Tuesday, December 26, 2017

code for Wombat/Marsupial Operators

[Update: This was an insanely premature announcement. Stay tuned ...]
[Update2: now looks roughly ok -- next step write an interpreter]

One of Wombat's many aims was to have user-defined operators that are so good that there is no need for operators to be built into the language at all.

  • Parentheses ("(...)") are just an operator with no left and no right that maps to the identity function.
  • Semicolon ("statement1;statement2;expression") is an operator: with left and right and low priority on both sides.
  • etc -- operators are the only syntax for most users.
We now support different versions of an operator with a left or with no left (e.g. x-y versus -z). Also operators overlap as long as they stay the same until they diverge by either a (mandatory) operator or by whether a mandatory operator is/isn't followed by an operand. E.g. "[" has 3 forms:
  • [ ] is the empty list
  • [ space-separated-elements ] is an ordinary list. Note that wombat uses space as a separator here, so procedure calls have to use adjacency f(x) or be parenthesised (f x). You don't like that? It's really trivial to change operators, and still be compatible with other code.
  • [ head | tail ] intended for pattern matching, but works either way.
The point is that both the compiler and the reader can understand which is which with only one token lookahead.

The code for this now passes the barest one line test. I'll get back to testing it when I have more wombat code. The code is in v0.0.1 under marsupial (https://github.com/rks987/marsupial/tree/v0.0.1). Marsupial is just the bare minimum, and the plan is eventually to separate out the include/import/require files that turn marsupial into wombat.

If any languages out there would like a comprehensive scheme for user defined operators then I might find time to help. It is written in python3, but really just uses json-level features (apart from using generators), so I think it will fit into other languages. The problem is interacting with compiler defined operators already there. Wombat doesn't have that problem because there aren't any!

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