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Comment by perfunctory | Hacker News Reader

This snippet doesn't look right

  macro nullthrows(sourceCodeSnippet) {
    return code`
      const result = ${sourceCodeSnippet}; 
      if (result === null || result === undefined) {
        return result
      } else {
        throw new Error("Uh oh, this returned null:" + "${sourceCodeSnippet}");
    `;
  }

The first and the second occurrences of ${sourceCodeSnippet} look the same so I suppose it will just be evaluated twice. You don't want to evaluate the second occurrence, right? The lisp version doesn't have this problem.

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In this snippet parentheses are in the wrong place

  (defmacro nil-throws [form]
    `(let [result# ~form] ;; assign the evaluation of form to result#
        (if (nil? result#)
          (throw
            (ex-info "uh oh, we got nil!" {:form '~form}) ;; save form for inspection
          result#))))

I guess, should be

  (defmacro nil-throws [form]
    `(let [result# ~form] ;; assign the evaluation of form to result#
        (if (nil? result#)
          (throw
            (ex-info "uh oh, we got nil!" {:form '~form})) ;; save form for inspection
          result#)))

Great catch! Updated, thank you :)

I think it's fine.

In the first occurrence, $(sourceCodeSnippet) is replaced in the code, and later evaluated (and the result of this evaluation will be passed to the const result).

In the second occurrence, it is replaced inside a string, so it doesn't get evaluated, but the source code is just treated as a string (and displayed in the error message).

Note that the macro nullthrows is just generating some code depending of sourceCodeSnippet, and this code will be evaluated later.

Since this is a pseudo code it's hard to tell what the intended semantics are, but if as you say "the source code is just treated as a string", then it's still not right. What if sourceCodeSnippet contains double quotes? OP conveniently uses single quotes in their example

  getUser(db, ‘billy’)

The whole point of lisp macros is that code is not treated as a string.

Hi perfunctory, thanks for the thoughtful read : ).

I'll update that snippet to include something like a `stringify` function, to make the intent more clear.

In terms of the intended semantics: - In some ways my intent was to show these limitations: unless we get code as data structures, our macros would be very brittle.

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