Python S-expression emulation using tuple-like objects.

lisp-like, python, s-expressions
pip install etuples==0.3.9



Tests Coverage Status PyPI

Python S-expression emulation using tuple-like objects.


etuples are like tuples:

>>> from operator import add
>>> from etuples import etuple, etuplize

>>> et = etuple(add, 1, 2)
>>> et
ExpressionTuple((<built-in function add>, 1, 2))

>>> from IPython.lib.pretty import pprint
>>> pprint(et)
e(<function _operator.add(a, b, /)>, 1, 2)

>>> et[0:2]
ExpressionTuple((<built-in function add>, 1))

etuples can also be evaluated:

>>> et.evaled_obj

Evaluated etuples are cached:

>>> et = etuple(add, "a", "b")
>>> et.evaled_obj

>>> et.evaled_obj is et.evaled_obj

Reconstructed etuples and their evaluation results are preserved across tuple operations:

>>> et_new = (et[0],) + et[1:]
>>> et_new is et
>>> et_new.evaled_obj is et.evaled_obj

rator, rands, and apply will return the operator, the operands, and apply the operation to the operands:

>>> from etuples import rator, rands, apply
>>> et = etuple(add, 1, 2)

>>> rator(et)
<built-in function add>

>>> rands(et)
ExpressionTuple((1, 2))

>>> apply(rator(et), rands(et))

rator and rands are multipledispatch functions that can be extended to handle arbitrary objects:

from etuples.core import ExpressionTuple
from import Sequence

class Node:
    def __init__(self, rator, rands):
        self.rator, self.rands = rator, rands

    def __eq__(self, other):
        return self.rator == other.rator and self.rands == other.rands

class Operator:
    def __init__(self, op_name):
        self.op_name = op_name

    def __call__(self, *args):
        return Node(Operator(self.op_name), args)

    def __repr__(self):
        return self.op_name

    def __eq__(self, other):
        return self.op_name == other.op_name

rands.add((Node,), lambda x: x.rands)
rator.add((Node,), lambda x: x.rator)

@apply.register(Operator, (Sequence, ExpressionTuple))
def apply_Operator(rator, rands):
    return Node(rator, rands)
>>> mul_op, add_op = Operator("*"), Operator("+")
>>> mul_node = Node(mul_op, [1, 2])
>>> add_node = Node(add_op, [mul_node, 3])

etuplize will convert non-tuple objects into their corresponding etuple form:

>>> et = etuplize(add_node)
>>> pprint(et)
e(+, e(*, 1, 2), 3)

>>> et.evaled_obj is add_node

etuplize can also do shallow object-to-etuple conversions:

>>> et = etuplize(add_node, shallow=True)
>>> pprint(et)
e(+, <__main__.Node at 0x7f347361a080>, 3)


Using pip:

pip install etuples


First obtain the project source:

git clone

Create a virtual environment and install the development dependencies:

$ pip install -r requirements.txt

Set up pre-commit hooks:

$ pre-commit install --install-hooks

Tests can be run with the provided Makefile:

make check