I want to build a linked list of data in yacc.
My Grammar reads like this:
list: item
| list ',' item
;
I have put the appropriate structures in place in the declarations section. But I am not able to figure out a way to get a linked list out of this data. I have to store the recursively obtained data and then redirect it for other purposes.
Basically I am looking for a solution like this one:
https://stackoverflow.com/a/1429820/5134525
But this solution is for right recursion and doesn't work with left.
It depends heavily on how you implement your linked list, but once you have that, it is straight-forward. Something like:
struct list_node {
struct list_node *next;
value_t value;
};
struct list {
struct list_node *head, **tail;
};
struct list *new_list() {
struct list *rv = malloc(sizeof(struct list));
rv->head = 0;
rv->tail = &rv->head;
return rv; }
void push_back(struct list *list, value_t value) {
struct list_node *node = malloc(sizeof(struct list_node));
node->next = 0;
node->value = value;
*list->tail = node;
list->tail = &node->next; }
allows you to write your yacc code as:
list: item { push_back($$ = new_list(), $1); }
| list ',' item { push_back($$ = $1, $3); }
;
of course, you should probably add checks for running out of memory, and exit gracefully in that case.
If you use a left recursive rule, then you need to push the new item at the end of the list rather than the beginning.
If your linked list implementation doesn't support push_back, then push the successive items at the front and reverse the list when its finished.
Very simple.
list
: item
{
$$ = new MyList<SomeType>();
$$.add($1);
}
| list ',' item
{
$1.add($3);
$$ = $1;
}
;
assuming you are using C++, which you didn't state, and assuming you have some MyList<T> class with an add(T) method.
Related
Can I iterate through only a part of a list in e, in a constraint.
For example, this code will go through the whole layer_l list:
<'
struct layer_s {
a : int;
keep soft a == 3;
};
struct layer_gen_s {
n_layers : int;
keep soft n_layers == 8;
layer_l : list of layer_s;
keep layer_l.size() == read_only(n_layers);
};
extend sys {
layer_gen : layer_gen_s;
run() is also {
messagef(LOW, "n_layers = %0d", layer_gen.n_layers);
for each in layer_gen.layer_l{
messagef(LOW, "layer[%2d]: a = %0d", index, it.a);
};
};
};
-- this will go through all layer_l
extend layer_gen_s {
keep for each (layer) using index (i) in layer_l {
layer.a == 7;
};
};
But, I would like to only iterate the for each in through, for example, 2 items. I tried the code below, but it doesn't work:
-- this produces an error
extend layer_gen_s {
keep for each (layer) using index (i) in [layer_l.all(index < 2)] {
layer.a == 7;
};
};
Also I don't want to use implication, so this is not what I want:
-- not what I want, I want to specify directly in iterated list
extend layer_gen_s {
keep for each (layer) using index (i) in layer_l {
(i < 2) => {
layer.a == 7;
};
};
};
Using the list slicing operator doesn't work either, because the path in a for..each constraint is limited to a simple path (e.g. a list variable). The following doesn't work either:
keep for each (layer) using index (i) in layer_l[0..2] {
//...
};
This is a Specman limitation.
To force looping over a sub-list your only bet is to create that sub-list as a separate variable:
layer_subl: list of layer_s;
keep layer_subl.size() == 3;
keep for each (layer) using index (i) in layer_subl {
layer == layer_l[i];
};
Now you can loop on only the first 3 elements within your for..each constraint:
keep for each (layer) in layer_subl {
layer.a == 7;
};
This avoids using implication inside the constraint. Whether this is worth is for you to decide. Also note that the lists will contain the same objects (this is good). No extra struct objects get created.
Creation of the sub-list like this is boilerplate code that could be handled by the tool itself. This would make the code much more concise and readable. You could contact your vendor and request this feature.
The Perl 6 docs list a bunch of types. Some of them, such as Str, have more complicated box/unbox behaviors.
Is it possible to define my own type, specifying my own routines for the box/unboxing? For a particular project, I have a bunch of types I'm reusing, and basically cut/pasting my accessor functions over and over.
For example, the C Struct uses a time_t, and I plug in accessor methods to go to/from a DateTime. Another example is a comma-separated list, I'd like to go to/from an Array and take care of the split/join automagically.
Is there a better way to do this?
