I have a matcher that works perfectly for matching operator() calls on instances of a class or classes derived from that class. For example, it matches the final line of:
class MyBase { void operator()(...) {} };
MyBase b;
b(parameters);
using a matcher like:
const auto MyBaseExpr =
expr(hasType(cxxRecordDecl(isSameOrDerivedFrom("::MyBase"))));
Finder->addMatcher(traverse(
TK_AsIs, cxxOperatorCallExpr(
hasOverloadedOperatorName("()"),
hasArgument(0, anyOf(MyBaseExpr, MyOtherBaseExpr)),
hasAnyArgument(...),
this);
But I'd also like to be able to match such calls on instances of typedefs for the base or derived types like in the last line below:
typedef MyBase MyTypedef;
MyTypedef t;
t(parameters);
and I can't seem to fathom the correct way to specify this match. Attempting to use hasUnqualifiedDesugaredType rather than hasType doesn't work since it works on a type rather than a Decl and if I try to do more matching with the type then I can't use isSameOrDerived which returns a Matcher<CXXRecordDecl>. A similar problem occurs when trying to use hasCanonicalType:
.../RedundantStringCStrCheck.cpp:193:40: error: invalid initialization of reference of type ‘const clang::ast_matchers:
:internal::Matcher<clang::QualType>&’ from expression of type ‘clang::ast_matchers::internal::BindableMatcher<clang::Decl>’
193 | expr(hasCanonicalType(cxxRecordDecl(isSameOrDerivedFrom("::MyBase"))));
MyTypedef is defined from MyBase so its Canonical Type should be MyBase. More information about canonical type: https://clang.llvm.org/docs/InternalsManual.html#canonical-types
This is the example from LibASTMatchersReference , it uses hasType().
Thien Tran provided the pointer which led me to the right answer. Here's my original expression
const auto MyBaseExpr =
expr(hasType(cxxRecordDecl(isSameOrDerivedFrom("::MyBase"))));
I was trying to use:
const auto MyBaseExpr =
expr(hasCanonicalType(cxxRecordDecl(isSameOrDerivedFrom("::MyBase"))));
but the description of hasCanonicalType in LibASTMatchersReference shows that it takes and returns Matcher<QualType> yet cxxRecordDecl has type Matcher<Decl>, so this did not compile.
The mismatch of types can be corrected by inserting a call to hasDeclaration. It's then also necessary to keep the call to hasType in order to turn the Matcher<QualType> result of hasCanonicalType back into something that can be passed to expr.
After all that I ended up with:
const auto MyBaseExpr =
expr(hasType(hasCanonicalType(hasDeclaration(cxxRecordDecl(isSameOrDerivedFrom("::MyBase"))))));
which seems to work perfectly.
As per Language specs (10.1.1 Operators) I am trying to override some operators.
I get an analyzer error when overriding the 'minus' and 'unary minus' operators - one that I don't get:
'The operator "-" is not defined on class Indentation'
but in the class I have defined it:
Indentation operator -() {
level--;
return this;
}
and I use it like myInstance--; and it actually does work, but still the analyzer complains and I cannot submit the code 'clean' because of the error.
I have looked up an old thread (Why does overriding negate cause static warning in Dart) but I think it is not relevant here.
Any advise is welcome.
--x is the same as x -= 1. To use it you have to define the operator -(p) (not operator -())
Indentation operator -(n) => new Indentation(level - n);
I'm trying to write a function that does type casting, which seems to be a frequently occurring activity in Rascal code. But I can't seem to get it right. The following and several variations on it fail.
public &T cast(type[&T] tp, value v) throws str {
if (tp tv := v)
return tv;
else
throw "cast failed";
}
Can someone help me out?
Some more info: I frequently use pattern matching against a pattern of the form "Type Var" (i.e. against a variable declaration) in order to tell Rascal that an expression has a certain type, e.g.
map[str,value] m := myexp
This is usually in cases where I know that myexp has type map[str,value], but omitting the matching would make Rascal's type checking mechanism complain.
In order to be a bit more defensive against mistakes, I usually wrap the matching construct in an if-then-else where an exception is raised if the match fails:
if (map[str,value] m := myexp) {
// use m
} else {
throw "cast failed";
}
I would like to shorten all such similar pieces of code using a single function that does the job generically, so that I can write instead
cast(#map[str,value], myexp)
PS. Also see How to cast a value type to Map in Rascal?
It seems that the best way to write this, if you truly need to do this, is the following:
public map[str,value] cast(map[str,value] v) = v;
public default map[str,value] cast(value v) { throw "cast failed!"; }
Then you could just say
m = cast(myexp);
and it would do what you want to do -- the actual pattern matching is moved into the function signature for cast, with a case specific to the type you are wanting to use and a case that handles everything that doesn't otherwise match.
