guile/libguile/memoize.c

/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2003,2004,2005,2006,2007,2008,2009
 * Free Software Foundation, Inc.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA
 */



#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <alloca.h>

#include "libguile/__scm.h"

#include <assert.h>
#include "libguile/_scm.h"
#include "libguile/continuations.h"
#include "libguile/eq.h"
#include "libguile/list.h"
#include "libguile/macros.h"
#include "libguile/memoize.h"
#include "libguile/modules.h"
#include "libguile/srcprop.h"
#include "libguile/ports.h"
#include "libguile/print.h"
#include "libguile/strings.h"
#include "libguile/throw.h"
#include "libguile/validate.h"





#if 0
#define CAR(x)   SCM_CAR(x)
#define CDR(x)   SCM_CDR(x)
#define CAAR(x)  SCM_CAAR(x)
#define CADR(x)  SCM_CADR(x)
#define CDAR(x)  SCM_CDAR(x)
#define CDDR(x)  SCM_CDDR(x)
#define CADDR(x) SCM_CADDR(x)
#define CDDDR(x) SCM_CDDDR(x)
#define CADDDR(x) SCM_CDDDR(x)
#else
#define CAR(x)   scm_car(x)
#define CDR(x)   scm_cdr(x)
#define CAAR(x)  scm_caar(x)
#define CADR(x)  scm_cadr(x)
#define CDAR(x)  scm_cdar(x)
#define CDDR(x)  scm_cddr(x)
#define CADDR(x) scm_caddr(x)
#define CDDDR(x) scm_cdddr(x)
#define CADDDR(x) scm_cadddr(x)
#endif


static const char s_bad_expression[] = "Bad expression";
static const char s_expression[] = "Missing or extra expression in";
static const char s_missing_expression[] = "Missing expression in";
static const char s_extra_expression[] = "Extra expression in";
static const char s_empty_combination[] = "Illegal empty combination";
static const char s_missing_body_expression[] = "Missing body expression in";
static const char s_mixed_body_forms[] = "Mixed definitions and expressions in";
static const char s_bad_define[] = "Bad define placement";
static const char s_missing_clauses[] = "Missing clauses";
static const char s_misplaced_else_clause[] = "Misplaced else clause";
static const char s_bad_case_clause[] = "Bad case clause";
static const char s_bad_case_labels[] = "Bad case labels";
static const char s_duplicate_case_label[] = "Duplicate case label";
static const char s_bad_cond_clause[] = "Bad cond clause";
static const char s_missing_recipient[] = "Missing recipient in";
static const char s_bad_variable[] = "Bad variable";
static const char s_bad_bindings[] = "Bad bindings";
static const char s_bad_binding[] = "Bad binding";
static const char s_duplicate_binding[] = "Duplicate binding";
static const char s_bad_exit_clause[] = "Bad exit clause";
static const char s_bad_formals[] = "Bad formals";
static const char s_bad_formal[] = "Bad formal";
static const char s_duplicate_formal[] = "Duplicate formal";
static const char s_splicing[] = "Non-list result for unquote-splicing";
static const char s_bad_slot_number[] = "Bad slot number";


/* Signal a syntax error.  We distinguish between the form that caused the
 * error and the enclosing expression.  The error message will print out as
 * shown in the following pattern.  The file name and line number are only
 * given when they can be determined from the erroneous form or from the
 * enclosing expression.
 *
 * <filename>: In procedure memoization:
 * <filename>: In file <name>, line <nr>: <error-message> in <expression>.  */

SCM_SYMBOL (syntax_error_key, "syntax-error");

/* The prototype is needed to indicate that the function does not return.  */
static void
syntax_error (const char* const, const SCM, const SCM) SCM_NORETURN;

static void 
syntax_error (const char* const msg, const SCM form, const SCM expr)
{
  SCM msg_string = scm_from_locale_string (msg);
  SCM filename = SCM_BOOL_F;
  SCM linenr = SCM_BOOL_F;
  const char *format;
  SCM args;

  if (scm_is_pair (form))
    {
      filename = scm_source_property (form, scm_sym_filename);
      linenr = scm_source_property (form, scm_sym_line);
    }

  if (scm_is_false (filename) && scm_is_false (linenr) && scm_is_pair (expr))
    {
      filename = scm_source_property (expr, scm_sym_filename);
      linenr = scm_source_property (expr, scm_sym_line);
    }

  if (!SCM_UNBNDP (expr))
    {
      if (scm_is_true (filename))
	{
	  format = "In file ~S, line ~S: ~A ~S in expression ~S.";
	  args = scm_list_5 (filename, linenr, msg_string, form, expr);
	}
      else if (scm_is_true (linenr))
	{
	  format = "In line ~S: ~A ~S in expression ~S.";
	  args = scm_list_4 (linenr, msg_string, form, expr);
	}
      else
	{
	  format = "~A ~S in expression ~S.";
	  args = scm_list_3 (msg_string, form, expr);
	}
    }
  else
    {
      if (scm_is_true (filename))
	{
	  format = "In file ~S, line ~S: ~A ~S.";
	  args = scm_list_4 (filename, linenr, msg_string, form);
	}
      else if (scm_is_true (linenr))
	{
	  format = "In line ~S: ~A ~S.";
	  args = scm_list_3 (linenr, msg_string, form);
	}
      else
	{
	  format = "~A ~S.";
	  args = scm_list_2 (msg_string, form);
	}
    }

  scm_error (syntax_error_key, "memoization", format, args, SCM_BOOL_F);
}


/* Shortcut macros to simplify syntax error handling. */
#define ASSERT_SYNTAX(cond, message, form)		\
  { if (SCM_UNLIKELY (!(cond)))			\
      syntax_error (message, form, SCM_UNDEFINED); }
#define ASSERT_SYNTAX_2(cond, message, form, expr)	\
  { if (SCM_UNLIKELY (!(cond)))			\
      syntax_error (message, form, expr); }




