Add a condp implementation

Author: brandonwillard

kanren/condp.py

@@ -0,0 +1,167 @@
+from itertools import tee
+from typing import Mapping, Optional, Sequence, Tuple, Union
+
+from cons import car, cdr
+from toolz import interleave
+from unification import reify
+from unification.utils import transitive_get as walk
+
+from .core import lall, lconj_seq, ldisj_seq
+
+
+def collect(s: Mapping, f_lists: Optional[Sequence] = None):
+    """A function that produces suggestions (for `condp`) based on the values of
+    partially reified terms.
+
+    This goal takes a list of suggestion function, variable pairs lists and
+    evaluates them at their current, partially reified variable values
+    (i.e. ``f(walk(x, s))`` for pair ``(f, x)``).  Each evaluated function should
+    return ``None``, a string label in a corresponding `condp` clause, or the
+    string ``"use-maybe"``.
+
+    Each list of suggestion functions is evaluated in order, their output is
+    concatenated, and, if the output contains a ``"use-maybe"`` string, the
+    next list of suggestion functions is evaluated.
+
+    Parameters
+    ==========
+    s
+        miniKanren state.
+    f_lists
+        A collection of function + variable pair collections (e.g.
+        ``[[(f0, x0), ...], ..., [(f, x), ...]]``).
+    """
+    if isinstance(f_lists, Sequence):
+        # TODO: Would be cool if this was lazily evaluated, no?
+        # Seems like this whole thing would have to become a generator
+        # function, though.
+        ulos = ()
+        # ((f0, x0), ...), ((f, x), ...)
+        for f_list in f_lists:
+            f, args = car(f_list), cdr(f_list)
+            _ulos = f(*(walk(a, s) for a in args))
+            ulos += _ulos
+            if "use-maybe" not in _ulos:
+                return ulos
+        return ulos
+    else:
+        return ()
+
+
+def condp(global_sugs: Tuple, branches: Union[Sequence, Mapping]):
+    """A goal generator that produces a `conde`-like relation driven by
+    suggestions potentially derived from partial miniKanren state values.
+
+    From [1]_.
+
+    Parameters
+    ==========
+    global_sugs
+        A tuple containing tuples of suggestion functions and their
+        logic variable arguments.  Each suggestion function is evaluated
+        using the reified versions of its corresponding logic variables (i.e.
+        their "projected" values).  Each suggestion function is expected to
+        return a tuple of branch labels corresponding to the keys in
+        `branches`.
+    branches
+        Sequence or mapping of string labels--for each branch in a conde-like
+        goal--to a tuple of goals pairs.
+
+
+    .. [1] Boskin, Benjamin Strahan, Weixi Ma, David Thrane Christiansen, and Daniel
+    P. Friedman, "A Surprisingly Competitive Conditional Operator."
+
+    """
+    if isinstance(branches, Mapping):
+        branches_: Sequence = tuple(branches.items())
+    else:
+        branches_ = branches
+
+    def _condp(s):
+        global_los = collect(s, global_sugs)
+        yield from ldisj_seq(lconj_seq(g) for k, g in branches_ if k in global_los)(s)
+
+    return _condp
+
+
+def collectseq(branch_s: Mapping, f_lists: Optional[Sequence] = None):
+    """A version of `collect` that takes a `dict` of branches-to-states.
+
+    Parameters
+    ==========
+    branch_s
+        Branch labels to miniKanren state/replacements dictionaries.
+    f_lists
+        A collection of function + variable pair collections (e.g.
+        ``[[(f0, x0), ...], ..., [(f, x), ...]]``).
+    """
+    if isinstance(f_lists, Sequence):
+        ulos = ()
+        for f_list in f_lists:
+            f, args = f_list
+            _ulos = f({k: reify(args, s) for k, s in branch_s.items()})
+            ulos += _ulos
+            if "use-maybe" not in _ulos:
+                return ulos
+        return ulos
+    else:
+        return ()
+
+
+def condpseq(branches: Union[Sequence[Sequence], Mapping]):
+    r"""An experimental version of `condp` that passes branch-state-reified
+    maps to branch-specific suggestion functions.
+
+    In other words, each branch-specific suggestion function is passed a `dict`
+    with branch-label keys and the its function arguments are reified against
+    the state resulting from said branch.
+
+    .. note::
+
+        Only previously evaluated branches will show up in these `dict`\s, so
+        branch order will determine the information available to each suggestion
+        function.
+
+    Parameters
+    ==========
+    branches
+        Ordered map or a sequence of sequences mapping string labels--for each
+        branch in a `conde`-like goal--to a tuple starting with a single
+        suggestion function followed by the branch goals.
+
+    """
+    if isinstance(branches, Mapping):
+        branches_: Sequence = tuple(branches.items())
+    else:
+        branches_ = branches
+
+    def _condpseq(s, __bm=branches_):
+        __bm, local_items = tee(__bm)
+
+        # Provide each branch-specific suggestion function a copy of the state
+        # after the preceding branch's goals have been evaluated.
+        def f(items):
+            los = set()
+            branch_s = {}
+            for k, goals_branch_sugs in local_items:
+                # Branch suggestions can be `None` and all branch
+                # goals will be added.
+                branch_sugs = car(goals_branch_sugs)
+                goals = cdr(goals_branch_sugs)
+
+                if branch_sugs:
+                    # We only expect one suggestion function per-branch.
+                    branch_sugs = (branch_sugs,)
+                    los |= set(collectseq(branch_s or {k: s}, branch_sugs))
+
+                if branch_sugs is None or k in los:
+                    # TODO: Refactor!
+                    a, b = tee(lall(*goals)(s))
+                    branch_s[k] = next(a)
+                    yield b
+
+                branch_s.setdefault(k, None)
+
+        yield from interleave(f(local_items))
+
+    return _condpseq