However, I'm still not sure why you are using type value, either here (inside the map) or in the linked question. The "standard" Rascal way of handling cases where you could have one of multiple choices is to define these with a user-defined data type and constructors. You could then use pattern matching to match the constructors, or use the is and has keywords to interrogate a value to check to see if it was created using a specific constructor or if it has a specific field, respectively. The rule for fields is that all occurrences of a field in the constructor definitions for a given ADT have the same type. So, it may help to know more about your usage scenario to see if this definition of cast is the best option or if there is a better solution to your problem.
EDITED
If you are reading JSON, an alternate way to do it is to use the JSON grammar and AST that also live in that part of the library (I think the one you are using is more of a stream reader, like our current text readers and writers, but I would need to look at the code more to be sure). You can then do something like this (long output included to give an idea of the results):
rascal>import lang::json::\syntax::JSON;
ok
rascal>import lang::json::ast::JSON;
ok
rascal>import lang::json::ast::Implode;
ok
ascal>js = buildAST(parse(#JSONText, |project://rascal/src/org/rascalmpl/library/lang/json/examples/twitter01.json|));
Value: object((
"since_id":integer(0),
"refresh_url":string("?since_id=202744362520678400&q=amsterdam&lang=en"),
"page":integer(1),
"since_id_str":string("0"),
"completed_in":float(0.058),
"results_per_page":integer(25),
"next_page":string("?page=2&max_id=202744362520678400&q=amsterdam&lang=en&rpp=25"),
"max_id_str":string("202744362520678400"),
"query":string("amsterdam"),
"max_id":integer(202744362520678400),
"results":array([
object((
"from_user":string("adekamel"),
"profile_image_url_https":string("https:\\/\\/si0.twimg.com\\/profile_images\\/2206104506\\/339515338_normal.jpg"),
"in_reply_to_status_id_str":string("202730522013728768"),
"to_user_id":integer(215350297),
"from_user_id_str":string("366868475"),
"geo":null(),
"in_reply_to_status_id":integer(202730522013728768),
"profile_image_url":string("http:\\/\\/a0.twimg.com\\/profile_images\\/2206104506\\/339515338_normal.jpg"),
"to_user_id_str":string("215350297"),
"from_user_name":string("nurul amalya \\u1d54\\u1d25\\u1d54"),
"created_at":string("Wed, 16 May 2012 12:56:37 +0000"),
"id_str":string("202744362520678400"),
"text":string("#Donnalita122 #NaishahS #fatihahmS #oishiihotchoc #yummy_DDG #zaimar93 #syedames I\'m here at Amsterdam :O"),
"to_user":string("Donnalita122"),
"metadata":object(("result_type":string("recent"))),
"iso_language_code":string("en"),
"from_user_id":integer(366868475),
"source":string("<a href="http:\\/\\/blackberry.com\\/twitter" rel="nofollow">Twitter for BlackBerry\\u00ae<\\/a>"),
"id":integer(202744362520678400),
"to_user_name":string("Rahmadini Hairuddin")
)),
object((
"from_user":string("kelashby"),
"profile_image_url_https":string("https:\\/\\/si0.twimg.com\\/profile_images\\/1861086809\\/me_beach_normal.JPG"),
"to_user_id":integer(0),
"from_user_id_str":string("291446599"),
"geo":null(),
"profile_image_url":string("http:\\/\\/a0.twimg.com\\/profile_images\\/1861086809\\/me_beach_normal.JPG"),
"to_user_id_str":string("0"),
"from_user_name":string("Kelly Ashby"),
"created_at":string("Wed, 16 May 2012 12:56:25 +0000"),
"id_str":string("202744310872018945"),
"text":string("45 days til freedom! Cannot wait! After Paris: London, maybe Amsterdam, then southern France, then CANADA!!!!"),
"to_user":null(),
"metadata":object(("result_type":string("recent"))),
"iso_language_code":string("en"),
"from_user_id":integer(291446599),
"source":string("<a href="http:\\/\\/mobile.twitter.com" rel="nofollow">Mobile Web<\\/a>"),
"id":integer(202744310872018945),
"to_user_name":null()
)),
object((
"from_user":string("johantolsma"),
"profile_image_url_https":string("https:\\/\\/si0.twimg.com\\/profile_images\\/1961917557\\/image_normal.jpg"),
"to_user_id":integer(0),
"from_user_id_str":string("23632499"),
"geo":null(),
"profile_image_url":string("http:\\/\\/a0.twimg.com\\/profile_images\\/1961917557\\/image_normal.jpg"),
"to_user_id_str":string("0"),
"from_user_name":string("Johan Tolsma"),
"created_at":string("Wed, 16 May 2012 12:56:16 +0000"),
"id_str":string("202744274050236416"),
"text":string("RT #agerolemou: Office space for freelancers in Amsterdam http:\\/\\/t.co\\/6VfHuLeK"),
"to_user":null(),
"metadata":object(("result_type":string("recent"))),
"iso_language_code":string("en"),
"from_user_id":integer(23632499),
"source":string("<a href="http:\\/\\/itunes.apple.com\\/us\\/app\\/twitter\\/id409789998?mt=12" rel="nofollow">Twitter for Mac<\\/a>"),
"id":integer(202744274050236416),
"to_user_name":null()
)),
object((
"from_user":string("hellosophieg"),
"profile_image_url_https":string("https:\\/\\/si0.twimg.com\\/profile_images\\/2213055219\\/image_normal.jpg"),
"to_user_id":integer(0),
"from_user_id_str":string("41153106"),
"geo":null(),
"profile_image_url":string("http:\\/\\/a0.twimg.com\\/profile_images\\/2213055219\\/image_normal.jp...
