A Python example that uses miniKanren to substitute elements in a list/graph structure.

kanren-substitution-example.py

from unification import var
from kanren import run, eq

# Logical conjunction
from kanren import lall as lconj

# Logical disjunction
from kanren import lany as ldisj

# `conde((a, b), (c, d), ...)` == `ldisj(lconj(a, b), lconj(c, d), ...)`

from symbolic_pymc.relations.graph import graph_applyo


def replace_oneo(in_obj, out_lv):
    g = lconj(eq(in_obj, 1),
              eq(out_lv, "one"))
    return g


def replace_twoo(in_obj, out_lv):
    g = lconj(eq(in_obj, 2),
              eq(out_lv, "two"))
    return g


def number_to_wordo(in_obj, out_lv):
    res = ldisj(replace_oneo(in_obj, out_lv),
                replace_twoo(in_obj, out_lv))
    return res


def numbers_to_words(in_obj):
    """Replace 1 with "one"."""
    out_lv = var('output')

    # Try returning all results by setting 1 -> 0; it should be
    # slower for the nested lists!
    res = run(1, out_lv,
              graph_applyo(number_to_wordo, in_obj, out_lv))
    return res


numbers_to_words(1)
numbers_to_words(2)

numbers_to_words([1])
numbers_to_words([2])

numbers_to_words([1, 2])

numbers_to_words([1, [1, 2]])
numbers_to_words([1, [1, [1, 2]]])