set() can now reference other named token sets #74
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I originally wanted this feature to use new syntax, e.g.
%generate foo = set('a' | 'b');
%generate bar = foo | set('c');
%generate boo = foo & set('c');
so that
* an identifier in set() is always a terminal/nonterminal;
* identifier outside of set is always another named token set.
However, that turned out to be a bigger change than what I was hoping for.
So, this commit allows identifiers in set() to reference both
terminals/nonterminals and other named token sets. Rewriting the above
example,
%generate foo = set('a' | 'b');
%generate bar = set(foo | 'c');
%generate boo = set(bar & 'c');
inspirer
reviewed
Nov 24, 2023
| name := expr.Symbol().Name() | ||
| if index, ok := c.namedSets[name.Text()]; ok { | ||
| if index >= len(c.out.Sets) { | ||
| c.Errorf(expr.TmNode(), "forward references are not allowed") |
Owner
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fwiw Forward references should work just fine - the circular dependencies are handled inside syntax/set.go.
| c.Errorf(expr.TmNode(), "ambigious reference") | ||
| return ret | ||
| } | ||
| return c.out.Sets[index] |
Owner
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This works but what happens here under the hood is that the set expression you reference here is evaluated several times. I'd instead introduce a new syntax.SetOp - Reference, and store the SetIndex inside TokenSet (similar to syntax.Expr.SetIndex). Then inside syntax/set->translate function create a future set.
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I originally wanted this feature to use new syntax, e.g.
so that
However, that turned out to be a bigger change than what I was hoping for. So, this commit allows identifiers in set() to reference both terminals/nonterminals and other named token sets. Rewriting the above example,