/* {Evaluator memoized expressions}
 */

scm_t_bits scm_tc16_memoized;

#define MAKMEMO(n, args) 	(scm_cell (scm_tc16_memoized | ((n) << 16), (scm_t_bits)(args)))

#define MAKMEMO_BEGIN(exps) \
  MAKMEMO (SCM_M_BEGIN, exps)
#define MAKMEMO_IF(test, then, else_) \
  MAKMEMO (SCM_M_IF, scm_cons (test, scm_cons (then, else_)))
#define MAKMEMO_LAMBDA(nreq, rest, body) \
  MAKMEMO (SCM_M_LAMBDA, scm_cons (SCM_I_MAKINUM (nreq), scm_cons (rest, body)))
#define MAKMEMO_LET(inits, body) \
  MAKMEMO (SCM_M_LET, scm_cons (inits, body))
#define MAKMEMO_QUOTE(exp) \
  MAKMEMO (SCM_M_QUOTE, exp)
#define MAKMEMO_DEFINE(var, val) \
  MAKMEMO (SCM_M_DEFINE, scm_cons (var, val))
#define MAKMEMO_APPLY(exp) \
  MAKMEMO (SCM_M_APPLY, exp)
#define MAKMEMO_CONT(proc) \
  MAKMEMO (SCM_M_CONT, proc)
#define MAKMEMO_CALL_WITH_VALUES(prod, cons) \
  MAKMEMO (SCM_M_CALL_WITH_VALUES, scm_cons (prod, cons))
#define MAKMEMO_CALL(proc, args) \
  MAKMEMO (SCM_M_CALL, scm_cons (proc, args))
#define MAKMEMO_LEX_REF(n) \
  MAKMEMO (SCM_M_LEXICAL_REF, SCM_I_MAKINUM (n))
#define MAKMEMO_LEX_SET(n, val) \
  MAKMEMO (SCM_M_LEXICAL_SET, scm_cons (SCM_I_MAKINUM (n), val))
#define MAKMEMO_TOP_REF(var) \
  MAKMEMO (SCM_M_TOPLEVEL_REF, var)
#define MAKMEMO_TOP_SET(var, val) \
  MAKMEMO (SCM_M_TOPLEVEL_SET, scm_cons (var, val))
#define MAKMEMO_MOD_REF(mod, var, public) \
  MAKMEMO (SCM_M_MODULE_REF, scm_cons (mod, scm_cons (var, public)))
#define MAKMEMO_MOD_SET(val, mod, var, public) \
  MAKMEMO (SCM_M_MODULE_SET, scm_cons (val, scm_cons (mod, scm_cons (var, public))))



/* This table must agree with the list of M_ constants in memoize.h */
static const char *const memoized_tags[] =
{
  "begin",
  "if",
  "lambda",
  "let",
  "quote",
  "define",
  "apply",
  "call-with-current-continuation",
  "call-with-values",
  "call",
  "lexical-ref",
  "lexical-set!",
  "toplevel-ref",
  "toplevel-set!",
  "module-ref",
  "module-set",
};

static int
scm_print_memoized (SCM memoized, SCM port, scm_print_state *pstate)
{
  scm_puts ("#<memoized ", port);
  scm_write (scm_unmemoize_expression (memoized), port);
  scm_puts (">", port);
  return 1;
}

static SCM scm_m_at (SCM xorig, SCM env);
static SCM scm_m_atat (SCM xorig, SCM env);
static SCM scm_m_and (SCM xorig, SCM env);
static SCM scm_m_apply (SCM xorig, SCM env);
static SCM scm_m_begin (SCM xorig, SCM env);
static SCM scm_m_cont (SCM xorig, SCM env);
static SCM scm_m_at_call_with_values (SCM xorig, SCM env);
static SCM scm_m_cond (SCM xorig, SCM env);
static SCM scm_m_define (SCM x, SCM env);
static SCM scm_m_eval_when (SCM xorig, SCM env);
static SCM scm_m_if (SCM xorig, SCM env);
static SCM scm_m_lambda (SCM xorig, SCM env);
static SCM scm_m_let (SCM xorig, SCM env);
static SCM scm_m_letrec (SCM xorig, SCM env);
static SCM scm_m_letstar (SCM xorig, SCM env);
static SCM scm_m_or (SCM xorig, SCM env);
static SCM scm_m_quote (SCM xorig, SCM env);
static SCM scm_m_set_x (SCM xorig, SCM env);





typedef SCM (*t_syntax_transformer) (SCM, SCM);

static t_syntax_transformer
memoize_env_ref_transformer (SCM env, SCM x)
{
  SCM var;
  for (; scm_is_pair (env); env = CDR (env))
    if (scm_is_eq (x, CAR (env)))
      return NULL; /* lexical */

