# A 'syntax-directed interpreter' (all execution is a side-effect of parsing).
# Inspired by Dennis Allison's original Tiny BASIC grammar, circa 1975.
# 
# Copyright (c) 2007 by Ian Piumarta
# All rights reserved.
# 
# Permission is hereby granted, free of charge, to any person obtaining a
# copy of this software and associated documentation files (the 'Software'),
# to deal in the Software without restriction, including without limitation
# the rights to use, copy, modify, merge, publish, distribute, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, provided that the above copyright notice(s) and this
# permission notice appear in all copies of the Software.  Acknowledgement
# of the use of this Software in supporting documentation would be
# appreciated but is not required.
# 
# THE SOFTWARE IS PROVIDED 'AS IS'.  USE ENTIRELY AT YOUR OWN RISK.
# 
# Last edited: 2012-04-29 15:14:06 by piumarta on emilia

%{
# include <stdio.h>

  typedef struct line line;

  struct line
  {
    int	  number;
    int	  length;
    char *text;
  };

  line *lines= 0;
  int   numLines= 0;
  int   pc= -1, epc= -1;
  int   batch= 0;

  int nextline(char *buf, int max);

# define min(x, y) ((x) < (y) ? (x) : (y))

# define YY_INPUT(buf, result, max_size)	\
  {						\
    if ((pc >= 0) && (pc < numLines))		\
      {						\
        line *linep= lines+pc++;		\
        result= min(max_size, linep->length);	\
        memcpy(buf, linep->text, result);	\
      }						\
    else					\
      result= nextline(buf, max_size);		\
  }

  union value {
    int		  number;
    char	 *string;
    int		(*binop)(int lhs, int rhs);
  };

# define YYSTYPE union value

  int variables[26];

  void accept(int number, char *line);

  void save(char *name);
  void load(char *name);
  void type(char *name);

  int lessThan(int lhs, int rhs)	{ return lhs <  rhs; }
  int lessEqual(int lhs, int rhs)	{ return lhs <= rhs; }
  int notEqual(int lhs, int rhs)	{ return lhs != rhs; }
  int equalTo(int lhs, int rhs)		{ return lhs == rhs; }
  int greaterEqual(int lhs, int rhs)	{ return lhs >= rhs; }
  int greaterThan(int lhs, int rhs)	{ return lhs >  rhs; }

  int input(void);

  int stack[1024], sp= 0;

  char *help;

  void error(char *fmt, ...);
  int findLine(int n, int create);
%}

line = - s:statement CR
|      - n:number < ( !CR . )* CR >			{ accept(n.number, yytext); }
|      - CR
|      - < ( !CR . )* CR >				{ epc= pc;  error("syntax error"); }
|      - !.						{ exit(0); }

statement = 'print'- expr-list
|           'if'- e1:expression r:relop e2:expression	{ if (!r.binop(e1.number, e2.number)) yythunkpos= 0; }
		'then'- statement
|           'goto'- e:expression			{ epc= pc;  if ((pc= findLine(e.number, 0)) < 0) error("no such line"); }
|           'input'- var-list
|           'let'- v:var EQUAL e:expression		{ variables[v.number]= e.number; }
|           'gosub'- e:expression			{ epc= pc;  if (sp < 1024) stack[sp++]= pc, pc= findLine(e.number, 0); else error("too many gosubs");
							  if (pc < 0) error("no such line"); }
|           'return'-					{ epc= pc;  if ((pc= sp ? stack[--sp] : -1) < 0) error("no gosub"); }
|           'clear'-					{ while (numLines) accept(lines->number, "\n"); }
|           'list'-					{ int i;  for (i= 0;  i < numLines;  ++i) printf("%5d %s", lines[i].number, lines[i].text); }
|           'run'- s:string				{ load(s.string);  pc= 0; }
|           'run'-					{ pc= 0; }
|           'end'-					{ pc= -1;  if (batch) exit(0); }
|           'rem'- ( !CR . )*
|           ('bye'|'quit'|'exit')-			{ exit(0); }
|           'save'- s:string				{ save(s.string); }
|           'load'- s:string				{ load(s.string); }
|           'type'- s:string				{ type(s.string); }
|           'dir'-					{ system("ls *.bas"); }
|           'help'-					{ fprintf(stderr, "%s", help); }

expr-list = ( e:string					{ printf("%s", e.string); }
            | e:expression				{ printf("%d", e.number); }
            )? ( COMMA ( e:string			{ printf("%s", e.string); }
                       | e:expression			{ printf("%d", e.number); }
                       )
               )* ( COMMA
	          | !COMMA				{ printf("\n"); }
		  )

var-list = v:var					{ variables[v.number]= input(); }
           ( COMMA v:var				{ variables[v.number]= input(); }
           )*

expression = ( PLUS? l:term
             | MINUS l:term				{ l.number = -l.number }
             ) ( PLUS  r:term				{ l.number += r.number }
               | MINUS r:term				{ l.number -= r.number }
               )*					{ $$.number = l.number }

term = l:factor ( STAR  r:factor			{ l.number *= r.number }
                | SLASH r:factor			{ l.number /= r.number }
                )*					{ $$.number = l.number }

factor = v:var						{ $$.number = variables[v.number] }
|        n:number
|        OPEN expression CLOSE

var = < [a-z] > -					{ $$.number = yytext[0] - 'a' }

number = < digit+ > -					{ $$.number = atoi(yytext); }

digit = [0-9]

string = '"' < [^\"]* > '"' -				{ $$.string = yytext; }

relop = '<=' -						{ $$.binop= lessEqual; }
|       '<>' -						{ $$.binop= notEqual; }
|       '<'  -						{ $$.binop= lessThan; }
|       '>=' -						{ $$.binop= greaterEqual; }
|       '>'  -						{ $$.binop= greaterThan; }
|       '='  -						{ $$.binop= equalTo; }

