This isn't an issue for the string binaryFuns as used in the examples, but their lambda variants fail:

---
void main()
{
    import std.algorithm;

    auto w = [[0], [1], [2]];
    assert(w.splitter!"a.front == b"(1).equal([[[0]], [[2]]]));
    
    assert(w.splitter!((a, b) => a.front == b)(1).equal([[[0]], [[2]]])); // fails
}
---

---
onlineapp.d(8): Error: template std.algorithm.iteration.splitter cannot deduce function from argument types !((a, b) => a.front == b)(int[][], int), candidates are:
/dlang/dmd/linux/bin64/../../src/phobos/std/algorithm/iteration.d(3695):        std.algorithm.iteration.splitter(alias pred = "a == b", Range, Separator)(Range r, Separator s) if (is(typeof(binaryFun!pred(r.front, s)) : bool) && (hasSlicing!Range && hasLength!Range || isNarrowString!Range))
/dlang/dmd/linux/bin64/../../src/phobos/std/algorithm/iteration.d(4000):        std.algorithm.iteration.splitter(alias pred = "a == b", Range, Separator)(Range r, Separator s) if (is(typeof(binaryFun!pred(r.front, s.front)) : bool) && (hasSlicing!Range || isNarrowString!Range) && isForwardRange!Separator && (hasLength!Separator || isNarrowString!Separator))
/dlang/dmd/linux/bin64/../../src/phobos/std/algorithm/iteration.d(4264):        std.algorithm.iteration.splitter(alias isTerminator, Range)(Range input) if (isForwardRange!Range && is(typeof(unaryFun!isTerminator(input.front))))
/dlang/dmd/linux/bin64/../../src/phobos/std/algorithm/iteration.d(4510):        std.algorithm.iteration.splitter(C)(C[] s) if (isSomeChar!C)
----


---
void main()
{
    import std.algorithm;
    import std.ascii : toLower;

    assert("abXcdxef".splitter!"a.toLower == b"('x').equal(["ab", "cd", "ef"]));
    assert("abXcdxef".splitter!((a, b) => a.toLower == b)('x').equal(["ab", "cd", "ef"]));
}
---


---
/dlang/dmd/linux/bin64/../../src/phobos/std/algorithm/iteration.d(3726): Error: static function onlineapp.main.splitter!((a, b) => a.toLower == b, string, char).splitter.Result.lastIndexOf cannot access frame of function D main
/dlang/dmd/linux/bin64/../../src/phobos/std/algorithm/iteration.d(3764): Error: function onlineapp.main.splitter!((a, b) => a.toLower == b, string, char).splitter.Result.front cannot access frame of function D main
onlineapp.d(8): Error: template instance onlineapp.main.splitter!((a, b) => a.toLower == b, string, char) error instantiating
---