The read-eval-print loop (REPL) refers to the CommandLineInterface traditionally used to interact with a LispLanguage system or generally with every ProgrammingLanguage system that allows interactive development:
	1. Read an (s-)expression (see EssExpressions)
	2. Evaluate the expression
	3. Print the result
	4. Profi^H^H^H^H^HLoop

In many members of the LispFamily a rudimentary REPL could be implemented as simple as (LOOP (PRINT (EVAL (READ)))).

See WhyLisp for a simple SchemeLanguage implementation of eval. Also see MetaCircularEvaluator.
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CategoryLanguageFeature