TODO

- use Sub::Name to set anonymous functions names


# a few shots at getting a usable syntax for
# a source filter variant of the contract declaration

#-------------------------------------
#
# simple way
#
#-------------------------------------

package MyPkg;

use Sub::Contract;

contract('foo',
	       in => [ &valid1, &valid2, a => &valid3, b => &valid4 ],
	       out => [ &valid1, a => &valid3 ],
	       cache => SIZE,
);
# contract_in/out dies if foo already declared previously

sub foo {


    return @aa;
}

# since we have encountered a contract declaration
# for both in and out arguments for foo, 
# source filter replaces foo by:

sub foo {
    Sub::Contract::validate_MyPkg_foo_in(@_);


    return Sub::Contract::validate_MyPkg_foo_out @aa;
}

# in Sub::Contract:

sub UNIVERSAL {
    # called when Sub::Contract::validate_... called from somewhere
    # if ... validator does not exist, create it!
}

# EVAL: 
# - quite efficient: call validate_... only when a contract exists.
# - easy to enable/disable contracts during runtime by putting
#    a 'return if disabled' in beginning of validate_...
# - problem: no support for variable lenght argument lists in contract_in/out
# - a bit hard to parse all perl variants of sub { and return declarations (but
#    not too hard)


#-------------------------------------
#
# the function prototype way
#
#-------------------------------------

sub foo :contract(in => {}, out => {})