What characters are allowed in function names etc?

Question

As the title says, which characters are allowed in identifiers (function, variable, and record field names)? aöø all seem to be fine, as do '_9 if not the first character. <$;% do not. Is it documented somewhere which ranges/blocks of unicode characters and symbols are allowed?

Follow-up question: which characters are allowed in infix operators?

Answer 1

So, after reading the Haskell specs (which can be assumed has influenced Elm), the JavaScript specs, and trial and error, I have arrived at the following rules:

• An identifier must begin with a character from the unicode categories:
  • Uppercase letter (Lu) (modules, types)
  • Lowercase letter (Ll) (functions, variables)
  • Titlecase letter (Lt) (modules, types)
• The rest of the characters must belong to any of the following categories:
  • Uppercase letter (Lu)
  • Lowercase letter (Ll)
  • Titlecase letter (Lt)
  • Modifier letter (Lm)
  • Other letter (Lo)
  • Decimal digit number (Nd)
  • Letter number (Nl)
  • Or be _ (except for in module names).

Technically "Other number" (No) seems to also be valid in Elm, but it crashes after it's been compiled to JavaScript.

I used this tool to get the ranges for each category.