// Evaluator definitions
//
// File:	eval.h
// Author:	course
// Version:	1

#ifndef EVAL_H
#define EVAL_H

// The local variable binding environment.  A list of
// the form: ((name . binding) ...) where the name is a
// symbol and the binding is the local binding of the
// symbol: i.e., the value of the symbol as a local
// variable.
//
extern object * environment;


// Evaluate an s-expression in the current environment.
//
object * eval_sexpr (object * sexpr);


// Apply a function object to an argument list.  The
// function object may be a primitive non-special
// function, or a list beginning with LAMBDA,
// LAMBDA-CLOSURE, or MACRO.  The environment is set to
// NIL, except in the case of a LAMBDA-CLOSURE where the
// environment is set from the LAMBDA-CLOSURE.
//
// Both arguments to apply are preserved.  The original
// environment is saved and restored.
//
object * apply (object * function, object * arglist);


// Take a function argument given to prim_funcall,
// prim_apply, or the like and make it ready to pass to
// apply; insists on being given a LAMBDA list,
// primitive (non-special) function, LAMBDA_CLOSURE, or
// a symbol with one of these as its global function
// binding; and calls error in other cases.
//
// Returns the function binding of a symbol, or the
// argument itself if that is not a symbol.
//
// Check_funarg does NO memory allocation.
//
object * check_funarg (object * funarg);


// Return a pointer to the symbol's current binding,
// giving the symbol's current environment binding if
// any, and otherwise the symbol's global symbol_value
// component.
//
object ** binding_pointer (object * sym);

#endif // EVAL_H