empty lambda

ceving

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Oct 30, 2023, 6:06:28 AM10/30/23

to chibi-scheme

Why is it ok to have an empty begin but no empty lambda?

ceving

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Oct 30, 2023, 6:37:29 AM10/30/23

to chibi-scheme

Why I ask: SICP chapter 4 implements begin as a sequence and does not allow empty sequences. But most Schemes allow an empty begin at least at top level.

For example "(begin)" is ok for Chez, but "(display (begin))" is not. Chibi does not care and displays undef.

Why is there so much inconsistency? What is the benefit?

Alex Shinn

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Nov 2, 2023, 2:57:03 AM11/2/23

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We allow empty begins in definition context (not just top-level) for macros which can expand into 0 or more definitions.

Such macros can't output a dummy expression (e.f. #f or unspecified) in such a case because this is not a definition.

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Alex

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