  var = scm_module_variable (env, x);
  if (scm_is_true (var) && scm_is_true (scm_variable_bound_p (var))
      && SCM_MACROP (scm_variable_ref (var)))
    { 
      SCM mac = scm_variable_ref (var);
      if (SCM_IMP (SCM_MACRO_CODE (mac))
          || SCM_TYP7 (SCM_MACRO_CODE (mac)) != scm_tc7_subr_2)
        syntax_error ("bad macro", x, SCM_UNDEFINED);
      else
        return (t_syntax_transformer)SCM_SUBRF (SCM_MACRO_CODE (mac)); /* global macro */
    }
  else
    return NULL; /* anything else */
}

static int
memoize_env_var_is_free (SCM env, SCM x)
{
  for (; scm_is_pair (env); env = CDR (env))
    if (scm_is_eq (x, CAR (env)))
      return 0; /* bound */
  return 1; /* free */
}

static int
memoize_env_lexical_index (SCM env, SCM x)
{
  int i = 0;
  for (; scm_is_pair (env); env = CDR (env), i++)
    if (scm_is_eq (x, CAR (env)))
      return i; /* bound */
  return -1; /* free */
}

static SCM
memoize_env_extend (SCM env, SCM vars)
{
  return scm_append (scm_list_2 (vars, env));
}

static SCM
memoize (SCM exp, SCM env)
{
  if (scm_is_pair (exp))
    {
      SCM CAR;
      t_syntax_transformer trans;
      
      CAR = CAR (exp);
      if (scm_is_symbol (CAR))
        trans = memoize_env_ref_transformer (env, CAR);
      else
        trans = NULL;
      
      if (trans)
        return trans (exp, env);
      else
        {
          SCM args = SCM_EOL;
          for (; scm_is_pair (exp); exp = CDR (exp))
            args = scm_cons (memoize (CAR (exp), env), args);
          if (scm_is_null (exp))
            return MAKMEMO (SCM_M_CALL, scm_reverse_x (args, SCM_UNDEFINED));
          else
            syntax_error ("expected a proper list", exp, SCM_UNDEFINED);
        }
    }
  else if (scm_is_symbol (exp))
    {
      int i = memoize_env_lexical_index (env, exp);
      if (i < 0)
        return MAKMEMO_TOP_REF (exp);
      else
        return MAKMEMO_LEX_REF (i);
    }
  else
    return MAKMEMO_QUOTE (exp);
}

static SCM
memoize_exprs (SCM forms, const SCM env)
{
  SCM ret = SCM_EOL;

  for (; !scm_is_null (forms); forms = CDR (forms))
    ret = scm_cons (memoize (CAR (forms), env), ret);
  return scm_reverse_x (ret, SCM_UNDEFINED);
}

static SCM
memoize_sequence (const SCM forms, const SCM env)
{
  ASSERT_SYNTAX (scm_ilength (forms) >= 1, s_bad_expression,
                 scm_cons (scm_sym_begin, forms));
  return MAKMEMO_BEGIN (memoize_exprs (forms, env));
}



/* Memoization.  */

/* bimacros (built-in macros) have isym codes.
   mmacros don't exist at runtime, they just expand out to more primitive
   forms. */
SCM_SYNTAX (s_at, "@", scm_i_makbimacro, scm_m_at);
SCM_SYNTAX (s_atat, "@@", scm_i_makbimacro, scm_m_atat);
SCM_SYNTAX (s_and, "and", scm_makmmacro, scm_m_and);
SCM_SYNTAX (s_begin, "begin", scm_i_makbimacro, scm_m_begin);
SCM_SYNTAX (s_atcall_cc, "@call-with-current-continuation", scm_i_makbimacro, scm_m_cont);
SCM_SYNTAX (s_at_call_with_values, "@call-with-values", scm_i_makbimacro, scm_m_at_call_with_values);
SCM_SYNTAX (s_cond, "cond", scm_makmmacro, scm_m_cond);
SCM_SYNTAX (s_define, "define", scm_i_makbimacro, scm_m_define);
SCM_SYNTAX (s_eval_when, "eval-when", scm_makmmacro, scm_m_eval_when);
SCM_SYNTAX (s_if, "if", scm_i_makbimacro, scm_m_if);
SCM_SYNTAX (s_lambda, "lambda", scm_i_makbimacro, scm_m_lambda);
SCM_SYNTAX (s_let, "let", scm_i_makbimacro, scm_m_let);
SCM_SYNTAX (s_letrec, "letrec", scm_makmmacro, scm_m_letrec);
SCM_SYNTAX (s_letstar, "let*", scm_makmmacro, scm_m_letstar);
SCM_SYNTAX (s_or, "or", scm_makmmacro, scm_m_or);
SCM_SYNTAX (s_quote, "quote", scm_i_makbimacro, scm_m_quote);
SCM_SYNTAX (s_set_x, "set!", scm_i_makbimacro, scm_m_set_x);
SCM_SYNTAX (s_atapply, "@apply", scm_i_makbimacro, scm_m_apply);


