For the other macro_rules! macros, you cannot go above pub(crate).
Detailed examples
For a non-#[macro_export]ed macro
mod foo {
use super::example::my_macro;
my_macro!(...); // OK
}
mod example {
macro_rules! my_macro { ... }
pub(crate) use my_macro;
}
example::my_macro!(...); // OK
For a #[macro_export]-ed macro
Applying #[macro_export] on a macro definition makes it visible after the very module where it is defined (so as to be consistent with the behavior of non-#[macro_export]ed macros), but it also puts the macro at the root of the crate (where the macro is defined), in an absolute path fashion.
This means that a pub use macro_name; right after the macro definition, or a pub use crate::macro_name; in any module of that crate will work.
Note: in order for the re-export not to collide with the "exported at the root of the crate" mechanic, it cannot be done at the root of the crate itself.
pub mod example {
#[macro_export] // macro nameable at `crate::my_macro`
macro_rules! my_macro { ... }
pub use my_macro; // macro nameable at `crate::example::my_macro`
}
pub mod foo {
pub use crate::my_macro; // macro nameable at `crate::foo::my_macro`
}
When using the pub / pub(crate) use macro_name;, be aware that given how namespaces work in Rust, you may also be re-exporting constants / functions or types / modules. This also causes problems with globally available macros such as #[test], #[allow(...)], #[warn(...)], etc.
In order to solve these issues, remember you can rename an item when re-exporting it:
macro_rules! __test__ { ... }
pub(crate) use __test__ as test; // OK
macro_rules! __warn__ { ... }
pub(crate) use __warn__ as warn; // OK
Also, some false positive lints may fire:
from the trigger-happy clippy tool, when this trick is done in any fashion;
from rustc itself, when this is done on a macro_rules! definition that happens inside a function's body: https://github.com/rust-lang/rust/issues/78894
This answer is outdated as of Rust 1.1.0-stable.
You need to add #![macro_escape] at the top of macros.rs and include it using mod macros; as mentioned in the Macros Guide.
$ cat macros.rs
#![macro_escape]
#[macro_export]
macro_rules! my_macro {
() => { println!("hi"); }
}
$ cat something.rs
#![feature(macro_rules)]
mod macros;
fn main() {
my_macro!();
}
$ rustc something.rs
$ ./something
hi
For future reference,
$ rustc -v
rustc 0.13.0-dev (2790505c1 2014-11-03 14:17:26 +0000)
Adding #![macro_use] to the top of your file containing macros will cause all macros to be pulled into main.rs.
For example, let's assume this file is called node.rs:
#![macro_use]
macro_rules! test {
() => { println!("Nuts"); }
}
macro_rules! best {
() => { println!("Run"); }
}
pub fn fun_times() {
println!("Is it really?");
}
Your main.rs would look sometime like the following:
mod node; //We're using node.rs
mod toad; //Also using toad.rs
fn main() {
test!();
best!();
toad::a_thing();
}
Finally let's say you have a file called toad.rs that also requires these macros:
use node; //Notice this is 'use' not 'mod'
pub fn a_thing() {
test!();
node::fun_times();
}
Notice that once files are pulled into main.rs with mod, the rest of your files have access to them through the use keyword.
I have came across the same problem in Rust 1.44.1, and this solution works for later versions (known working for Rust 1.7).
Say you have a new project as:
src/
main.rs
memory.rs
chunk.rs
In main.rs, you need to annotate that you are importing macros from the source, otherwise, it will not do for you.
#[macro_use]
mod memory;
mod chunk;
fn main() {
println!("Hello, world!");
}
So in memory.rs you can define the macros, and you don't need annotations:
macro_rules! grow_capacity {
( $x:expr ) => {
{
if $x < 8 { 8 } else { $x * 2 }
}
};
}
Finally you can use it in chunk.rs, and you don't need to include the macro here, because it's done in main.rs:
grow_capacity!(8);
The upvoted answer caused confusion for me, with this doc by example, it would be helpful too.
Note: This solution does work, but do note as #ineiti highlighted in the comments, the order u declare the mods in the main.rs/lib.rs matters, all mods declared after the macros mod declaration try to invoke the macro will fail.