#assert <expression> <message> - generate compiler error with <message> when <expression> evaluates to false. 1

See also:

  1. a flavor of #run, allowing arbitrary code at compile time to run as part of an assertion check.
    “Demo: Base language, compile-time execution.” YouTube, uploaded by Jonathan Blow, Oct 31, 2014, https://youtu.be/UTqZNujQOlA?t=3078 

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