SCM_GLOBAL_SYMBOL (scm_sym_apply, "apply");
SCM_GLOBAL_SYMBOL (scm_sym_arrow, "=>");
SCM_GLOBAL_SYMBOL (scm_sym_at, "@");
SCM_GLOBAL_SYMBOL (scm_sym_atat, "@@");
SCM_GLOBAL_SYMBOL (scm_sym_at_call_with_values, "@call-with-values");
SCM_GLOBAL_SYMBOL (scm_sym_atapply, "@apply");
SCM_GLOBAL_SYMBOL (scm_sym_atcall_cc, "@call-with-current-continuation");
SCM_GLOBAL_SYMBOL (scm_sym_begin, "begin");
SCM_GLOBAL_SYMBOL (scm_sym_case, "case");
SCM_GLOBAL_SYMBOL (scm_sym_cond, "cond");
SCM_GLOBAL_SYMBOL (scm_sym_define, "define");
SCM_GLOBAL_SYMBOL (scm_sym_else, "else");
SCM_GLOBAL_SYMBOL (scm_sym_eval_when, "eval-when");
SCM_GLOBAL_SYMBOL (scm_sym_if, "if");
SCM_GLOBAL_SYMBOL (scm_sym_lambda, "lambda");
SCM_GLOBAL_SYMBOL (scm_sym_let, "let");
SCM_GLOBAL_SYMBOL (scm_sym_letrec, "letrec");
SCM_GLOBAL_SYMBOL (scm_sym_letstar, "let*");
SCM_GLOBAL_SYMBOL (scm_sym_or, "or");
SCM_GLOBAL_SYMBOL (scm_sym_quote, "quote");
SCM_GLOBAL_SYMBOL (scm_sym_set_x, "set!");
SCM_SYMBOL (sym_eval, "eval");
SCM_SYMBOL (sym_load, "load");

SCM_GLOBAL_SYMBOL (scm_sym_unquote, "unquote");
SCM_GLOBAL_SYMBOL (scm_sym_quasiquote, "quasiquote");
SCM_GLOBAL_SYMBOL (scm_sym_uq_splicing, "unquote-splicing");


static SCM
scm_m_at (SCM expr, SCM env SCM_UNUSED)
{
  ASSERT_SYNTAX (scm_ilength (expr) == 3, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (CADR (expr)) > 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_is_symbol (CADDR (expr)), s_bad_expression, expr);

  return MAKMEMO_MOD_REF (CADR (expr), CADDR (expr), SCM_BOOL_T);
}

static SCM
scm_m_atat (SCM expr, SCM env SCM_UNUSED)
{
  ASSERT_SYNTAX (scm_ilength (expr) == 3, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (CADR (expr)) > 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_is_symbol (CADDR (expr)), s_bad_expression, expr);

  return MAKMEMO_MOD_REF (CADR (expr), CADDR (expr), SCM_BOOL_F);
}

static SCM
scm_m_and (SCM expr, SCM env)
{
  const SCM cdr_expr = CDR (expr);

  if (scm_is_null (cdr_expr))
    return MAKMEMO_QUOTE (SCM_BOOL_T);
  ASSERT_SYNTAX (scm_is_pair (cdr_expr), s_bad_expression, expr);

  if (scm_is_null (CDR (cdr_expr)))
    return memoize (CAR (cdr_expr), env);
  else
    return MAKMEMO_IF (memoize (CAR (cdr_expr), env),
                       scm_m_and (cdr_expr, env),
                       MAKMEMO_QUOTE (SCM_BOOL_F));
}

static SCM
scm_m_apply (SCM expr, SCM env)
{
  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) == 2, s_missing_expression, expr);

  return MAKMEMO_APPLY (memoize_exprs (cdr_expr, env));
}

static SCM
scm_m_begin (SCM expr, SCM env)
{
  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 1, s_bad_expression, expr);
  return MAKMEMO_BEGIN (memoize_exprs (cdr_expr, env));
}

static SCM
scm_m_cont (SCM expr, SCM env)
{
  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) == 1, s_expression, expr);

  return MAKMEMO_CONT (memoize (CADR (expr), env));
}

static SCM
scm_m_at_call_with_values (SCM expr, SCM env)
{
  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) == 2, s_expression, expr);

  return MAKMEMO_CALL_WITH_VALUES (memoize (CADR (expr), env),
                                   memoize (CADDR (expr), env));
}

static SCM
scm_m_cond (SCM expr, SCM env)
{
  /* Check, whether 'else or '=> is a literal, i. e. not bound to a value. */
  const int else_literal_p = memoize_env_var_is_free (env, scm_sym_else);
  const int arrow_literal_p = memoize_env_var_is_free (env, scm_sym_arrow);

  const SCM clauses = CDR (expr);
  SCM clause_idx;
  SCM ret, loc;

  ASSERT_SYNTAX (scm_ilength (clauses) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (clauses) >= 1, s_missing_clauses, expr);

  ret = scm_cons (SCM_UNDEFINED, MAKMEMO_QUOTE (SCM_UNSPECIFIED));
  loc = ret;

  for (clause_idx = clauses;
       !scm_is_null (clause_idx);
       clause_idx = CDR (clause_idx))
    {
      SCM test;

      const SCM clause = CAR (clause_idx);
      const long length = scm_ilength (clause);
      ASSERT_SYNTAX_2 (length >= 1, s_bad_cond_clause, clause, expr);