EQUAL  = '=' -  CLOSE  = ')' -  OPEN   = '(' -
SLASH  = '/' -  STAR   = '*' -  MINUS  = '-' -
PLUS   = '+' -  COMMA  = ',' -

- = [ \t]*

CR = '\n' | '\r' | '\r\n'

%%

#include <unistd.h>
#include <stdarg.h>

char *help=
  "print <num>|<string> [, <num>|<string> ...] [,]\n"
  "if <expr> <|<=|<>|=|>=|> <expr> then <stmt>\n"
  "input <var> [, <var> ...]     let <var> = <expr>\n"
  "goto <expr>                   gosub <expr>\n"
  "end                           return\n"
  "list                          clear\n"
  "run [\"filename\"]              rem <comment...>\n"
  "dir                           type \"filename\"\n"
  "save \"filename\"               load \"filename\"\n"
  "bye|quit|exit                 help\n"
  ;

void error(char *fmt, ...)
{
  va_list ap;
  va_start(ap, fmt);
  if (epc > 0)
    fprintf(stderr, "\nline %d: %s", lines[epc-1].number, lines[epc-1].text);
  else
    fprintf(stderr, "\n");
  vfprintf(stderr, fmt, ap);
  fprintf(stderr, "\n");
  va_end(ap);
  epc= pc= -1;
}

#ifdef USE_READLINE
# include <readline/readline.h>
# include <readline/history.h>
#endif

int nextline(char *buf, int max)
{
  pc= -1;
  if (batch) exit(0);
  if (isatty(fileno(stdin)))
    {
#    ifdef USE_READLINE
      char *line= readline(">");
      if (line)
	{
	  int len= strlen(line);
	  if (len >= max) len= max - 1;
	  strncpy(buf, line, len);
	  (buf)[len]= '\n';
	  add_history(line);
	  free(line);
	  return len + 1;
	}
      else
	{
	  printf("\n");
	  return 0;
	}
#    endif
      putchar('>');
      fflush(stdout);
    }
  return fgets(buf, max, stdin) ? strlen(buf) : 0;
}

int maxLines= 0;

int findLine(int n, int create)
{
  int lo= 0, hi= numLines - 1;
  while (lo <= hi)
    {
      int mid= (lo + hi) / 2, lno= lines[mid].number;
      if (lno > n)
	hi= mid - 1;
      else if (lno < n)
	lo= mid + 1;
      else
	return mid;
    }
  if (create)
    {
      if (numLines == maxLines)
	{
	  maxLines *= 2;
	  lines= realloc(lines, sizeof(line) * maxLines);
	}
      if (lo < numLines)
	memmove(lines + lo + 1, lines + lo, sizeof(line) * (numLines - lo));
      ++numLines;
      lines[lo].number= n;
      lines[lo].text= 0;
      return lo;
    }
  return -1;
}

void accept(int n, char *s)
{
  if (s[0] < 32)	/* delete */
    {
      int lno= findLine(n, 0);
      if (lno >= 0)
	{
	  if (lno < numLines - 1)
	    memmove(lines + lno, lines + lno + 1, sizeof(line) * (numLines - lno - 1));
	  --numLines;
	}
    }
  else			/* insert */
    {
      int lno= findLine(n, 1);
      if (lines[lno].text) free(lines[lno].text);
      lines[lno].length= strlen(s);
      lines[lno].text= strdup(s);
    }
}

char *extend(char *name)
{
  static char path[1024];
  int len= strlen(name);
  sprintf(path, "%s%s", name, (((len > 4) && !strcasecmp(".bas", name + len - 4)) ? "" : ".bas"));
  return path;
}

void save(char *name)
{
  FILE *f= fopen(name= extend(name), "w");
  if (!f)
    perror(name);
  else
    {
      int i;
      for (i= 0;  i < numLines;  ++i)
	fprintf(f, "%d %s", lines[i].number, lines[i].text);
      fclose(f);
    }
}

void load(char *name)
{
  FILE *f= fopen(name= extend(name), "r");
  if (!f)
    perror(name);
  else
    {
      int  lineNumber;
      char lineText[1024];
      while ((1 == fscanf(f, " %d ", &lineNumber)) && fgets(lineText, sizeof(lineText), f))
	accept(lineNumber, lineText);
      fclose(f);
    }
}

void type(char *name)
{
  FILE *f= fopen(name= extend(name), "r");
  if (!f)
    perror(name);
  else
    {
      int  c, d;
      while ((c= getc(f)) >= 0)
	putchar(d= c);
      fclose(f);
      if ('\n' != d && '\r' != d) putchar('\n');
    }
}

int input(void)
{
  char line[32];
  fgets(line, sizeof(line), stdin);
  return atoi(line);
}

int main(int argc, char **argv)
{
  lines= malloc(sizeof(line) * (maxLines= 32));
  numLines= 0;

  if (argc > 1)
    {
      batch= 1;
      while (argc-- > 1)
	load(*++argv);
      pc= 0;
    }

  while (!feof(stdin))
    yyparse();

  return 0;
}