Extending Grammars and InheritanceΒΆ
warning: | Unfinished |
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Another feature taken from OMeta is grammar inheritance. We can
write a grammar with rules that override ones in a parent. If we load
the grammar from our calculator tutorial as Calc
, we can extend it
with some constants:
from parsley import makeGrammar
import math
import calc
calcGrammarEx = """
value = super | constant
constant = 'pi' -> math.pi
| 'e' -> math.e
"""
CalcEx = makeGrammar(calcGrammar, {"math": math}, extends=calc.Calc)
Invoking the rule super
calls the rule value
in Calc. If it
fails to match, our new value
rule attempts to match a constant
name.