/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * This file is part of MiniBasic.                                 *
 * See the file "MiniBasic-LICENSE" for Copyright information and  *
 * the terms and conditions for copying, distribution and          *
 * modification of MiniBasic.                                      *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

Package minibasic;

Helpers
  letter = ['A'..'Z'];
  digit  = ['0'..'9'];
  cr = 13;
  lf = 10;
  not_cr_lf = [[32..127] - [cr + lf]];

Tokens
  if    = 'IF';
  then  = 'THEN';
  else  = 'ELSE';
  endif = 'ENDIF';

  for  = 'FOR';
  to   = 'TO';
  next = 'NEXT';

  read    = 'READ';
  print   = 'PRINT';
  println = 'PRINTLN';

  assign = ':=';

  less_than    = '<';
  greater_than = '>';
  equal        = '=';

  plus  = '+';
  minus = '-';
  mult  = '*';
  div   = '/';
  mod   = '%';

  l_par = '(';
  r_par = ')';

  identifier = letter (letter | digit)*;
  number     = digit+;
  string     = '"' [not_cr_lf - '"']* '"';

  new_line = cr | lf | cr lf;

  blank = ' '*;

Ignored Tokens
  blank;

Productions
  statements = 
    {list}  statement statements | 
    {empty} ;

  statement = 
    {if}         if condition then [nl1]:new_line
                   statements
                   optional_else
                 endif [nl2]:new_line |

    {for}        for identifier assign [from_exp]:expression to [to_exp]:expression [nl1]:new_line
                   statements
                 next [nl2]:new_line |

    {read}       read identifier new_line |

    {print_exp}  print expression new_line |
    {print_str}  print string new_line |
    {println}    println new_line |

    {assignment} identifier assign expression new_line;

  optional_else = 
    {else}  else new_line
              statements |
    {empty} ;
  
  condition =
    {less_than}    [left]:expression less_than    [right]:expression |
    {greater_than} [left]:expression greater_than [right]:expression |
    {equal}        [left]:expression equal        [right]:expression;

  expression =
    {value} value |
    {plus}  [left]:value plus  [right]:value |
    {minus} [left]:value minus [right]:value |
    {mult}  [left]:value mult  [right]:value |
    {div}   [left]:value div   [right]:value |
    {mod}   [left]:value mod   [right]:value;

  value =
    {constant}   number |
    {identifier} identifier |
    {expression} l_par expression r_par;