/**
 *  payloads/function.h
 *
 *  an ordinary Lisp function - one whose arguments are pre-evaluated.
 *
 *  (c) 2026 Simon Brooke <simon@journeyman.cc>
 *  Licensed under GPL version 2.0, or, at your option, any later version.
 */

#ifndef __psse_payloads_function_h
#define __psse_payloads_function_h

#include "memory/pointer.h"
#include "memory/pso4.h"

/** 
 * I don't think it's necessary to pass both an unmanaged and a managed
 * frame pointer into a function, but it may prove to be more efficient to do
 * so. For the present we'll assume not. See state of play for 15042026.
 */
#define MANAGED_POINTER_ONLY TRUE

/**
 * @brief Payload of a function cell.
 */
struct function_payload {
    /**
     * pointer to metadata (e.g. the source from which the function was compiled,
     * something to help estimate the cost of the function?).
     */
    struct pso_pointer meta;

#ifdef MANAGED_POINTER_ONLY
    /**  
     * pointer to a C function which takes a managed pointer to the same stack 
     * frame and a managed pointer to the environment as arguments. Arguments
     * to the Lisp function are assumed to be loaded into the frame before
     * invocation.
     */
    struct pso_pointer ( *executable ) ( struct pso_pointer frame_pointer );
#else
    /**  
     * pointer to a C function which takes an unmanaged pointer to a stack frame,
     * a managed pointer to the same stack frame, and a managed pointer to the
     * environment as arguments. Arguments to the Lisp function are assumed to be 
     * loaded into the frame before invocation.
     */
    struct pso_pointer ( *executable ) ( struct pso4 * frame,
                                         struct pso_pointer frame_pointer );
#endif
};

#endif