scheme_read.c

/*
  libscheme
  Copyright (c) 1994 Brent Benson
  All rights reserved.

  Permission is hereby granted, without written agreement and without
  license or royalty fees, to use, copy, modify, and distribute this
  software and its documentation for any purpose, provided that the
  above copyright notice and the following two paragraphs appear in
  all copies of this software.

  IN NO EVENT SHALL BRENT BENSON BE LIABLE TO ANY PARTY FOR DIRECT,
  INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT
  OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN IF BRENT
  BENSON HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

  BRENT BENSON SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT
  NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
  FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER
  IS ON AN "AS IS" BASIS, AND BRENT BENSON HAS NO OBLIGATION TO
  PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR
  MODIFICATIONS.
*/

#include "scheme.h"
#include <stdlib.h>
#include <ctype.h>

#define MAX_STRING_SIZE 1024
#define MAX_NUMBER_SIZE 64
#define MAX_SYMBOL_SIZE 255

/* static function declarations */

static Scheme_Value read_char (Scheme_Value port);
static Scheme_Value read_list (Scheme_Value port);
static Scheme_Value read_string (Scheme_Value port);
static Scheme_Value read_quote (Scheme_Value port);
static Scheme_Value read_vector (Scheme_Value port);
static Scheme_Value read_number (Scheme_Value port);
static Scheme_Value read_hex_number (Scheme_Value port);
static Scheme_Value read_binary_number (Scheme_Value port);
static Scheme_Value read_octal_number (Scheme_Value port);
static Scheme_Value read_symbol (Scheme_Value port);
static Scheme_Value read_character (Scheme_Value port);
static Scheme_Value read_quasiquote (Scheme_Value port);
static Scheme_Value read_unquote (Scheme_Value port);
static Scheme_Value read_unquote_splicing (Scheme_Value port);
static void skip_whitespace_comments (Scheme_Value port);
static int peek_char (Scheme_Value port);
static int double_peek_char (Scheme_Value port);
static int match_chars (Scheme_Value port, char *str);

/* exported functions */

Scheme_Value
scheme_read (Scheme_Value port)
{
  int ch;

 start_over:
  ch = scheme_getc (port);
  while (isspace(ch))
    {
      ch = scheme_getc (port);
    }
  switch ( ch )
    {
    case EOF: return (scheme_eof);
    case ')': scheme_signal_error ("read: unexpected ')'");
    case '(': return (read_list (port));
    case '"': return (read_string (port));
    case '\'': return (read_quote (port));
    case '`': return (read_quasiquote (port));
    case ',':
      if (peek_char (port) == '@')
	{
	  ch = scheme_getc (port);
	  return (read_unquote_splicing (port));
	}
      else
	{
	  return (read_unquote (port));
	}
    case ';':
      while ((ch = scheme_getc (port)) != '\n')
	{
	  if (ch == EOF)
	    {
	      return (scheme_eof);
	    }
	}
      goto start_over;
    case '+':
    case '-':
      if (isdigit (peek_char (port)))
	{
	  scheme_ungetc (ch, port);
	  return (read_number (port));
	}
      else
	{
	  scheme_ungetc (ch, port);
	  return (read_symbol (port));
	}
    case '#':
      ch = scheme_getc (port);
      switch ( ch )
	{
	case '(': return (read_vector (port));
	case '\\': return (read_character (port));
	case 't': return (scheme_true);
	case 'f': return (scheme_false);
	case 'x': return (read_hex_number (port));
	case 'b': return (read_binary_number (port));
	case 'o': return (read_octal_number (port));
	case '|':
	  do
	    {
	      ch = scheme_getc (port);
	      if (ch == EOF)
		{
		  scheme_signal_error ("read: end of file in #| comment");
		}
	      if ((ch == '|') && (peek_char(port) == '#'))
		{
		  ch = scheme_getc (port);
		  goto start_over;
		}
	    }
	  while ( 1 );
	  break;
	default:
	  scheme_signal_error ("read: unexpected `#'");
	}
    default:
      if (isdigit (ch))
	{
	  scheme_ungetc (ch, port);
	  return (read_number (port));
	}
      else
	{
	  scheme_ungetc (ch, port);
	  return (read_symbol (port));
	}
    }
}