      test = CAR (clause);
      if (scm_is_eq (test, scm_sym_else) && else_literal_p)
	{
	  const int last_clause_p = scm_is_null (CDR (clause_idx));
          ASSERT_SYNTAX_2 (length >= 2,
                           s_bad_cond_clause, clause, expr);
          ASSERT_SYNTAX_2 (last_clause_p,
                           s_misplaced_else_clause, clause, expr);
          SCM_SETCDR (loc,
                      memoize (scm_cons (scm_sym_begin, CDR (clause)), env));
	}
      else if (length >= 2
               && scm_is_eq (CADR (clause), scm_sym_arrow)
               && arrow_literal_p)
        {
          SCM tmp = scm_gensym (scm_from_locale_string ("cond "));
          SCM i;
          SCM new_env = scm_cons (tmp, env);
          ASSERT_SYNTAX_2 (length > 2, s_missing_recipient, clause, expr);
          ASSERT_SYNTAX_2 (length == 3, s_extra_expression, clause, expr);
          i = MAKMEMO_IF (MAKMEMO_LEX_REF (0),
                          MAKMEMO_CALL (memoize (CADDR (clause),
                                                 scm_cons (tmp, new_env)),
                                        scm_list_1 (MAKMEMO_LEX_REF (0))),
                          MAKMEMO_QUOTE (SCM_UNSPECIFIED));
          SCM_SETCDR (loc, 
                      MAKMEMO_LET (scm_list_1 (memoize (CAR (clause), env)),
                                   i));
          env = new_env;
          loc = scm_last_pair (SCM_MEMOIZED_ARGS (i));
	}
      /* FIXME length == 1 case */
      else
        {
          SCM i = MAKMEMO_IF (memoize (CAR (clause), env),
                              memoize (scm_cons (scm_sym_begin, CDR (clause)), env),
                              MAKMEMO_QUOTE (SCM_UNSPECIFIED));
          SCM_SETCDR (loc, i);
          loc = scm_last_pair (SCM_MEMOIZED_ARGS (i));
        }
    }

  return CDR (ret);
}

/* According to Section 5.2.1 of R5RS we first have to make sure that the
   variable is bound, and then perform the `(set! variable expression)'
   operation.  However, EXPRESSION _can_ be evaluated before VARIABLE is
   bound.  This means that EXPRESSION won't necessarily be able to assign
   values to VARIABLE as in `(define foo (begin (set! foo 1) (+ foo 1)))'.  */
static SCM
scm_m_define (SCM expr, SCM env)
{
  const SCM cdr_expr = CDR (expr);
  SCM body;
  SCM variable;

  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 2, s_missing_expression, expr);
  ASSERT_SYNTAX (!scm_is_pair (env), s_bad_define, expr);

  body = CDR (cdr_expr);
  variable = CAR (cdr_expr);

  if (scm_is_pair (variable))
    {
      ASSERT_SYNTAX_2 (scm_is_symbol (CAR (variable)), s_bad_variable, variable, expr);
      return MAKMEMO_DEFINE (CAR (variable),
                             memoize (scm_cons (scm_sym_lambda,
                                                scm_cons (CDR (variable), body)),
                                      env));
    }
  ASSERT_SYNTAX_2 (scm_is_symbol (variable), s_bad_variable, variable, expr);
  ASSERT_SYNTAX (scm_ilength (body) == 1, s_expression, expr);
  return MAKMEMO_DEFINE (variable, memoize (CAR (body), env));
}

static SCM
scm_m_eval_when (SCM expr, SCM env)
{
  ASSERT_SYNTAX (scm_ilength (expr) >= 3, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (CADR (expr)) > 0, s_bad_expression, expr);

  if (scm_is_true (scm_memq (sym_eval, CADR (expr)))
      || scm_is_true (scm_memq (sym_load, CADR (expr))))
    return MAKMEMO_BEGIN (memoize_exprs (CDDR (expr), env));
  else
    return MAKMEMO_QUOTE (SCM_UNSPECIFIED);
}

static SCM
scm_m_if (SCM expr, SCM env SCM_UNUSED)
{
  const SCM cdr_expr = CDR (expr);
  const long length = scm_ilength (cdr_expr);
  ASSERT_SYNTAX (length == 2 || length == 3, s_expression, expr);
  return MAKMEMO_IF (memoize (CADR (expr), env),
                     memoize (CADDR (expr), env),
                     ((length == 3)
                      ? memoize (CADDDR (expr), env)
                      : MAKMEMO_QUOTE (SCM_UNSPECIFIED)));
}

/* A helper function for memoize_lambda to support checking for duplicate
 * formal arguments: Return true if OBJ is `eq?' to one of the elements of
 * LIST or to the CDR of the last cons.  Therefore, LIST may have any of the
 * forms that a formal argument can have:
 *   <rest>, (<arg1> ...), (<arg1> ...  .  <rest>) */
static int
c_improper_memq (SCM obj, SCM list)
{
  for (; scm_is_pair (list); list = CDR (list))
    {
      if (scm_is_eq (CAR (list), obj))
        return 1;
    }
  return scm_is_eq (list, obj);
}

static SCM
scm_m_lambda (SCM expr, SCM env SCM_UNUSED)
{
  SCM formals;
  SCM formals_idx;
  SCM formal_vars = SCM_EOL;
  int nreq = 0;

  const SCM cdr_expr = CDR (expr);
  const long length = scm_ilength (cdr_expr);
  ASSERT_SYNTAX (length >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (length >= 2, s_missing_expression, expr);

  /* Before iterating the list of formal arguments, make sure the formals
   * actually are given as either a symbol or a non-cyclic list.  */
  formals = CAR (cdr_expr);
  if (scm_is_pair (formals))
    {
      /* Dirk:FIXME:: We should check for a cyclic list of formals, and if
       * detected, report a 'Bad formals' error.  */
    }
  else
    {
      ASSERT_SYNTAX_2 (scm_is_symbol (formals) || scm_is_null (formals),
                       s_bad_formals, formals, expr);
    }

