How LISP's REPL Transformed Human-Computer Interaction in the 1960s

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The Read-Eval-Print Loop (REPL) originated from LISP in the 1960s, developed by AI researchers at MIT who needed to test expressions interactively rather than submit entire programs via batch processing. Before REPL, programmers wrote code on punch cards, submitted them to operators, and waited hours or days to see results and discover bugs. REPL compressed that feedback cycle from days to seconds by reading input, evaluating it, printing the result, and looping back for the next command. The term 'read-eval-print loop' was formally documented in the MACLISP Reference Manual by David Moon in 1974. The concept later became foundational to Python's >>> prompt, Node.js console, Jupyter Notebooks, and browser developer tools, fundamentally shifting programming from batch commands to interactive conversation.

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