Journal of Research in Innovative Teaching - National University

The problem involves dealing with operator precedence. According to the calculator
language grammar, the highest precedence is for parenthesis. Parentheses appear in the last
production of the grammar, as shown in Figure 2. The recall operation, denoted by the letter R, is
of the same high precedence. It makes sense to start by replacing an R with its value from the
calculator memory before we evaluate other parts of the expression. However, an R operator can
only appear after we use an S operator, or a store operator. The S operator stores the value of the
token that is to the left of it into the calculator memory. When an S operator is used in an
expression, we can use an R operator somewhere after it. As one would expect, the grammar is
set as to have multiplication and division with higher precedence than addition and subtraction.
Since the calculator grammar is an LL(1) grammar, associativity of operators goes from left to
right.
The Solution
To implement the simple calculator language interpreter, students had to learn important
programming language concepts. The project involved the implementation of a scanner, a parser,
and an abstract syntax tree. The students had to deliver the project in three weeks. With such a
time constraint, APDT proved to be a practical major success. Students were able to learn the
course objectives and deliver the project deliverables on-time. They learned to use Agile Project
Management techniques that made them adjust quickly and dynamically according to project
progress and time frames. The skills learned and used throughout the use case are skills that
every IT professional needs to master in today's accelerated Internet-time workplace (Romney,
2009). The students do not learn the course subject alone, but the best practices and techniques
used in the industry. Using cutting-edge technologies, such as virtualization, and the latest
teaching methodologies, such as APDT, allows for efficient resource management that results in
increased productivity in less time.
Redefining the Problem
The APDT nature of the use case allowed the students to redefine the problem in hand. The
problem was redefined from “implementing a calculator language interpreter” to “implementing
a scanner, and a parser with an abstract syntax tree that would work together to evaluate an
expression according to the calculator language grammar.” This redefinition identified three
major milestones that can be used to break the problem into three subprojects. A smaller problem
is easier to handle and can, in turn, be subdivided without affecting the other subprojects.
Another key concept students learned and dealt with was the integration of the solution for each
subproject to achieve a viable solution to the main problem at hand. All of these are critical
project management concepts essential in the workplace.
The LL(1) grammar was used to build a parser that returns an AST for the parsed
expression. The AST was used to evaluate the parsed expression. The overall data flow of the
calculator interpreter is shown in Figure 3. An expression goes through the scanner that does the
lexical analysis. The scanner returns tokens to the parser. The parser uses the tokens to create an
AST. The AST is then traversed to get the value of the expression (Lee, 2008).
Putting the Pieces Together
Building and integrating the use case project was simplified by using the virtual labs. Students
were able to have isolated development environments for each sub-project that ensured
modification to one would not affect the others. The virtual labs allowed the students to
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