  /* Now iterate the list of formal arguments to check if all formals are
   * symbols, and that there are no duplicates.  */
  formals_idx = formals;
  while (scm_is_pair (formals_idx))
    {
      const SCM formal = CAR (formals_idx);
      const SCM next_idx = CDR (formals_idx);
      ASSERT_SYNTAX_2 (scm_is_symbol (formal), s_bad_formal, formal, expr);
      ASSERT_SYNTAX_2 (!c_improper_memq (formal, next_idx),
                       s_duplicate_formal, formal, expr);
      nreq++;
      formal_vars = scm_cons (formal, formal_vars);
      formals_idx = next_idx;
    }
  ASSERT_SYNTAX_2 (scm_is_null (formals_idx) || scm_is_symbol (formals_idx),
                   s_bad_formal, formals_idx, expr);
  if (scm_is_symbol (formals_idx))
    formal_vars = scm_cons (formals_idx, formal_vars);
  return MAKMEMO_LAMBDA (nreq, scm_symbol_p (formals_idx),
                         memoize_sequence (CDDR (expr),
                                           memoize_env_extend (env, formal_vars)));
}

/* Check if the format of the bindings is ((<symbol> <init-form>) ...).  */
static void
check_bindings (const SCM bindings, const SCM expr)
{
  SCM binding_idx;

  ASSERT_SYNTAX_2 (scm_ilength (bindings) >= 0,
                   s_bad_bindings, bindings, expr);

  binding_idx = bindings;
  for (; !scm_is_null (binding_idx); binding_idx = CDR (binding_idx))
    {
      SCM name;         /* const */

      const SCM binding = CAR (binding_idx);
      ASSERT_SYNTAX_2 (scm_ilength (binding) == 2,
                       s_bad_binding, binding, expr);

      name = CAR (binding);
      ASSERT_SYNTAX_2 (scm_is_symbol (name), s_bad_variable, name, expr);
    }
}

/* The bindings, which must have the format ((v1 i1) (v2 i2) ... (vn in)), are
 * transformed to the lists (vn .. v2 v1) and (i1 i2 ... in). If a duplicate
 * variable name is detected, an error is signalled. */
static int
transform_bindings (const SCM bindings, const SCM expr,
                    SCM *const rvarptr, SCM *const initptr)
{
  SCM rvariables = SCM_EOL;
  SCM rinits = SCM_EOL;
  SCM binding_idx = bindings;
  int n = 0;
  for (; !scm_is_null (binding_idx); binding_idx = CDR (binding_idx))
    {
      const SCM binding = CAR (binding_idx);
      const SCM CDR_binding = CDR (binding);
      const SCM name = CAR (binding);
      ASSERT_SYNTAX_2 (scm_is_false (scm_c_memq (name, rvariables)),
                       s_duplicate_binding, name, expr);
      rvariables = scm_cons (name, rvariables);
      rinits = scm_cons (CAR (CDR_binding), rinits);
      n++;
    }
  *rvarptr = rvariables;
  *initptr = scm_reverse_x (rinits, SCM_UNDEFINED);
  return n;
}

/* This function is a helper function for memoize_let.  It transforms
 * (let name ((var init) ...) body ...) into
 * ((letrec ((name (lambda (var ...) body ...))) name) init ...)
 * and memoizes the expression.  It is assumed that the caller has checked
 * that name is a symbol and that there are bindings and a body.  */
static SCM
memoize_named_let (const SCM expr, SCM env)
{
  SCM rvariables;
  SCM inits;
  int nreq;

  const SCM cdr_expr = CDR (expr);
  const SCM name = CAR (cdr_expr);
  const SCM cddr_expr = CDR (cdr_expr);
  const SCM bindings = CAR (cddr_expr);
  check_bindings (bindings, expr);

  nreq = transform_bindings (bindings, expr, &rvariables, &inits);

  env = scm_cons (name, env);
  return MAKMEMO_LET
    (scm_list_1 (MAKMEMO_QUOTE (SCM_UNDEFINED)),
     MAKMEMO_BEGIN
     (scm_list_2 (MAKMEMO_LEX_SET
                  (0,
                   MAKMEMO_LAMBDA
                   (nreq, SCM_BOOL_F,
                    memoize_sequence (CDDDR (expr),
                                      memoize_env_extend (env, rvariables)))),
                  MAKMEMO_CALL (MAKMEMO_LEX_REF (0),
                                memoize_exprs (inits, env)))));
}

/* (let ((v1 i1) (v2 i2) ...) body) with variables v1 .. vn and initializers
 * i1 .. in is transformed to (#@let (vn ... v2 v1) (i1 i2 ...) body).  */
static SCM
scm_m_let (SCM expr, SCM env)
{
  SCM bindings;

  const SCM cdr_expr = CDR (expr);
  const long length = scm_ilength (cdr_expr);
  ASSERT_SYNTAX (length >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (length >= 2, s_missing_expression, expr);

  bindings = CAR (cdr_expr);
  if (scm_is_symbol (bindings))
    {
      ASSERT_SYNTAX (length >= 3, s_missing_expression, expr);
      return memoize_named_let (expr, env);
    }

  check_bindings (bindings, expr);
  if (scm_is_null (bindings))
    return memoize_sequence (CDDR (expr), env);
  else
    {
      SCM rvariables;
      SCM inits;
      transform_bindings (bindings, expr, &rvariables, &inits);
      return MAKMEMO_LET (memoize_exprs (inits, env),
                          memoize_sequence (CDDR (expr),
                                            memoize_env_extend (env, rvariables)));
    }
}

static SCM
scm_m_letrec (SCM expr, SCM env)
{
  SCM bindings;

