from the root of the project run
stack build
stack exec interpreter <path-to-program-file>I've provided a couple of program files in the source of the project that demonstrate the interpreters capabilities. (They end with a .hit extension)
yay done.
prompting the user for input is done using the 'prompt' function.
At the start of execution of every 'exec' function (Except Seq, Try and Pass) the 'prompt' function is called. the function will print the statement about to be executed and wait for user input.
a user may inspect the current state of the variable by typing i when prompted the inspect function will then pattern match the current enviroment from the head of the list of states and ookup the name entered.
if name is not found it will return 'error'
in order to record history we must record the changes that happen to our Environment over time as such. the contents of the State monad has been modified such that it holds a list of tuples. Each tuple containing an Enviroment and the Statement that resulted in this enviroment. [(Env, Statement)]
to preform a lookup across all of the enviroments the list of tuples is extracted to a list of enviroments. from then a partially applied lookup is mapped across the list of enviroments. this will give us back a list of the previous states of the variable which can then be printed
As mentioned in our previous section, our state records a list of envrioments and statements that were executed to get us to that enviromet [(Env, State)]. To step backwards we must augment our current state by removing the head of the list and calling exec with the 'new' state being the tail of our list. This means that that statement is running in the same context (Env) it ran in originally.
A user can call back multiple times each time 1 more entry will be removed from the list.
In order to do static analysis we do an initial pass over the code before the user is allowed to step through.
The initial pass is ceneterd around getting information on the satates of the variables. A modified enviroment is used such that it will record the state of each variable rather than its value. this allows us to see if a variable has been used after being initialised or if it has been used before being initialised. The static analysis phase will notify the user of any errors and warnings is finds when it is finished.