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What Is the Difference Between a Block, a Proc, and a Lambda in Ruby? (2013)
Adam Waxman's Blog
Plain old english: Similar to a suitcase, it's a group of code that when opened (i.e. called), contains whatever was in it when you packed it (i.e. created it). Lambda calculus helps make computable functions easier to study by simplifying its semantics. In different languages these may be called functions, routines, methods, or the generic term callable units.
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