transparent lambda

Mark Mahieu markmahieu at
Mon Dec 28 12:30:10 PST 2009

On 28 Dec 2009, at 20:18, Neal Gafter wrote:

> On Mon, Dec 28, 2009 at 12:09 PM, Mark Mahieu <markmahieu at> wrote:
> Hmm.  Wouldn't it only *break* TCP if it were also valid in a nested lambda but with a different semantic meaning, or if there were no corresponding form for when the statement is wrapped in a lambda?
> I'd say "syntax error" is a pretty serious breakage.  To put it another way, the correspondence principle applied to lambda expressions says the meaning of a (nested) expression should not change when wrapped in a lambda.  Changing the meaning from "allowed" to "not allowed" is therefore not transparent.
> Any expression form that has subexpressions should be capable of being nested.
> Cheers,
> Neal

I see - that certainly clears things up.  I should probably revisit Tennent's text with a stricter interpretation of 'equivalent', 'analogous mechanism' etc :)

Thanks for your patience.


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