Is any Json string a valid Elm string?


please do not ask why I want to do that, but I’m interested in generating some Elm code from another language. I need to use literal strings in the produced code, and unfortunately I couldn’t find a precise specification of what an Elm string is supposed to look like.
I was thinking of using json strings everywhere a litteral string is needed. Would that produce valid Elm code?

Thanks for your help.

I think you should be fine

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Are you wondering if a valid JSON string literal is also a valid Elm string literal, syntax wise?

If so: They are not.

For example, "\u1234" is a valid JSON string literal, but a syntax error in Elm (the equivalent syntax is "\u{1234}").

You can find the syntax definition for a JSON string literal here: JSON

For Elm, there is no specification, only the source code of the compiler: compiler/String.hs at 047d5026fe6547c842db65f7196fed3f0b4743ee · elm/compiler · GitHub

If your program that generates Elm code is written in JavaScript, you could switch from JSON.stringify(myString) to makeElmString(myString) defined here: node-test-runner/Generate.js at 026581eb144a32defd6dae3c3de5c46e5e987527 · rtfeldman/node-test-runner · GitHub (it should be at least somewhat complete).

Reading through the source code I linked to, I believe the rules are:

  1. A starting double quote ".
  2. Zero or more of:
    • Any character but ", \n and \. (Possibly other newline characters?)
    • Or a valid escape
  3. An ending double quote ".

A valid escape is:

  • A backslash followed by one of n, r, t, ", ', \
  • Or a backslash followed by:
    1. u
    2. {
    3. 4-6 hex characters (0-9, a-z, A-Z), which when treated as a number is at most 0x10FFFF
    4. }

In summary, I think the differences to JSON are:

  • Escape syntax / valid escapes
  • Possibly newline characters
  • Possibly handling of characters 0x00-0xFF

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