Edit: Add Example:
constant time_t = uint64;
constant FooType_t = uint16;
enum FooType <A B C>;
class Foo is repr('CStruct') is rw
{
has uint32 $.id;
has Str $.name;
has FooType_t $.type;
has time_t $.time;
method name(Str $n?) {
$!name := $n with $n;
$!name;
}
method type(FooType $t?) {
$!type = $t with $t;
FooType($!type);
}
method time(DateTime $d?) {
$!time = .Instant.to-posix[0].Int with $d;
DateTime.new($!time)
}
}
my $f = Foo.new;
$f.id = 12;
$f.name('myname');
$f.type(B);
$f.time(DateTime.new('2000-01-01T12:34:56Z'));
say "$f.id() $f.name() $f.type() $f.time()";
# 12 myname B 2000-01-01T12:34:56Z
This works, I can set the various fields of the CStruct in Perl-ish ways (no lvalue, but I can pass them in as parameters).
Now I want to use time_t, FooType_t, etc. for many fields in a lot of structs and have them act the same way. Is there a better way other than to just copy those methods over and over?
Maybe macros could help here? I haven't mastered them yet.
You could write a trait that handles automatic attribute conversion on fetching or storing the attribute. The following should get you started:
multi sub trait_mod:<is>(Attribute:D $attr, :$autoconv!) {
use nqp;
my $name := $attr.name;
$attr.package.^add_method: $name.substr(2), do given $attr.type {
when .REPR eq 'P6int' {
method () is rw {
my $self := self;
Proxy.new:
FETCH => method () {
$autoconv.out(nqp::getattr_i($self, $self.WHAT, $name));
},
STORE => method ($_) {
nqp::bindattr_i($self, $self.WHAT, $name,
nqp::decont($autoconv.in($_)));
}
}
}
default {
die "FIXME: no idea how to handle {.^name}";
}
}
}
For example, take your use case of time_t:
constant time_t = uint64;
class CTimeConversion {
multi method in(Int $_ --> time_t) { $_ }
multi method in(DateTime $_ --> time_t) { .posix }
method out(time_t $_ --> DateTime) { DateTime.new($_) }
}
class CTimeSpan is repr<CStruct> {
has time_t $.start is autoconv(CTimeConversion);
has time_t $.end is autoconv(CTimeConversion);
}
Finally, some example code to show it works:
my $span = CTimeSpan.new;
say $span;
say $span.end;
$span.end = DateTime.now;
say $span;
say $span.end;
How does one write custom accessor methods in Perl6?
If I have this class:
class Wizard {
has Int $.mana is rw;
}
I can do this:
my Wizard $gandalf .= new;
$gandalf.mana = 150;
Let's say I want to add a little check to a setter in my Perl6 class without giving up the $gandalf.mana = 150; notation (in other words, I don't want to write this: $gandalf.setMana(150);). The program should die, if it tries to set a negative mana. How do I do this? The Perl6 documentation just mentions it is possible to write custom accessors, but does not say how.
With more recent versions of Rakudo there is a subset named UInt that restricts it to positive values.
class Wizard {
has UInt $.mana is rw;
}
So that you're not stuck in a lurch if you need to something like this; here is how that is defined:
( you can leave off the my, but I wanted to show you the actual line from the Rakudo source )
my subset UInt of Int where * >= 0;
You could also do this:
class Wizard {
has Int $.mana is rw where * >= 0;
}
I would like to point out that the * >= 0 in the where constraint is just a short way to create a Callable.
You could have any of the following as a where constraint:
... where &subroutine # a subroutine that returns a true value for positive values
... where { $_ >= 0 }
... where -> $a { $a >= 0 }
... where { $^a >= 0 }
... where $_ >= 0 # statements also work ( ｢$_｣ is set to the value it's testing )
( If you wanted it to just not be zero you could also use ... where &prefix:<?> which is probably better spelled as ... where ?* or ... where * !== 0 )
If you feel like being annoying to people using your code you could also do this.
class Wizard {
has UInt $.mana is rw where Bool.pick; # accepts changes randomly
}
If you want to make sure the value "makes sense" when looking at all of the values in the class in aggregate, you will have to go to a lot more work.
