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Bluespec Compiler (BSC)
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Add back middle-dot as function composition for backward compatibility #737

Open kenta2 opened 1 week ago

kenta2 commented 1 week ago

I've encountered legacy code that uses middle-dot as function composition (someone had created a forked version of some of the BSC standard libraries), and it would be nice to still be able to compile that without too much trouble.

This commit https://github.com/B-Lang-org/bsc/commit/369041ec1f347a4ecf44736e54598d3852f11151 changed all instances of middle-dot (U+B7) to ring-operator (U+2218). But we didn't have to stop supporting middle-dot; we can support both middle-dot and ring-operator both for function composition.

(iconv can handle converting from ISO 8859-1 to UTF-8.)

krame505 commented 1 week ago

Can we support this without changing back to ISO 8859-1? I recall prior to this change, editing Prelude.bs was rather annoying. My editor insisted on changing the file encoding whenever I saved, which caused any appearance of U+B7 to get corrupted.

krame505 commented 1 week ago

See https://github.com/B-Lang-org/bsc/pull/601, for reference.

kenta2 commented 1 week ago

Yes, we can support this without changing back to ISO 8859-1. The middle dot exists in unicode, and can be encoded in UTF-8.

quark17 commented 1 day ago

What about adding a flag to BSC to specify additional "prelude" libraries, that are automatically imported. Then you could define the middle-dot compose operator in a file MyPrelude.bs and not have to edit any source files to add an explicit import of MyPrelude (or Utils if you prefer).

BSC already has a hidden flag -use-prelude that controls whether the prelude libraries are implicitly imported or not; the flag is on by default and is used as -no-use-prelude during the compile of BSC's prelude, to avoid a recursive import. We could add a flag like -prelude <packages> and support the + symbol to indicate the default packages (like we do with paths to specify the default path), so a user could add a package with +:MyPrelude and could omit the prelude using an empty list.

Would that satisfy your need to support an old codebase without having to make manual edits to many files?