/* static functions */

/* read any character */
static Scheme_Value
read_char (Scheme_Value port)
{
  int ch;

  ch = scheme_getc (port);
  if (ch == EOF)
    {
      return (scheme_eof);
    }
  else
    {
      return (scheme_make_char (ch));
    }
}

/* "(" has already been read */
static Scheme_Value
read_list (Scheme_Value port)
{
  Scheme_Value car, cdr;

  skip_whitespace_comments (port);
  if (peek_char(port) == ')')
    {
      scheme_getc (port);
      return (scheme_null);
    }
  car = scheme_read (port);
  skip_whitespace_comments (port);
  if (peek_char(port) == ')')
    {
      scheme_getc (port);
      cdr = scheme_null;
    }
  else if ((peek_char(port) == '.') && isspace (double_peek_char(port)))
    {
      scheme_getc (port);
      cdr = scheme_read (port);
      skip_whitespace_comments (port);
      if (peek_char(port) != ')')
	{
	  scheme_signal_error ("read: malformed list");
	}
      scheme_getc (port);
    }
  else
    {
      cdr = read_list (port);
    }
  return (scheme_make_pair (car, cdr));
}

/* '"' has already been read */
static Scheme_Value
read_string (Scheme_Value port)
{
  char ch, buf[MAX_STRING_SIZE];
  int i;

  i = 0;
  while ((ch = scheme_getc (port)) != '"')
    {
      if (ch == '\\')
	{
	  ch = scheme_getc (port);
	}
      if (i > MAX_STRING_SIZE)
	{
	  scheme_signal_error ("read: string too long for reader");
	}
      buf[i++] = ch;
    }
  buf[i] = '\0';
  return (scheme_make_string (buf));
}

/* "'" has been read */
static Scheme_Value
read_quote (Scheme_Value port)
{
  Scheme_Value obj;

  obj = scheme_read (port);
  return (scheme_make_pair (scheme_quote_symbol,
			    scheme_make_pair (obj, scheme_null)));
}

/* "#(" has been read */
static Scheme_Value
read_vector (Scheme_Value port)
{
  Scheme_Value obj, vec;
  int len, i;

  obj = read_list (port);
  len = scheme_list_length (obj);
  vec = scheme_make_vector (len, NULL);
  for ( i=0 ; i<len ; ++i )
    {
      SCHEME_VEC_ELS(vec)[i] = SCHEME_CAR(obj);
      obj = SCHEME_CDR(obj);
    }
  return (vec);
}

/* nothing has been read */
static Scheme_Object  *
read_number (Scheme_Value port)
{
  char buf[MAX_NUMBER_SIZE];
  int i, is_float, is_negative, ch;

  i = 0;
  is_negative = is_float = 0;
  ch = scheme_getc (port);
  if (ch == '+')
    {
      ch = scheme_getc (port);
    }
  else if (ch == '-')
    {
      is_negative = 1;
      ch = scheme_getc (port);
    }
  do
    {
      if (i > MAX_NUMBER_SIZE)
	{
	  scheme_signal_error ("read: number too long for reader");
	}
      if ((ch == '.') || (ch == 'e') || (ch == 'E'))
	{
	  is_float = 1;
	}
      buf[i++] = ch;
    }
  while (isdigit (ch = scheme_getc (port)) || (ch == '.') || (ch == 'e') || (ch == 'E'));
  scheme_ungetc (ch, port);
  buf[i] = '\0';
  if ( is_float )
    {
      double d;
      d = strtod (buf, NULL);
      if (is_negative)
	{
	  d = -d;
	}
      return (scheme_make_double (d));
    }
  else
    {
      int i;

