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Re^3: RFC: Inline::Blocks or inline as a keyword?

by RonW (Parson)
on Aug 01, 2018 at 00:01 UTC ( #1219610=note: print w/replies, xml ) Need Help??

in reply to Re^2: RFC: Inline::Blocks or inline as a keyword?
in thread RFC: Inline::Blocks or inline as a keyword?

Despite such vehement discouragement, there's nothing (IMHO) intrinsically wrong with source filtering. It's just requires being very careful when using it. Also, it can make a program it using harder to debug.

Anyway, I can suggest how you might use Keyword::Declare to accomplish your inlining module. Though with a modified syntax.

Although Keyword::Declare will let you redefine sub (and other keywords), it won't do what you want. Instead, I suggest adding another keyword, maybe inlinable to mark a subroutine as suitable for inlining. Your handler for inlinable would save the body of the sub for later use by inline, then return the sub definition without the inlinable keyword.

For inline sub definitions, save the body, then instead of returning the sub definition, use the name to define a new keyword. When perl later encounters the name of the sub, it will be treated as a plug-able keyword. then your handler can inline the routine.

Caveat: Keywords defined by Keyword::Declare are only recognized at the beginning of a statement. If you want to inline in the middle of a statement, you have to enclose the "call" in a do { } block.

There might be a plus side to this caveat. Since you know the inlining will always take place at the start of a statement, you might not have to inline it as a do { } block, but as a plain block. This is because if your inlined code isn't "returning" a value, you shouldn't need the do { } block. But if it does "return" a value and you want that value, the "call" will already be inside a do { } block (as long as it is the last (or only) statement in the do { } block).

Summary: A Keyword::Declare based module may be easier to fully implement, but a source filter version probably will result in a cleaner syntax. The Keyword::API might be able to install keywords that work in the middle of expressions, but is not as easy to use as Keyword::Declare.

Disclaimer: I have not tested any of this. YMMV.

Edited to correct grammer errors.

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