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If you start Guile without specifying a particular program for it to execute, Guile enters its standard Read Evaluate Print Loop — or REPL for short. In this mode, Guile repeatedly reads in the next Scheme expression that the user types, evaluates it, and prints the resulting value.
The REPL is a useful mechanism for exploring the evaluation behaviour
described in the previous subsection. If you type string-append,
for example, the REPL replies #<primitive-procedure
string-append>, illustrating the relationship between the variable
string-append and the procedure value stored in that variable.
In this manual, the notation ⇒ is used to mean “evaluates to”. Wherever you see an example of the form
expression ⇒ result
feel free to try it out yourself by typing expression into the REPL and checking that it gives the expected result.