(REPL) refers to the Command Line Interface traditionally used to interact with a Lisp Language system or generally with every Programming Language system that allows interactive development.
Read an (s-)expression (see Ess Expressions)
Evaluate the expression
Print the result
Profi^H^H^H^H^HLoop
In many members of the Lisp Family a rudimentary REPL could be implemented as simple as (LOOP (PRINT (EVAL (READ)))).
See Why Lisp for a simple Scheme Language implementation of eval. Also see Meta Circular Evaluator.
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