lexer.py

import ply.lex as lex

num_errors = 0

reserved = {
  'and'   : 'AND',
  'do'    : 'DO',
  'else'  : 'ELSE',
  'while' : 'WHILE',
  'then'  : 'THEN',
  'end'   : 'END',
  'if'    : 'IF',
  'var'   : 'VAR',
  'or'    : 'OR',
  'not'   : 'NOT'
}

# List of token names
tokens = [
  'ID', 'NUMBER', 'PLUS', 'MINUS', 'TIMES', 'DIVIDE',
  'EQUAL', 'NOTEQUAL', 'LESSEQUAL', 'GREATEREQUAL',
  'LESS', 'GREATER', 'ASSIGN', 'LPAREN', 'RPAREN',
  'SEMICOLON', 'COMMA'
] + list(reserved.values())

t_PLUS          = r'\+'
t_MINUS         = r'-'
t_TIMES         = r'\*'
t_DIVIDE        = r'/'
t_EQUAL         = r'=='
t_NOTEQUAL      = r'~='
t_LESSEQUAL     = r'<='
t_GREATEREQUAL  = r'>='
t_LESS          = r'<'
t_GREATER       = r'>'
t_ASSIGN        = r'='
t_LPAREN        = r'\('
t_RPAREN        = r'\)'
t_SEMICOLON     = r';'
t_COMMA         = r','

# Regular expressions rules
def t_ID(t):
  r'[a-zA-Z_][a-zA-Z_0-9]*'
  t.type = reserved.get(t.value, 'ID')
  return t

def t_NUMBER(t):
  r'\d+'
  t.value = int(t.value)
  return t

t_ignore = ' \t'

def t_newline(t):
  r'\n+'
  t.lexer.lineno += len(t.value)

def t_error(t):
  global num_errors
  print "Ilegal character '%s' at line: %d" % (t.value[0], t.lexer.lineno)
  num_errors += 1
  t.lexer.skip(1)

# Building lexer
lexer = lex.lex()