  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 2, s_missing_expression, expr);

  bindings = CAR (cdr_expr);
  if (scm_is_null (bindings))
    return memoize_sequence (CDDR (expr), env);
  else
    {
      SCM rvariables;
      SCM inits;
      SCM v, i;
      SCM undefs = SCM_EOL;
      SCM vals = SCM_EOL;
      SCM sets = SCM_EOL;
      SCM new_env;
      int offset;
      int n = transform_bindings (bindings, expr, &rvariables, &inits);
      offset = n;
      new_env = memoize_env_extend (env, rvariables);
      for (v = scm_reverse (rvariables), i = inits; scm_is_pair (v);
           v = CDR (v), i = CDR (i), n--)
        {
          undefs = scm_cons (MAKMEMO_QUOTE (SCM_UNDEFINED), undefs);
          vals = scm_cons (memoize (CAR (i), new_env), vals);
          sets = scm_cons (MAKMEMO_LEX_SET ((n-1) + offset,
                                            MAKMEMO_LEX_REF (n-1)),
                           sets);
        }
      return MAKMEMO_LET
        (undefs,
         MAKMEMO_BEGIN (scm_list_2 (MAKMEMO_LET (scm_reverse (vals),
                                                 MAKMEMO_BEGIN (sets)),
                                    memoize_sequence (CDDR (expr),
                                                      new_env))));
    }
}

static SCM
scm_m_letstar (SCM expr, SCM env SCM_UNUSED)
{
  SCM bindings;

  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 2, s_missing_expression, expr);

  bindings = CAR (cdr_expr);
  if (scm_is_null (bindings))
    return memoize_sequence (CDDR (expr), env);
  else
    {
      SCM rvariables;
      SCM variables;
      SCM inits;
      SCM ret, loc;
      transform_bindings (bindings, expr, &rvariables, &inits);
      variables = scm_reverse (rvariables);
      ret = scm_cons (SCM_UNDEFINED, SCM_UNSPECIFIED);
      loc = ret;
      for (; scm_is_pair (variables);
           variables = CDR (variables), inits = CDR (inits))
        { SCM x = MAKMEMO_LET (scm_list_1 (memoize (CAR (inits), env)),
                               MAKMEMO_QUOTE (SCM_UNSPECIFIED));
          SCM_SETCDR (loc, x);
          loc = scm_last_pair (SCM_MEMOIZED_ARGS (x));
          env = scm_cons (CAR (variables), env);
        }
      SCM_SETCDR (loc, memoize_sequence (CDDR (expr), env));
      return CDR (ret);
    }
}

static SCM
scm_m_or (SCM expr, SCM env SCM_UNUSED)
{
  SCM tail = CDR (expr);
  SCM ret, loc;
  const long length = scm_ilength (tail);

  ASSERT_SYNTAX (length >= 0, s_bad_expression, expr);

  ret = scm_cons (SCM_UNDEFINED, SCM_UNSPECIFIED);
  loc = ret;
  for (; scm_is_pair (tail); tail = CDR (tail))
    {
      SCM tmp = scm_gensym (scm_from_locale_string ("cond "));
      SCM x = MAKMEMO_IF (MAKMEMO_LEX_REF (0),
                          MAKMEMO_LEX_REF (0),
                          MAKMEMO_QUOTE (SCM_UNSPECIFIED));
      SCM new_env = scm_cons (tmp, env);
      SCM_SETCDR (loc, MAKMEMO_LET (scm_list_1 (memoize (CAR (tail),
                                                         env)),
                                    x));
      env = new_env;
      loc = scm_last_pair (SCM_MEMOIZED_ARGS (x));
    }
  SCM_SETCDR (loc, MAKMEMO_QUOTE (SCM_BOOL_F));
  return CDR (ret);
}

static SCM
scm_m_quote (SCM expr, SCM env SCM_UNUSED)
{
  SCM quotee;

  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) == 1, s_expression, expr);
  quotee = CAR (cdr_expr);
  return MAKMEMO_QUOTE (quotee);
}

static SCM
scm_m_set_x (SCM expr, SCM env)
{
  SCM variable;
  SCM vmem;

  const SCM cdr_expr = CDR (expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) >= 0, s_bad_expression, expr);
  ASSERT_SYNTAX (scm_ilength (cdr_expr) == 2, s_expression, expr);
  variable = CAR (cdr_expr);
  vmem = memoize (variable, env);
  
  switch (SCM_MEMOIZED_TAG (vmem))
    {
    case SCM_M_LEXICAL_REF:
      return MAKMEMO_LEX_SET (SCM_I_INUM (SCM_MEMOIZED_ARGS (vmem)),
                              memoize (CADDR (expr), env));
    case SCM_M_TOPLEVEL_REF:
      return MAKMEMO_TOP_SET (variable,
                              memoize (CADDR (expr), env));
    case SCM_M_MODULE_REF:
      return MAKMEMO_MOD_SET (memoize (CADDR (expr), env),
                              CAR (SCM_MEMOIZED_ARGS (vmem)),
                              CADR (SCM_MEMOIZED_ARGS (vmem)),
                              CDDR (SCM_MEMOIZED_ARGS (vmem)));
    default:
      syntax_error (s_bad_variable, variable, expr);
    }
}




