67 lines
1.7 KiB
Python
67 lines
1.7 KiB
Python
"""
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Generic AST transformation classes.
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.. autosummary::
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:toctree: transform
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comparison
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observation
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specials
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"""
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class Transformer:
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"""
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Base class for AST transformers.
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"""
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def transform(self, ast):
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"""
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Transform the given AST and return the resulting AST.
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:param ast: The AST to transform
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:return: A 2-tuple: the transformed AST and a boolean indicating whether
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the transformation actually changed anything. The change detection
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is useful in situations where a transformation needs to be repeated
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until the AST stops changing.
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"""
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raise NotImplementedError("transform")
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class ChainTransformer(Transformer):
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"""
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A composite transformer which consists of a sequence of sub-transformers.
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Applying this transformer applies all sub-transformers in sequence, as
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a group.
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"""
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def __init__(self, *transformers):
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self.__transformers = transformers
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def transform(self, ast):
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changed = False
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for transformer in self.__transformers:
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ast, this_changed = transformer.transform(ast)
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if this_changed:
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changed = True
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return ast, changed
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class SettleTransformer(Transformer):
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"""
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A transformer that repeatedly performs a transformation until that
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transformation no longer changes the AST. I.e. the AST has "settled".
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"""
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def __init__(self, transform):
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self.__transformer = transform
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def transform(self, ast):
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changed = False
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ast, this_changed = self.__transformer.transform(ast)
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while this_changed:
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changed = True
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ast, this_changed = self.__transformer.transform(ast)
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return ast, changed
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