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Comment by SupremumLimit | Hacker News Reader

You could do it by separating the body with a semicolon:

    if something_is_true(); log("warning!")

I haven't really considered the preprocessor as I prefer to avoid it as much as possible.

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This doesn't work. "if a; if b; c; d" is then an ambiguous parse to both "if (a) { if (b) { c; d; } }" and "if (a) { if (b) { c; } d; }". If you decide to parse one way, how do you write the other one in a single line?

I'd make this parse as "if (a) { if (b) { c; d; } }" and leave it at that. One of the reasons for significant indentation is to discourage this kind of code layout because it's hard to read.

Okay, concretely, I'd like to see a translation of this real-world C++ code (taken from V8):

  #define RETURN_OBJECT_UNLESS_EXCEPTION(ISOLATE, RETURN_VALUE, RETURN_EMPTY) \
    if (!__allocation__.IsRetry()) {                                          \
      __object__ = __allocation__.ToObjectChecked();                          \
      if (__object__ == (ISOLATE)->heap()->exception()) { RETURN_EMPTY; }     \
      RETURN_VALUE;                                                           \
    }

This seems to be missing backslashes. I haven't considered how to deal with preprocessor macros, but the if statement converts very simply:

    if !__allocation__.IsRetry()
        __object__ = __allocation__.ToObjectChecked()
        if __object__ == (ISOLATE)->heap()->exception(); RETURN_EMPTY
        RETURN_VALUE

This isn't ambiguous like the example you suggested before.

That doesn't work, because if statement is inside preprocessor macro and must be in a single line.

I see what you mean. Yes, the if in a macro is a problem. I haven't addressed macros, that's a whole different can of worms.

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