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Fixed formatting
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dabeaz committed May 29, 2013
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206 changes: 103 additions & 103 deletions README.md
Original file line number Diff line number Diff line change
Expand Up @@ -141,109 +141,109 @@ Example
Here is a simple example showing a PLY implementation of a calculator
with variables.

# -----------------------------------------------------------------------------
# calc.py
#
# A simple calculator with variables.
# -----------------------------------------------------------------------------

tokens = (
'NAME','NUMBER',
'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
'LPAREN','RPAREN',
)

# Tokens

t_PLUS = r'\+'
t_MINUS = r'-'
t_TIMES = r'\*'
t_DIVIDE = r'/'
t_EQUALS = r'='
t_LPAREN = r'\('
t_RPAREN = r'\)'
t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'

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

# Ignored characters
t_ignore = " \t"

def t_newline(t):
r'\n+'
t.lexer.lineno += t.value.count("\n")
def t_error(t):
print("Illegal character '%s'" % t.value[0])
t.lexer.skip(1)
# Build the lexer
import ply.lex as lex
lex.lex()

# Precedence rules for the arithmetic operators
precedence = (
('left','PLUS','MINUS'),
('left','TIMES','DIVIDE'),
('right','UMINUS'),
)

# dictionary of names (for storing variables)
names = { }

def p_statement_assign(p):
'statement : NAME EQUALS expression'
names[p[1]] = p[3]

def p_statement_expr(p):
'statement : expression'
print(p[1])

def p_expression_binop(p):
'''expression : expression PLUS expression
| expression MINUS expression
| expression TIMES expression
| expression DIVIDE expression'''
if p[2] == '+' : p[0] = p[1] + p[3]
elif p[2] == '-': p[0] = p[1] - p[3]
elif p[2] == '*': p[0] = p[1] * p[3]
elif p[2] == '/': p[0] = p[1] / p[3]

def p_expression_uminus(p):
'expression : MINUS expression %prec UMINUS'
p[0] = -p[2]

def p_expression_group(p):
'expression : LPAREN expression RPAREN'
p[0] = p[2]

def p_expression_number(p):
'expression : NUMBER'
p[0] = p[1]

def p_expression_name(p):
'expression : NAME'
try:
p[0] = names[p[1]]
except LookupError:
print("Undefined name '%s'" % p[1])
p[0] = 0

def p_error(p):
print("Syntax error at '%s'" % p.value)

import ply.yacc as yacc
yacc.yacc()

while 1:
try:
s = raw_input('calc > ') # use input() on Python 3
except EOFError:
break
yacc.parse(s)
# -----------------------------------------------------------------------------
# calc.py
#
# A simple calculator with variables.
# -----------------------------------------------------------------------------

tokens = (
'NAME','NUMBER',
'PLUS','MINUS','TIMES','DIVIDE','EQUALS',
'LPAREN','RPAREN',
)

# Tokens

t_PLUS = r'\+'
t_MINUS = r'-'
t_TIMES = r'\*'
t_DIVIDE = r'/'
t_EQUALS = r'='
t_LPAREN = r'\('
t_RPAREN = r'\)'
t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'

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

# Ignored characters
t_ignore = " \t"

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

def t_error(t):
print("Illegal character '%s'" % t.value[0])
t.lexer.skip(1)

# Build the lexer
import ply.lex as lex
lex.lex()

# Precedence rules for the arithmetic operators
precedence = (
('left','PLUS','MINUS'),
('left','TIMES','DIVIDE'),
('right','UMINUS'),
)

# dictionary of names (for storing variables)
names = { }

def p_statement_assign(p):
'statement : NAME EQUALS expression'
names[p[1]] = p[3]

def p_statement_expr(p):
'statement : expression'
print(p[1])

def p_expression_binop(p):
'''expression : expression PLUS expression
| expression MINUS expression
| expression TIMES expression
| expression DIVIDE expression'''
if p[2] == '+' : p[0] = p[1] + p[3]
elif p[2] == '-': p[0] = p[1] - p[3]
elif p[2] == '*': p[0] = p[1] * p[3]
elif p[2] == '/': p[0] = p[1] / p[3]

def p_expression_uminus(p):
'expression : MINUS expression %prec UMINUS'
p[0] = -p[2]

def p_expression_group(p):
'expression : LPAREN expression RPAREN'
p[0] = p[2]

def p_expression_number(p):
'expression : NUMBER'
p[0] = p[1]

def p_expression_name(p):
'expression : NAME'
try:
p[0] = names[p[1]]
except LookupError:
print("Undefined name '%s'" % p[1])
p[0] = 0

def p_error(p):
print("Syntax error at '%s'" % p.value)

import ply.yacc as yacc
yacc.yacc()

while 1:
try:
s = raw_input('calc > ') # use input() on Python 3
except EOFError:
break
yacc.parse(s)


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