Read-Eval-Print

• (current-prompt-read [proc]) gets or sets a procedure that takes no arguments, displays a prompt string, and returns an expression to evaluate. This prompt read handler is called by the read phase of read-eval-print-loop (see section 14.1). The default prompt read handler prints ``> '' and returns the result of (read).
• (current-eval [proc]) gets or sets a procedure that takes an S-expression and returns its value (or values; see Chapter 2). This evaluation handler is called by eval, the default load handler, and read-eval-print-loop to evaluate an expression (see section 14.1). The default evaluation handler compiles and executes the expression in the current namespace (determined by the current-namespace parameter).
• (current-namespace [namespace]) gets or sets a namespace value (see section 9.3) that determines the global variable namespace used to resolve variable references. The current namespace is used by the default evaluation handler, the compile procedure, and other built-in procedures that operate on global variables.
• (current-print [proc]) gets or sets a procedure that takes a value to print. This print handler is called by read-eval-print-loop (see section 14.1) to print the result of an evaluation (and the result is ignored). The default print handler prints the value to the current output port (determined by the current-output-port parameter) and then outputs a newline.