I am reading "Revised^5 Report on the Algorithmic Language Scheme," "1.3.1. Primitive, library, and optional features."

In particular, implementations must support portable code by providing a syntactic mode that preempts no lexical conventions of this report.

I don't understand this passage. Maybe it's because English is not my native language. My dictionary does not offer a meaning of the verb "preempt" that makes the passage meaningful. A little clarification would be appreciated.

1 Answer 1


What they're saying is that a conforming implementation must provide a syntactic mode that complies exactly with the lexical conventions of the report. It may ALSO provide ways to change the conventions, but it is absolutely positively required to provide a "plain Vanilla" "just like the Report" mode.

"Preempting a lexical convention" means doing something different. When they say "preempt no conventions", they mean it must not do anything different.

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