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Chapter 2
Interactive Environment

## 2.1 Introduction

DrScheme provides an interactive environment. The upper, or Definitions, window is a full-featured, graphical editor with Emacs-like key bindings. The editor supports on-the-fly syntax coloring that respects the rules of Scheme syntax (and is therefore accurate in a way many other syntax coloring systems are not).

The lower, or Interactions, window implements a read-eval-print loop (R E P L).

The Run button loads the contents of the Definitions window into the Interactions window.

## 2.2 The Transparent REPL

The R E P L in DrScheme is transparent (as described in the DrScheme paper). This avoids subtle history-induced errors and misunderstandings. DrScheme's R E P L avoids these problems in two ways:

- Every time the user clicks Run, DrScheme erases all internal state associated with the R E P L.

- DrScheme warns users when they make changes, do not click Run, and evaluate expressions in the R E P L.

## 2.3 Tabbed Editing

The DrScheme editor lets you edit multiple files in separate tabs, rather than having to edit each file in its own window. The menu entry File | New Tab creates a new tab, and File | Close Tab closes one (if more than one is present).