Eliminate . as an operator

In early Haskell, . was used as function composition. In later versions of Haskell, it also became used as a name qualifier.

These two uses do not fit well together, leading to special lexical rules (P11 of the report). As a test, before reading the report, can you lex the following: "f.g", "F.g", "F . g", "f..", "F..", and "F.". I couldn't. (See QualifiedIdentifiers for a related problem.)

Proposed syntaxes for RankNTypes and ExistentialQuantification also use . as a special symbol.

Proposal

Reserve . for use as a qualifier in names. Do not permit . as an operator symbol (or as a symbol character?). (Also continue to permit it as a decimal point in floats).

Pros

• Much much simpler. Not impossible to remember.

Cons

• We lose . as composition. Mostly this doesn't matter as $ is probably more common in reality anyway. Perhaps use `o` as infix composition instead if it is really important. Note that `o` is three characters - it would be nicer to use plain o infix, but that would require another special lexical rule.
• We need to make a special case of .. in the [m .. n] case.