Before starting, explain to yourself how "switch on types" in the method visit of ASTInterpreter.java works ? How to "return" a value from a case ? How to call it, how to do a recursive call ?
We make a recusrive call in the AST expression We use yield to return a value in a case. We call the visit function and we pass down the environnement
The file ASTInterpreterTest contains several unit tests for all the following questions. Now, we want to implement the AST interpreter when there is a constant String (a literal). What is the class of the corresponding node in the AST (you can take a look to the file smalljs.md for a summary). How to implement it ? Is it enough to make test marked Q2 pass ? what other node should be implemented too ?
a Literal
We now want to print something. What is the class of the node in the AST to implement ? For now, we will suppose that the only function is the print function. How to find the function "print" which is registered in the global environment ? How to call it ? Add the code to support the function print and verify that the test marked Q4 pass.
We find the print function with lookup. we call it with "invoke()"
What is the return value of the function print in JavaScript ? Make sure your interpreter behave accordingly and verify that the test marked Q5 pass.
it returns undefined
We now want to support other functions than just print. Where all the builtin functions are defined ? How to modify the code to support all builtin functions ? What is the "qualifier" component represent ? Is the visit of a function call enough to implement the support of a function call ? What is the method in the environment env to look for a value associated to a name ? What is the class that represent a function at runtime ? Modify the code and verify that the test marked Q6 pass.
-- Nothing more, we use the lookup in the environment. The qualifier is what comes before the parenthesis. FunCall
We now want to be able to declare or assign a local variable. What is the class of the node in the AST corresponding to a local variable assignment ? Implement the interpreter part and verify that all the tests marked Q8 pass.
--
LocalVarAssignment