Add back middle-dot as function composition for backward compatibility

[kenta2]

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 369041e 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]

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]

See #601, for reference.

[kenta2]

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]

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?