You should be able to do sbt run to run an initial version of the calculator
interpreter. You should also be able to do sbt test to run some auto-generated
tests of the initial parser and interpreter.
You should be able to do sbt eclipse to generate a ScalaIDE project. Then, you
can import the project in the usual way. Once in ScalaIDE, you can run the
interpreter by opening the file src/main/scala/calculator/calc.scala and
running it.
Running tests in ScalaIDE: The ScalaCheck testing library
doesn't seem to work well with Eclipse yet. You'll probably want to run the
tests outside of Eclipse, using sbt.
Extend the code to implement the following grammar:
n ∈ 𝒵
e ∈ Expr ::= e + t | e - t | t
t ∈ Term ::= t * f | t / f | f
f ∈ Fact ::= n | ( e )
It's best to add features in the following order:
- subtraction
- multiplication
- division
- parenthetical expressions
When you add a new feature to a language, extend the implemention in the following order:
- Intermediate representation
- Data structures
- Sugar (if you want)
- Parser
- Tests
- Implementation
- Semantics
- Tests
- Implementation
If you finish (or just want to explore things more), here are some options.
Can you give better error-checking and error messages for the parser? For the read-eval-print loop? You could also write one or more semantic checks: a pass over the AST to check for errors, e.g., divide by literal 0.
You could add more features to the language, including
- comparisons, e.g.,
<,>,=, etc. - constants, e.g., built-in names such as
πore - variables: assignment and use
- functions (either with or without recursion)