{ syntax of pascal expressions
   pascal user manual and report, 2nd edition, p.110 et seq }

program: expression, stop symbol.

expression:
  simple expression, expr tail.

expr tail:
  relational operator, expression;
  empty.

relational operator: equals symbol;
  not equals symbol;
  less than symbol;
  less than or equals symbol;
  greater than or equals symbol;
  greater than symbol;
  in symbol.

simple expression:
  term, simple expr tail;
  sign, term, simple expr tail.

simple expr tail:
  adding operator, term, simple expr tail;
  empty.

sign: plus symbol;
  minus symbol.

adding operator: plus symbol;
  minus symbol;
  or symbol.

term: factor, term tail.

term tail:
  multiplying operator, term;
  empty.

multiplying operator: star symbol;
  slash symbol;
  div symbol;
  mod symbol;
  and symbol.

factor: iden symbol;
  numb symbol;
  left paren symbol, expression, right paren symbol;
  set;
  not symbol, factor.

set:
  left bracket symbol, set tail.

set tail:
  element list with comma, right bracket symbol;
  right bracket symbol.

element list with comma:
  element, element list tail.

element list tail:
  comma symbol, element list with comma;
  empty.

element:
  expression, element tail.

element tail:
  dotdot symbol, element;
  empty.

empty: .

iden symbol:                    'a'.
numb symbol:                    '0'.
plus symbol:                    '+'.
minus symbol:                   '-'.
star symbol:                    '*'.
slash symbol:                   '/'.
comma symbol:                   ','.
equals symbol:                  '='.
not equals symbol:              '<>'.
less than symbol:               '<'.
less than or equals symbol:     '<='.
greater than or equals symbol:  '>='.
greater than symbol:            '>'.
left paren symbol:              '('.
right paren symbol:             ')'.
left bracket symbol:            '['.
right bracket symbol:           ']'.
dotdot symbol:                  '..'.
stop symbol:                    '@'.

and symbol:                     'AND'.
div symbol:                     'DIV'.
in symbol:                      'IN'.
mod symbol:                     'MOD'.
not symbol:                     'NOT'.
or symbol:                      'OR'.