** What productivity gains do interactive programming environments provide over
   batch compilers?

A good interactive programming environment puts the full power of
the extension language at your disposal, giving you immediate and
direct access to the functions and data structures that compose the
system.

You can display and modify live data structures, and examine, call,
and redefine functions from the keyboard. You can implement, test,
analyze, and revise modules of code, without writing
stand-alone drivers to test out each module, and without
recompiling and relinking after every change.

** Why use an interactive language rather than a graphical prototyping
   system?

Graphical prototyping systems are generally very good at what they're
designed to do, but aren't applicable outside their narrow domain.

Interactive programming environments are more widely applicable, and
they can be extended to implement interfaces and communication
protocols tailored to the needs of specific applications.  

The NeWS window system and the Emacs text editor provide
programmers with a high level of power and flexibility, to rapidly
prototype, evaluate, and implement unconventional ideas. Much of
the prototype code can be reused in the final system.

Emacs and NeWS are especially useful for creating front ends for
command line driven program. Operating system processes can be run
under the control of Emacs, which can provide them with pre-processed
input, and capture and manipulate their output. With NeWS, a
programmer can use object oriented PostScript to build a graphical
front end to an application that provides local input processing and
feedback, resulting in low client/server network traffic and high
interactive performance.

** How expert must a user interface designer be in programming in general
   to derive productivity gains from an interactive programming environment?

The presence of an extension language in a rapid prototyping system
does not preclude that the system is usable by non-programmers.
Programmers can use the extension language to create a concise,
application specific command language that is easy for
non-programmers to use.

Novice programmers can take advantage of pre-defined commands and
objects, putting them together and customizing building blocks
written by other people.  Experienced programmers can take full
advantage of the power and flexibility of the extension language,
creating their own building blocks, which others can use.

** How expert must a user interface designer be in a specific interactive
   language, to derive productivity gains from using that language?

A language is easier to learn interactively that in a batch
environment. Direct access and immediate feedback gives a programmer
immersed in an interpretive environment intimate experience with the
language, and incentive to experiment.

Using object oriented programming in NeWS, programmers can utilize 
pre-defined classes of objects without knowing about their internals,
and they can make their own custom classes by subclassing already
existing classes. NeWS supports this building block approach very
well. 

Emacs, which runs on dumb terminals as well as window systems,
provides an integrated program development system, with online
documentation, command name completion, and many packages of
specialized editing functions that can be bound to key sequences,
or used in building higher level packages.

** How does one migrate from prototype to product?

At one end of the spectrum, a prototype can be iteratively refined
until it's solid enough to serve as the finished product.  At the
other end, a prototype can be analyzed, written off as a learning
experience, redesigned, and totally reimplemented. 

A prototype can provide a supporting framework on top of which can
be build modules that would be impossible to implement and test in
a vacuum.  Even if parts of the prototype must eventually be
rewritten, independent modules can still be reused.

** How would you prioritize the importance to a user interface
   designer's productivity among: use of an interactive environment,
   the particular language chosen, and pre-existing library or
   component packages?

1) Use of an interactive environment.
   You've got to be able to participate in the environment.

2) The particular language chosen.
   It's got to be an environment worth participating in.

3) Pre-existing library or component packages.
   You need a solid base on top of which to build,
   and some concrete examples of how things are put together.

** Once a user interface designer has elected to use an interactive language,
   how does he select the language?

Different languages are good at talking about different things. 
Figure out what you want to talk about first, and then choose the
language. 

Here are some words used to describe concepts that certain
interactive programming languages are good at manipulating.

NeWS:
	graphics, geometry, transformations, fonts, paths, images,
	colors, lines, curves, regions, input devices, events,
	canvases, processes, synchronization, remote procedure
	calls, classes, objects, windows, menus, scroll bars
Emacs:
	text, strings, characters, words, lines, paragraphs,
	windows, buffers, marks, streams, processes, files,
	directories, databases, abbreviations, keystrokes,
	bindings, macros, regular expressions, syntax
Forth:
	hardware, registers, interrupts, real time control,
	diagnostics, integers, pointers, stacks, words, vocabularies,
	control structuctures, interpreters, assemblers,
	disassemblers, compilers, decompilers, meta compilers