SCM_DEFINE (scm_memoize_expression, "memoize-expression", 1, 0, 0, 
            (SCM exp),
	    "Memoize the expression @var{exp}.")
#define FUNC_NAME s_scm_memoize_expression
{
  return memoize (exp, scm_current_module ());
}
#undef FUNC_NAME




SCM_SYMBOL (sym_placeholder, "_");

static SCM unmemoize (SCM expr);

static SCM
unmemoize_exprs (SCM exprs)
{
  SCM ret, tail;
  if (scm_is_null (exprs))
    return SCM_EOL;
  ret = scm_list_1 (unmemoize (CAR (exprs)));
  tail = ret;
  for (exprs = CDR (exprs); !scm_is_null (exprs); exprs = CDR (exprs))
    {
      SCM_SETCDR (tail, scm_list_1 (unmemoize (CAR (exprs))));
      tail = CDR (tail);
    }
  return ret;
}

static SCM
unmemoize_bindings (SCM inits)
{
  SCM ret, tail;
  if (scm_is_null (inits))
    return SCM_EOL;
  ret = scm_list_1 (scm_list_2 (sym_placeholder, unmemoize (CAR (inits))));
  tail = ret;
  for (inits = CDR (inits); !scm_is_null (inits); inits = CDR (inits))
    {
      SCM_SETCDR (tail, scm_list_1 (scm_list_2 (sym_placeholder,
                                                unmemoize (CAR (inits)))));
      tail = CDR (tail);
    }
  return ret;
}

static SCM
unmemoize_lexical (SCM n)
{
  char buf[16];
  buf[15] = 0;
  snprintf (buf, 15, "<%u>", scm_to_uint32 (n));
  return scm_from_locale_symbol (buf);
}

static SCM
unmemoize (const SCM expr)
{
  SCM args;
  
  if (!SCM_MEMOIZED_P (expr))
    abort ();

  args = SCM_MEMOIZED_ARGS (expr);
  switch (SCM_MEMOIZED_TAG (expr))
    {
    case SCM_M_APPLY:
      return scm_cons (scm_sym_atapply, unmemoize_exprs (args));
    case SCM_M_BEGIN:
      return scm_cons (scm_sym_begin, unmemoize_exprs (args));
    case SCM_M_CALL:
      return unmemoize_exprs (args);
    case SCM_M_CONT:
      return scm_list_2 (scm_sym_atcall_cc, unmemoize (args));
    case SCM_M_CALL_WITH_VALUES:
      return scm_list_3 (scm_sym_at_call_with_values,
                         unmemoize (CAR (args)), unmemoize (CDR (args)));
    case SCM_M_DEFINE:
      return scm_list_3 (scm_sym_define, CAR (args), unmemoize (CDR (args)));
    case SCM_M_IF:
      return scm_list_4 (scm_sym_if, unmemoize (scm_car (args)),
                         unmemoize (scm_cadr (args)), unmemoize (scm_cddr (args)));
    case SCM_M_LAMBDA:
      return scm_list_3 (scm_sym_lambda,
                         scm_make_list (CAR (args), sym_placeholder),
                         unmemoize (CDDR (args)));
    case SCM_M_LET:
      return scm_list_3 (scm_sym_let,
                         unmemoize_bindings (CAR (args)),
                         unmemoize (CDR (args)));
    case SCM_M_QUOTE:
      return scm_list_2 (scm_sym_quote, args);
    case SCM_M_LEXICAL_REF:
      return unmemoize_lexical (args);
    case SCM_M_LEXICAL_SET:
      return scm_list_3 (scm_sym_set_x, unmemoize_lexical (CAR (args)),
                         unmemoize (CDR (args)));
    case SCM_M_TOPLEVEL_REF:
      return args;
    case SCM_M_TOPLEVEL_SET:
      return scm_list_3 (scm_sym_set_x, CAR (args), unmemoize (CDR (args)));
    case SCM_M_MODULE_REF:
      return scm_list_3 (scm_is_true (CDDR (args)) ? scm_sym_at : scm_sym_atat,
                         scm_i_finite_list_copy (CAR (args)),
                         CADR (args));
    case SCM_M_MODULE_SET:
      return scm_list_3 (scm_sym_set_x,
                         scm_list_3 (scm_is_true (CDDDR (args))
                                     ? scm_sym_at : scm_sym_atat,
                                     scm_i_finite_list_copy (CADR (args)),
                                     CADDR (args)),
                         unmemoize (CAR (args)));
    default:
      abort ();
    }
}

SCM_DEFINE (scm_memoized_p, "memoized?", 1, 0, 0, 
            (SCM obj),
	    "Return @code{#t} if @var{obj} is memoized.")
#define FUNC_NAME s_scm_memoized_p
{
  return scm_from_bool (SCM_MEMOIZED_P (obj));
}
#undef FUNC_NAME

SCM_DEFINE (scm_unmemoize_expression, "unmemoize-expression", 1, 0, 0, 
            (SCM m),
	    "Unmemoize the memoized expression @var{m}.")
#define FUNC_NAME s_scm_unmemoize_expression
{
  SCM_VALIDATE_MEMOIZED (1, m);
  return unmemoize (m);
}
#undef FUNC_NAME




void
scm_init_memoize ()
{
  scm_tc16_memoized = scm_make_smob_type ("%memoized", 0);
  scm_set_smob_mark (scm_tc16_memoized, scm_markcdr);
  scm_set_smob_print (scm_tc16_memoized, scm_print_memoized);

#include "libguile/memoize.x"
}

/*
  Local Variables:
  c-file-style: "gnu"
  End:
*/