def __getattr__(self, name):
try:
return self._rules[name]
except KeyError:
pass
try:
return self._stubs[name]
except KeyError:
pass
self._stubs[name] = result = P.delay(lambda: self._rules[name], "<%s>", name)
return result
def alt(pegs):
return foldr(either, fail, pegs)
def foldr(f, z, xs):
for x in reversed(xs):
z = f(x, z)
return z
# eg_calc.py example
from operator import *
from parson import delay
_ = delay(lambda: g._)
exp3 = delay(lambda: g.exp3)
exp1 = PrececedenceParser(exp3, [
LeftAssoc(('*'+_, mul), ('//'+_, div), ('/'+_, truediv), ('%'+_, mod)),
RightAssoc(('^'+_, pow)),
])
exps = PrececedenceParser(exp1, [
LeftAssoc(('+'+_, add), ('-'+_, sub)),
])
g = Grammar(r"""
top = _ :exps !/./.
exp3 : '('_ :exps ')'_
from operator import add, sub
from parson import anyone, capture, delay, nest, one_of, one_that
end = ~anyone
def match(p, x): return (p + end)([x])
def an_instance(type_): return one_that(lambda x: isinstance(x, type_))
def capture1(p): return capture(p) >> (lambda x: x[0]) # Ouch
var = capture1(anyone)
## (var + var)(eg)
#. ('+', 2)
calc = delay(lambda:
nest(one_of('+') + calc + calc + end) >> add
| nest(one_of('-') + calc + calc + end) >> sub
| capture1(an_instance(int)))
eg = ['+', 2, 3]
## match(calc, eg)
#. (5,)
eg2 = ['+', ['-', 2, 4], 3]
## match(calc, eg2)
#. (1,)
# Exercise: transforming trees with generic walks
flatten1 = delay(lambda:
nest(one_of('+') + flatten1.star() + end)
def an_instance(type_):
return one_that(lambda x: isinstance(x, type_))
def capture1(p):
return capture(p) >> (lambda x: x[0]) # Ouch
var = capture1(anyone)
## (var + var)(eg)
#. ('+', 2)
calc = delay(lambda: nest(one_of('+') + calc + calc + end) >> add
| nest(one_of('-') + calc + calc + end) >> sub
| capture1(an_instance(int)))
eg = ['+', 2, 3]
## match(calc, eg)
#. (5,)
eg2 = ['+', ['-', 2, 4], 3]
## match(calc, eg2)
#. (1,)
# Exercise: transforming trees with generic walks
flatten1 = delay(lambda: nest(one_of('+') + flatten1.star() + end)
| capture1(an_instance(int)))
def alt(pegs):
return foldr(either, fail, pegs)
def foldr(f, z, xs):
for x in reversed(xs):
z = f(x, z)
return z
# eg_calc.py example
from operator import *
from parson import delay
_ = delay(lambda: g.FNORD)
exp3 = delay(lambda: g.exp3)
exp1 = PrececedenceParser(exp3, [
LeftAssoc(('*'+_, mul), ('//'+_, div), ('/'+_, truediv), ('%'+_, mod)),
RightAssoc(('^'+_, pow)),
])
exps = PrececedenceParser(exp1, [
LeftAssoc(('+'+_, add), ('-'+_, sub)),
])
g = Grammar(r"""
:exps :end.
exp3 : '(' :exps ')'
def RuleRef(name): return delay((lambda: rules[name]), name) grammar = Grammar(g)(**globals())
