Class Node

source code

A base class for AST nodes.

It is designed to be applied to a list of results, via >.

Nodes support both simple list--like behaviour:

>>> abc = Node('a', 'b', 'c')
>>> abc[1]
'b'
>>> abc[1:]
['b', 'c']
>>> abc[:-1]
['a', 'b']

and dict--like behaviour through attributes:

>>> fb = Node(('foo', 23), ('bar', 'baz'))
>>> fb.foo
[23]
>>> fb.bar
['baz']

Both mixed together:

>>> fb = Node(('foo', 23), ('bar', 'baz'), 43, 'zap', ('foo', 'again'))
>>> fb[:]
[23, 'baz', 43, 'zap', 'again']
>>> fb.foo
[23, 'again']

Note how ('name', value) pairs have a special meaning in the constructor. This is supported by the creation of "named pairs":

>>> letter = Letter() > 'letter'
>>> digit = Digit() > 'digit'
>>> example = (letter | digit)[:] > Node
>>> n = example.parse('abc123d45e')[0]
>>> n.letter
['a', 'b', 'c', 'd', 'e']
>>> n.digit
['1', '2', '3', '4', '5']

However, a named pair with a Node as a value is coerced into a subclass of Node with the given name (this keeps Nodes connected into a single tree and so simplifies traversal).