[Grace-core] A little bit of the String library

[Andrew P. Black]

Folks,

While on a train, with a few hours to kill (and electricity!) I started writing a little bit of Grace code — a start at the String library — because I need more example code to test the parser.  My code is attached.

I almost immediately found that I was raising language design questions to which I didn't know the answers.

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I'm defining a "StringTrait" object from which other objects will inherit.  Do we have a way of putting "abstract methods" in an object?  I used the (new) keyword "required" in place of a method body.   Should the whole object be explicitly flagged as abstract in some way, or if this inferred from the existence of required methods?  

|| for String concatenation?

I wanted to use // for integer division.  But we have already taken it to mean "comment".    Switch to "--" for comments?

Can we say

		const (a, b, c) := method that answers a tuple

I think that we have to allow this.  Are the parens necessary?  I think that

		const a, b, c := method that answers a tuple

parses unambiguously, but maybe it's harder to read?

raise <exception object> for raising exceptions?  Or signal?  Or throw (I don't like throw, it makes me think of, well, I would rather not say.)

I wanted an enumeration type TotalComparison = greater | less | equal. I defined it as three objects and a comprises clause.   This is a type issue, which we know that we haven't yet talked about.   Thoughts?

As yet, I haven't put any of these into the grammar.

	Andrew