rego::BuiltInDef Struct Reference

Struct which defines a built-in function. More...

#include <rego.hh>

Public Member Functions
	BuiltInDef (Location name_, Node decl_, BuiltInBehavior behavior_, bool available_)
	Constructor.
virtual void	clear ()
	Called to clear any persistent state or caching.

Static Public Member Functions
static BuiltIn	create (const Location &name, Node decl, BuiltInBehavior behavior)
	Creates a new built-in.
static BuiltIn	create (const Location &name, size_t arity, BuiltInBehavior behavior)
	Creates a new built-in.
static BuiltIn	placeholder (const Location &name, Node decl, const std::string &message)
	Creates a placeholder for a built-in which is not available on this platform.

Public Attributes
Location	name
	The name used to match against expression calls in the rego program.
Node	decl
	The declaration node which adheres to the builtins::wf_decl well-formedness definition.
std::size_t	arity
	The number of expected arguments.
BuiltInBehavior	behavior
	The function which will be called when the built-in is evaluated.
bool	available
	Whether the builtin is available.

Detailed Description

Struct which defines a built-in function.

You can extend Rego by registering your own built-ins. A built-in is a function which is called by Rego during evaluation. Built-ins are called with a vector of Nodes, and return a Node. The vector of Nodes contains the arguments passed to the built-in. The Node returned by the built-in is the result of the built-in's evaluation.

Here is an example built-in which performs addition:

Node add(const Nodes& args)
{
  Node a = unwrap_arg(args, UnwrapOpt(0).types({Int, Float}));
  if(a.type() == Error){
    return a;
  }
 
  Node b = unwrap_arg(args, UnwrapOpt(1).types({Int, Float}));
  if(b.type() == Error){
    return b;
  }
 
  if(a.type() == Int && b.type() == Int)
  {
    return scalar(get_int(a) + get_int(b));
  }
 
  return scalar(get_double(a) + get_double(b));
}
 
Node add_decl =
  bi::Decl << (bi::ArgSeq << (bi::Arg << (bi::Name ^ "a") <<
  bi::Description
                                      << (bi::Type << bi::Number))
                          << (bi::Arg << (bi::Name ^ "b") <<
                          bi::Description
                                      << (bi::Type << bi::Number)))
           << (bi::Result << (bi::Name ^ "result")
                          << (bi::Description ^ "The sum of `a` and `b`.")
                          << (bi::Type << bi::Number));

Note that there are several helper methods and objects to aid in writing managing nodes and wrapping/unwrapping them into basic types. Once a method like the above has been written, use BuiltInDef::create following way:

builtins.register_builtin(BuiltInDef::create(Location("myadd"), add_decl,
add))

Then, during evaluation, any call to the built-in myadd will be handled by the myadd function.

Member Function Documentation

create() [1/2]

static BuiltIn rego::BuiltInDef::create ( const Location & name, Node decl, BuiltInBehavior behavior )

static

Creates a new built-in.

The decl node adheres to the builtins::wf_decl well-formedness definition. BuiltIn is a pointer to a BuiltInDef.

Parameters

name	The name of the built-in.
decl	Metadata and documentation for the built-in.
behavior	The function which will be called when the built-in is evaluated.

Returns

The built-in.

create() [2/2]

static BuiltIn rego::BuiltInDef::create ( const Location & name, size_t arity, BuiltInBehavior behavior )

static

Creates a new built-in.

An empty decl node with the correct arity and a return type of Any will be automatically created from the arity argument. ///

Deprecated

Parameters

name	The name of the built-in.
arity	Number of arguments to the builtin
behavior	The function which will be called when the built-in is evaluated.

Returns

The built-in.

placeholder()

static BuiltIn rego::BuiltInDef::placeholder ( const Location & name, Node decl, const std::string & message )

static

Creates a placeholder for a built-in which is not available on this platform.

The decl node adheres to the builtins::wf_decl well-formedness definition. BuiltIn is a pointer to a BuiltInDef.

Parameters

name	The name of the built-in.
decl	Metadata and documentation for the built-in.
message	The message to include in the error when the built-in is called.

Returns

The built-in.

Member Data Documentation

arity

std::size_t rego::BuiltInDef::arity

The number of expected arguments.

If any number of arguments can be provided, use the constant AnyArity.

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The documentation for this struct was generated from the following file:

• include/rego/rego.hh