wiki:CompositionAsDot

Version 1 (modified by john@…, 8 years ago) (diff)

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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.

Proposal

Reserve . for use as a qualifier in names. Do not permit . as an operator symbol. (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.
  • We need to make a special case of .. in the [m .. n] case.