tests/test_condp.py

@@ -0,0 +1,115 @@
+from cons import car, cons
+from cons.core import ConsNull, ConsPair
+from unification import isvar, var
+
+from kanren.condp import condp, condpseq
+from kanren.core import Zzz, conde, eq, run
+from kanren.goals import nullo
+
+
+def test_condp():
+    """Test `condp` using the example from [1]_.
+
+    .. [1] Boskin, Benjamin Strahan, Weixi Ma, David Thrane Christiansen, and Daniel
+    P. Friedman, "A Surprisingly Competitive Conditional Operator."
+
+    """
+
+    def _ls_keys(ls):
+        if isvar(ls):
+            return ("use-maybe",)
+        elif isinstance(ls, ConsNull):
+            return ("BASE",)
+        elif isinstance(ls, ConsPair):
+            return ("KEEP", "SWAP")
+        else:
+            return ()
+
+    def _o_keys(o):
+        if isvar(o):
+            return ("BASE", "KEEP", "SWAP")
+        elif isinstance(o, ConsNull):
+            return ("BASE",)
+        elif isinstance(o, ConsPair):
+            if isvar(car(o)) or "novel" == car(o):
+                return ("KEEP", "SWAP")
+            else:
+                return ("KEEP",)
+        else:
+            return ()
+
+    def swap_somep(ls, o):
+        a, d, res = var(), var(), var()
+        res = condp(
+            ((_ls_keys, ls), (_o_keys, o)),
+            {
+                "BASE": (nullo(ls), nullo(o)),
+                "KEEP": (
+                    eq(cons(a, d), ls),
+                    eq(cons(a, res), o),
+                    Zzz(swap_somep, d, res),
+                ),
+                "SWAP": (
+                    eq(cons(a, d), ls),
+                    eq(cons("novel", res), o),
+                    Zzz(swap_somep, d, res),
+                ),
+            },
+        )
+        return res
+
+    def swap_someo(ls, o):
+        """The original `conde` version."""
+        a, d, res = var(), var(), var()
+        return conde(
+            [nullo(ls), nullo(o)],
+            [eq(cons(a, d), ls), eq(cons(a, res), o), Zzz(swap_someo, d, res)],
+            [eq(cons(a, d), ls), eq(cons("novel", res), o), Zzz(swap_someo, d, res)],
+        )
+
+    q, r = var("q"), var("r")
+
+    condp_res = run(0, [q, r], swap_somep(q, ["novel", r]))
+
+    assert len(condp_res) == 4
+    assert condp_res[0][0][0] == "novel"
+    assert isvar(condp_res[0][0][1])
+    assert isvar(condp_res[0][1])
+
+    assert isvar(condp_res[1][0][0])
+    assert isvar(condp_res[1][0][1])
+    assert isvar(condp_res[1][1])
+
+    assert condp_res[2][0][0] == "novel"
+    assert isvar(condp_res[2][0][1])
+    assert condp_res[2][1] == "novel"
+
+    assert isvar(condp_res[3][0][0])
+    assert isvar(condp_res[3][0][1])
+    assert condp_res[3][1] == "novel"
+
+
+def test_condpseq():
+    def base_sug(a_branches):
+        if a_branches["BRANCH1"] == 1:
+            return ("BRANCH3",)
+        else:
+            return (
+                "BRANCH2",
+                "BRANCH3",
+            )
+
+    def test_rel(a):
+        return condpseq(
+            {
+                "BRANCH1": (None, eq(a, 1)),
+                "BRANCH2": ((base_sug, a), eq(a, 2)),
+                "BRANCH3": (None, eq(a, 3)),
+            }
+        )
+
+    q = var("q")
+
+    res = run(0, [q], test_rel(q))
+
+    assert res == ([1], [3])