( It may require a lot more knowledge of the implementation as well )
class Wizard {
has Int $.mana; # use . instead of ! for better `.perl` representation
# overwrite the method the attribute declaration added
method mana () is rw {
Proxy.new(
FETCH => -> $ { $!mana },
STORE => -> $, Int $new {
die 'invalid mana' unless $new >= 0; # placeholder for a better error
$!mana = $new
}
)
}
}
You can get the same accessor interface that saying $.mana provides by declaring a method is rw. Then you can wrap a proxy around the underlying attribute like so:
#!/usr/bin/env perl6
use v6;
use Test;
plan 2;
class Wizard {
has Int $!mana;
method mana() is rw {
return Proxy.new:
FETCH => sub ($) { return $!mana },
STORE => sub ($, $mana) {
die "It's over 9000!" if ($mana // 0) > 9000;
$!mana = $mana;
}
}
}
my Wizard $gandalf .= new;
$gandalf.mana = 150;
ok $gandalf.mana == 150, 'Updating mana works';
throws_like sub {
$gandalf.mana = 9001;
}, X::AdHoc, 'Too much mana is too much';
Proxy is basically a way to intercept read and write calls to storage and do something other than the default behavior. As their capitalization suggests, FETCH and STORE are called automatically by Perl to resolve expressions like $gandalf.mana = $gandalf.mana + 5.
There's a fuller discussion, including whether you should even attempt this, at PerlMonks. I would recommend against the above -- and public rw attributes in general. It's more a display of what it is possible to express in the language than a useful tool.
I am using libclang to parse a objective c source code file. The following code finds all Objective-C instance method declarations, but it also finds declarations in the includes:
enum CXCursorKind curKind = clang_getCursorKind(cursor);
CXString curKindName = clang_getCursorKindSpelling(curKind);
const char *funcDecl="ObjCInstanceMethodDecl";
if(strcmp(clang_getCString(curKindName),funcDecl)==0{
}
How can I skip everything, which comes from header includes? I am only interested in my own Objective-C instance method declarations in the source file, not in any of the includes.
e.g. the following should not be included
...
Location: /System/Library/Frameworks/Foundation.framework/Headers/NSObject.h:15:9:315
Type:
TypeKind: Invalid
CursorKind: ObjCInstanceMethodDecl
...
Answering this question because I couldn't believe that hard-coding paths comparisons was the only solution, and indeed, there is a clang_Location_isFromMainFile function that does exactly what you want, so that you can filter unwanted results in the visitor, like this :
if (clang_Location_isFromMainFile (clang_getCursorLocation (cursor)) == 0) {
return CXChildVisit_Continue;
}
The only way I know would be to skip unwanted paths during the AST visit. You can for example put something like the following in your visitor function. Returning CXChildVisit_Continue avoids visiting the entire file.
CXFile file;
unsigned int line, column, offset;
CXString fileName;
char * canonicalPath = NULL;
clang_getExpansionLocation (clang_getCursorLocation (cursor),
&file, &line, &column, &offset);
fileName = clang_getFileName (file);
if (clang_getCString (fileName)) {
canonicalPath = realpath (clang_getCString (fileName), NULL);
}
clang_disposeString (fileName);
if (strcmp(canonicalPath, "/canonical/path/to/your/source/file") != 0) {
return CXChildVisit_Continue;
}
Also, why compare CursorKindSpelling instead of the CursorKind directly?
Is there any way to serialize a dictionary using protocol buffers, or I'll have to use Thrift if I need that?
For future answer seekers, ProtoBuf now supports Maps natively:
message MapMessage
{
map<string, string> MyMap = 1;
}
Protobuf specification now supports dictionaries (maps) natively.
Original answer
People typically write down the dictionary as a list of key-value pairs, and then rebuild the dictionary on the other end.
message Pair {
string key = 1;
string value = 2;
}
message Dictionary {
repeated Pair pairs = 1;
}
You can check the ProtoText package.
Assume you want to serialize a dict person_dict to a pre-defined PersonBuf protobuf object defined in personbuf_pb2 module.
In this case, to use ProtoText,
import ProtoText
from personbuf_pb2 import PersonBuf
obj = PersonBuf()
obj.update(person_dict)
I firstly comment the #Flassari 's answer as it is really convenient.
However, in my case, I needed map<Type, repeated AnyModel> where :
enum Type {
Undefined = 0;
Square = 1;
Circle = 2;
}
message AnyModel {
string Name = 1;
}
Here I just want to return a dictionary that, for each type, contain a list of AnyModel
However, I didn't find a better workaround than the one proposed by #JesperE so I did the following: (as you can't use enum as key in map)
message MyRPCBodyCall {
map<string, AnyModels> Models = 1;
}
enum Type {
Undefined = 0;
Square = 1;
Circle = 2;
}
message AnyModel {
string Name = 1;
}
message AnyModelArray {
repeated AnyModel AnyModels = 1;
}
Here I convert from/to string my enum using my chosen code languages from both server/client side
So both approaches are actually valid answers IMO, depends on your requirements.