      i = atoi (buf);
      if (is_negative)
	{
	  i = -i;
	}
      return (scheme_make_integer (i));
    }
}

static Scheme_Value
read_hex_number (Scheme_Value port)
{
  int ch, i;

  i = 0;
  while ( 1 )
    {
      ch = scheme_getc (port);
      if (ch >= '0' && ch <= '9')
	{
	  i *= 16;
	  i += ch - '0';
	}
      else if ((ch >= 'a' && ch <= 'f') || (ch >= 'A' && ch <= 'F'))
	{
	  i *= 16;
	  if (ch >= 'a' && ch <= 'f')
	    i += ch - 'a' + 10;
	  else
	    i += ch - 'A' + 10;
	}
      else
	{
	  scheme_ungetc (ch, port);
	  return (scheme_make_integer (i));
	}
    }
}

static Scheme_Value
read_binary_number (Scheme_Value port)
{
  int ch, i;

  i = 0;
  while ( 1 )
    {
      ch = scheme_getc (port);
      if (ch == '0' || ch == '1')
	{
	  i *= 2;
	  i += ch - '0';
	}
      else
	{
	  scheme_ungetc (ch, port);
	  return (scheme_make_integer (i));
	}
    }
}

static Scheme_Value
read_octal_number (Scheme_Value port)
{
  int ch, i;

  i = 0;
  while ( 1 )
    {
      ch = scheme_getc (port);
      if (ch >= '0' && ch <= '7')
	{
	  i *= 8;
	  i += ch - '0';
	}
      else
	{
	  scheme_ungetc (ch, port);
	  return (scheme_make_integer (i));
	}
    }
}

/* nothing has been read */
static Scheme_Value
read_symbol (Scheme_Value port)
{
  char buf[MAX_SYMBOL_SIZE];
  int i, ch;

  i = 0;
  while ((!isspace (ch = scheme_getc (port)))
	 && (ch != '(')
	 && (ch != ')')
	 && (ch != '"')
	 && (ch != ';')
	 && (ch != EOF))
    {
      buf[i++] = ch;
    }
  if (ch != EOF)
    {
      scheme_ungetc (ch, port);
    }
  buf[i] = '\0';
  return (scheme_intern_symbol ((char *)&buf));
}

/* "#\" has been read */
static Scheme_Value
read_character (Scheme_Value port)
{
  int ch;

