rego::BuiltInDef Struct Reference

#include <rego.hh>

Public Member Functions
	BuiltInDef (Location name_, std::size_t arity_, BuiltInBehavior behavior_)
virtual void	clear ()

Static Public Member Functions
static BuiltIn	create (const Location &name, std::size_t arity, BuiltInBehavior behavior)

Public Attributes
Location	name
std::size_t	arity
BuiltInBehavior	behavior

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));
}

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("add"), 2, add))

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

Constructor & Destructor Documentation

BuiltInDef()

rego::BuiltInDef::BuiltInDef	(	Location	name_,
		std::size_t	arity_,
		BuiltInBehavior	behavior_ )

Constructor.

Member Function Documentation

clear()

virtual void rego::BuiltInDef::clear ( )

virtual

Called to clear any persistent state or caching.

create()

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

static

Creates a new built-in.

BuiltIn is a pointer to a BuiltInDef.

Parameters

name	The name of the built-in.
arity	The number of arguments expected by the built-in.
behavior	The function which will be called when the built-in is evaluated.

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.

behavior

BuiltInBehavior rego::BuiltInDef::behavior

The function which will be called when the built-in is evaluated.

name

Location rego::BuiltInDef::name

The name used to match against expression calls in the rego program.

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

• include/rego/rego.hh