rascal>js is object;
bool: true
rascal>js.members<0>;
set[str]: {"since_id","refresh_url","page","since_id_str","completed_in","results_per_page","next_page","max_id_str","query","max_id","results"}
rascal>js.members["results_per_page"];
Value: integer(25)
You can then use pattern matching, over the types defined in lang::json::ast::json, to extract the information you need.
The code has a bug. This is the fixed code:
public &T cast(type[&T] tp, value v) throws str {
if (&T tv := v)
return tv;
else
throw "cast failed";
}
Note that we do not wish to include this in the standard library. Rather lets collect cases where we need it and find out how to fix it in another way.
If you find you need this casting often, then you might be avoiding the better parts of Rascal, such as pattern based dispatch. See also the answer by Mark Hills.
So, in Haskell, it's really easy to do this:
data Foo = Bar | Baz
deriving (Read, Show)
This is great, but I'd like to be able to pass some data as a string from Haskell to the Elm language. The languages are similar enough that, if I had a Haskell implementation of Read, I could easily convert it to Elm by hand.
The problem is, when I use deriving, the function is automatically generated, but I can't actually see what it does.
I'm wondering, is there a way to automatically generate the code for parsing and showing using Read and Show, so that I could actually see the code itself?
You can use the the -ddump-deriv GHC option to see the code for derived instances:
ghc -ddump-deriv test.hs
[1 of 1] Compiling Test ( test.hs, test.o )
==================== Derived instances ====================
Derived instances:
instance GHC.Show.Show Test.FooBar where
GHC.Show.showsPrec _ Test.Foo = GHC.Show.showString "Foo"
GHC.Show.showsPrec _ Test.Bar = GHC.Show.showString "Bar"
GHC.Show.showList = GHC.Show.showList__ (GHC.Show.showsPrec 0)
Generic representation:
Generated datatypes for meta-information:
Representation types:
For stack:
stack build --ghc-options="-ddump-deriv"
Output in my specific case is: .stack-work/dist/x86_64-linux-nix/Cabal-2.4.0.1/build/app/app-tmp/src/
For our master project at university we created multiple DSLs using Xtext. One of the DSLs is a model entity DSL which allows the user to create a class with properties and methods.
We reuse Xbase because, of course, we want the methods to have a real programming language without reinventing the wheel:
grammar … with org.eclipse.xtext.xbase.Xbase
generate …
EntityModel:
'package' importedNamespace=QualifiedName
…
implementation=Entity;
Entity:
'entity' name=ValidID '{'
features+=Feature*
'}';
Feature:
LocalVariable | …;
LocalVariable:
'var' (isStatic?='static')? name=ValidID ':' type=JvmTypeReference;
For some reason, even though the type of the LocalVariable is set to JvmTypeReference, when using String (in an actual implementation), it will always show the error
Xtext: Couldn't resolve reference to JvmType 'String'
package com.example
Entity foo {
var bar: String
}
We already tried using a ImportedNamespaceAwareLocalScopeProvider which in getImportedNamespaceResolvers adds java.lang.* like that:
List<ImportNormalizer> implicitImports = super.getImportedNamespaceResolvers(context, ignoreCase);
List<ImportNormalizer> javaLangImports = singletonList(new ImportNormalizer(QualifiedName.create("java", "lang"), true, ignoreCase));
implicitImports.addAll(javaLangImports);
return implicitImports;
Even thought that method is called a lot of times, the imports still don't work. When inspecting the EObject context parameter, it sometimes returns java.lang.String (which I guess is for the JvmTypeReference but it still displays an error.
In the RuntimeModule the new scope provider is configured like that:
public void configureIScopeProviderDelegate(com.google.inject.Binder binder) {
binder.bind(org.eclipse.xtext.scoping.IScopeProvider.class).annotatedWith(com.google.inject.name.Names.named(org.eclipse.xtext.scoping.impl.AbstractDeclarativeScopeProvider.NAMED_DELEGATE)).to(MasterDSLImportedNamespaceAwareLocalScopeProvider.class);
}
In the Workflow we configured
fragment = scoping.ImportNamespacesScopingFragment {}
fragment = exporting.QualifiedNamesFragment {}
fragment = builder.BuilderIntegrationFragment {}
The rest of the project is quite complex already (4 Xtext DSLs in one project and multiple generators). But except for completely different DSLs, they use almost the same workflow and RuntimeModule configuration. Another DSL also uses JvmTypeReference and also doesn't find e.g. boolean or anything else.
The question of course is: are we doing something wrong or is there something else we have to do. It used to work when we had a significantly smaller project but after some major changes suddenly this stopped working.