  ch = scheme_getc (port);
  switch (ch)
    {
    case 'n': /* maybe `newline' */
    case 'N':
      if ((peek_char(port) == 'e') || (peek_char(port) == 'E'))
	{
	  if (! match_chars (port, "ewline"))
	    {
	      scheme_signal_error ("read: bad character constant");
	    }
	  else
	    {
	      return (scheme_make_char ('\n'));
	    }
	}
      else
	{
	    return (scheme_make_char (ch));
	}
    case 's': /* maybe `space' */
    case 'S':
      if ((peek_char(port) == 'p') || (peek_char(port) == 'P'))
	{
	  if (! match_chars (port, "pace"))
	    {
	      scheme_signal_error ("read: bad character constant");
	    }
	  else
	    {
	      return (scheme_make_char (' '));
	    }
	}
      else
	{
	  return (scheme_make_char (ch));
	}
    case 'r': /* maybe `rubout' */
    case 'R':
      if ((peek_char(port) == 'u') || (peek_char(port) == 'U'))
	{
	  if (! match_chars (port, "ubout"))
	    {
	      scheme_signal_error ("read: bad character constant");
	    }
	  else
	    {
	      return (scheme_make_char (0x7f));
	    }
	}
      else if ((peek_char(port) == 'e') || (peek_char(port) == 'E'))
	{
	  if (! match_chars (port, "eturn"))
	    {
	      scheme_signal_error ("read: bad character constant");
	    }
	  else
	    {
	      return (scheme_make_char ('\r'));
	    }
	}
      else
	{
	  return (scheme_make_char (ch));
	}
    case 'p': /* maybe `page' */
    case 'P':
      if ((peek_char(port) == 'a') || (peek_char(port) == 'A'))
	{
	  if (! match_chars (port, "age"))
	    {
	      scheme_signal_error ("read: bad character constant");
	    }
	  else
	    {
	      return (scheme_make_char ('\f'));
	    }
	}
      else
	{
	  return (scheme_make_char (ch));
	}
    case 't': /* maybe `tab' */
    case 'T':
      if ((peek_char(port) == 'a') || (peek_char(port) == 'A'))
	{
	  if (! match_chars (port, "ab"))
	    {
	      scheme_signal_error ("read: bad character constant");
	    }
	  else
	    {
	      return (scheme_make_char ('\t'));
	    }
	}
      else
	{
	  return (scheme_make_char (ch));
	}
    case 'b': /* maybe `backspace' */
    case 'B':
      if ((peek_char(port) == 'a') || (peek_char(port) == 'A'))
	{
	  if (! match_chars (port, "ackspace"))
	    {
	      scheme_signal_error ("read: bad character constant", NULL);
	    }
	  else
	    {
	      return (scheme_make_char ('\b'));
	    }
	}
      else
	{
	  return (scheme_make_char (ch));
	}
    case 'l': /* maybe `linefeed' */
    case 'L':
      if ((peek_char(port) == 'i') || (peek_char(port) == 'I'))
	{
	  if (! match_chars (port, "inefeed"))
	    {
	      scheme_signal_error ("read: bad character constant");
	    }
	  else
	    {
	      return (scheme_make_char ('\n'));
	    }
	}
      else
	{
	  return (scheme_make_char (ch));
	}
    default:
      return (scheme_make_char (ch));
    }
}

/* "`" has been read */
static Scheme_Value
read_quasiquote (Scheme_Value port)
{
  Scheme_Value quoted_obj, ret;

  quoted_obj = scheme_read (port);
  ret = scheme_make_pair (scheme_quasiquote_symbol,
			  scheme_make_pair (quoted_obj, scheme_null));
  return (ret);
}

/* "," has been read */
static Scheme_Value
read_unquote (Scheme_Value port)
{
  Scheme_Value obj, ret;

  obj = scheme_read (port);
  ret = scheme_make_pair (scheme_unquote_symbol,
			  scheme_make_pair (obj, scheme_null));
  return (ret);
}

/* ",@" has been read */
static Scheme_Value
read_unquote_splicing (Scheme_Value port)
{
  Scheme_Value obj, ret;

  obj = scheme_read (port);
  ret = scheme_make_pair (scheme_unquote_splicing_symbol,
			  scheme_make_pair (obj, scheme_null));
  return (ret);
}

/* utilities */

static void
skip_whitespace_comments (Scheme_Value port)
{
  int ch;

 start_over:
  while (isspace(ch = scheme_getc (port)));
  if ( ch == ';' )
    {
      while ((ch = scheme_getc (port)) != '\n');
      goto start_over;
    }
  scheme_ungetc (ch, port);
}

static int
peek_char (Scheme_Value port)
{
  int ch;

  ch = scheme_getc (port);
  scheme_ungetc (ch, port);
  return (ch);
}

static int
double_peek_char (Scheme_Value port)
{
  int ch1, ch2;

  ch1 = scheme_getc (port);
  ch2 = scheme_getc (port);
  scheme_ungetc (ch2, port);
  scheme_ungetc (ch1, port);
  return (ch2);
}

static int
match_chars (Scheme_Value port, char *str)
{
  int i;
  int ch;

  i = 0;
  while (str[i])
    {
      ch = scheme_getc (port);
      if (tolower(ch) != tolower(str[i]))
	{
	  return (0);
	}
      i++;
    }
  return (1);
}