structs can have an impact on learnability. Empirical studies by Stefik and Seibert34 have found that common keywords like for or operators such as != serve as hard-to-learn jargon, and are not as easily learnable as familiar words such as repeat or unequal. They found the syntax of languages such as Java and Perl are no more learnable than a synthetic programming language with randomly selected punctuation used for keywords. Even more important for learnability are the abstractions chosen by language designers to allow users to build simple programs with compelling behavior. For example, the designers of Alice worked with users to develop intuitive abstractions for controlling 3D animations. During their design process, the Alice team eliminated jargon such as transformation matrices and substituted more intuitive concepts like object-relative motions. These new abstractions made it easier for users to specify 3D animations. 7

Designing languages and libraries focused on learnability based on empirical evidence is a major area for future work.

Runtime understanding. The dynamic state of a program can be made more understandable by making its state visible. For example, Code.org highlights the individual block actively running so the correspondence between code and action can be seen. Snap! provides widgets for every variable to show the current state.

Even with highly visible state, understanding actions in the past or future can be difficult. Liveness20 is one approach to addressing this problem. A live system aims to make actions concrete by applying them immediately to the current state. For example, in App Inventor, Scratch, and Snap!, many edits to a running block program take effect immediately, without the need to restart the program.

Another approach for making the
evolution of state understandable is to
allow the programmer to travel in time
by inspecting, advancing or rewinding
the timeline of a program. The concept
of omniscient debugging was first de-
scribed in the early 1970s as a capabil-
ity to trace backward in time through
execution history to identify the loca-
Directly manipulable blocks also
encourage bottom-up tinkering with
program pieces in ways not directly sup-
ported by raw text. Blocks programmers
experiment with blocks by connecting
them to build islands of code fragments
on the programming surface that are
isolated from the main program. 22, 38 In
blocks environments supporting live-
ness, 20 these fragments can be executed
by pointing and clicking, providing a key
benefit of interpreted text-based lan-
guages without a read-eval-print
loop console separate from the editor.
The program gradually grows as it is aug-
mented by dropping in these fragments
when they behave as desired.

Learnability Beyond Blocks. Blocks aid in the construction of code, but blocks alone are not enough to make a programming language learnable. Users new to a language face additional learning challenges:

˲ They must wrestle with practical aspects like installing language tools, saving/loading programs, and so on;

˲ They must learn the vocabulary of the language and understand the concepts denoted by its words;

˲ They need to understand runtime semantics such as flow of control and changes in state over time; and,

˲ They eventually need to learn common patterns of use, moving beyond isolated concepts.

Each of these learning hurdles can be helped or hindered by the programming environment, and each of these problems is an area of active research and development.

Programming online. To simplify installation, programming tools are moving online. When a programming environment is in a Web browser, a new programmer is just a few clicks away from creating a first program. A cloud-based programming tool can provide a complete and consistent programming environment with fewer potential problems.

Although blocks programming environments for beginners have long been offered online, text-based programming environments are also becoming available online. With tools such as Cloud 9, CodeAnywhere, and CodeEnvy, programmers of all levels can benefit from working online.

Words, concepts, and abstractions.

The names chosen for language con-

By organizing code
as visible chunks,
blocks help new
programmers
concentrate on
what the code
means rather than
the notation that is
used to write it.