# Possible improvements of the rpython language

## Improve the interpreter API

• Rationalize the modules, and the names, of the different functions needed to implement a pypy module. A typical rpython file is likely to contain many import statements:

from pypy.interpreter.baseobjspace import Wrappable
from pypy.interpreter.gateway import ObjSpace, W_Root
from pypy.interpreter.argument import Arguments
from pypy.interpreter.typedef import TypeDef, GetSetProperty
from pypy.interpreter.typedef import interp_attrproperty, interp_attrproperty_w
from pypy.interpreter.gateway import interp2app
from pypy.interpreter.error import OperationError
from pypy.rpython.lltypesystem import rffi, lltype

• A more direct declarative way to write Typedef:

class W_Socket(Wrappable):
_typedef_name_ = 'socket'
_typedef_base_ = W_EventualBaseClass

@interp2app_method("connect", ['self', ObjSpace, W_Root])
...

• Support for metaclasses written in rpython. For a sample, see the skipped test pypy.objspace.std.test.TestTypeObject.test_metaclass_typedef

## RPython language

• Arithmetic with unsigned integer, and between integer of different signedness, when this is not ambiguous. At least, comparison and assignment with constants should be allowed.
• Allocate variables on the stack, and pass their address ("by reference") to llexternal functions. For a typical usage, see pypy.rlib.rsocket.RSocket.getsockopt_int.

## Extensible type system for llexternal

llexternal allows the description of a C function, and conveys the same information about the arguments as a C header. But this is often not enough. For example, a parameter of type int* is converted to rffi.CArrayPtr(rffi.INT), but this information is not enough to use the function. The parameter could be an array of int, a reference to a single value, for input or output...

A "type system" could hold this additional information, and automatically generate some conversion code to ease the usage of the function from rpython. For example:

# double frexp(double x, int *exp);
frexp = llexternal("frexp", [rffi.DOUBLE, OutPtr(rffi.int)], rffi.DOUBLE)


OutPtr indicates that the parameter is output-only, which need not to be initialized, and which value is returned to the caller. In rpython the call becomes:

fraction, exponent = frexp(value)


Also, we could imagine that one item in the llexternal argument list corresponds to two parameters in C. Here, OutCharBufferN indicates that the caller will pass a rpython string; the framework will pass buffer and length to the function:

# ssize_t write(int fd, const void *buf, size_t count);
write = llexternal("write", [rffi.INT, CharBufferAndSize], rffi.SSIZE_T)


The rpython code that calls this function is very simple:

written = write(fd, data)


compared with the present:

count = len(data)
buf = rffi.get_nonmovingbuffer(data)
try:
written = rffi.cast(lltype.Signed, os_write(
rffi.cast(rffi.INT, fd),
buf, rffi.cast(rffi.SIZE_T, count)))
finally:
rffi.free_nonmovingbuffer(data, buf)


Typemaps are very useful for large APIs where the same conversions are needed in many places. XXX example