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On 11/24/2012 07:07 PM, John Cowan wrote:
Per Bothner scripsit:The question is: Do we want there to be a default implementation of ($quasi-value-transformer$:foo ...) as (foo ...)?And what is the default implementation of (foo ...)?
Error.
We seem to be on an infinite regress, and I'd rather just stop at $quasi-value-transformer$:foo. And start there too.
Handly an infinite regress. But I agree the extra complication of defining a default "fall-back" implementation of $quasi-value-transformer$:foo seems marginal. I think it may make sense to define one or more library functions to massage the arguments - for example concatenating the components of the literal part. These would be to make it combine the argument list - or example combining the literal part to a single string-valued expression.
I propose this: (1') The reader returns ($quasi-value-transformer$:foo ...). If it was called from `read`, that's what the program gets. If it was called from a compiler or interpreter, it applies its normal rules to determine if $quasi-value-transformer$:foo is bound, and if not, takes its normal error recovery action, whatever that is.
That seems reasonable. What do you think of ($construct$:foo ..) instead of the rather ungainly ($quasi-value-transformer$:foo ...)?
It is indeed, and (1') has the same advantage.An implementation can then *optionally* provide a default implementation and/or a mechanism to override the default.By the same token, a compiler or interpreter can have some default mechanism that recognizes symbols of this type and provides them with some default value or behavior.
Kawa has a few of these. For example CLASSNAME? becomes an instance test, and NNNUNIT (e.g. 2.5cm) becomes a "quantity" (number-with-unit). An implementation could have some fallback-mechnanism for $construct$:foo, but I agree it doesn't seem worthwhile trying to standardize it. -- --Per Bothner per@xxxxxxxxxxx http://per.bothner.com/