How to tell whether a character is a letter-like form

Question

Is there any way to programmatically tell whether a given character is a letter or letter-like form (see this reference page for what I mean)?

One idea I had was to use FrontEnd`UndocumentedTestFEParserPacket, to test whether the syntax parser would split the string (i.e. test whether char <> "a" is split), which seems to work. But I am looking for a more provably correct and less undocumented solution if at all possible.

Another idea was to simply check the reference page for a given character/preprocess the full list given above to build a "database" by hand, but it feels like there could be a more straightforward way, hence this question.

Answer 1

Hm. Searching for every command involving Letter with *`*Letter*, I found System`Convert`MLStringDataDump`LetterLikeQ. If s is a String, it applies System`Convert`MLStringDataDump`LetterLikeAuxQ to Characters[s] and wraps it with And@@, so it seems to check if a string is entirely composed of letter like characters. Actually, the whole context System`Convert`MLStringDataDump seems to be interesting for you.

Answer 2

Reading the documentation of Symbol, the following should work:

LetterLikeQ[char_] := Module[
  {ret},
  Begin["`llq`"];
  ret = Quiet@Check[Remove@Evaluate@Symbol@char; True, False];
  End[];
  ret
]

Some examples:

LetterLikeQ["a"]
(* True *)

LetterLikeQ["•"]
(* True *)

LetterLikeQ["\[Rule]"]
(* False *)