Assignment - Parsers and State

Part 1: Imp Parser

In this first part, you will complete the parser for the Imp language. Most of the parser has already been implemented.

TODO:
Implement the cWhileP parser. The while command has the following syntax (EBNF):

cWhile = "while" boolExpr "do" cseq "endwhile"

Example:

q := 0;
r := m;
while (n <= r) do
  q := (q + 1);
  r := (r - n)
endwhile

In Main.hs, you can find the code that loads the content of a file, runs the parser and prints the output. Its main looks as follows:

main :: IO ()
main = do
    [fileName] <- getArgs
    content <- readFile fileName
    putStrLn "Parsed file:"
    print $ parseImp content

To run the above code on a test file, execute the following command:
cabal run imp Lang/Test/intDiv.iml
To run the parser tests, execute the following command:
cabal test imp-test --test-show-details=direct --test-option=--match --test-option="4. Parser".

Hints:

Get inspiration from the if command parser.
You may want to add more tests to the parseSpec in Tests.hs to ensure that your implementation works correctly.

Part 2: Syntactic Sugar

Currently, our Imp language is somewhat limited. In this part, you will add syntactic sugar to the language. Our Expr type only supports the relational operators = and less-than <. The <= operator is only available in the front end and desugared by the parser as follows: a <= b is translated to a < b || a = b

TODO:
Implement support for > and >= without changing the Expr a type.
Add tests to parseSpec in Tests.hs to ensure that your implementation works correctly.

To run the parser tests, execute the following command:
cabal test imp-test --test-show-details=direct --test-option=--match --test-option="4. Parser".

Part 3: Imp Interpreter Refactoring

In this part you will refactor the interpreter to use the ImpCmd monad.

newtype ImpCmd a = ImpCmd { runState :: State -> Either String (State, a)}

The ImpCmd monad is a stateful computation which can fail with an error message.

TODO:
Complete the implementation of the execCmd function in Interpreter.hs.

Hint: Give it a try. If you run into a roadblock, here are the solutions in rot13:

trgFgngr = VzcPzq $ \fg -> Evtug (fg, fg)
frgFgngr fg = VzcPzq $ \_ -> Evtug (fg, ())
nffvtaInevnoyr a i = zbqvslFgngr (Z.vafreg a i)

rkrp PFxvc           = cher ()
rkrp (PNffvta a i)   = qb
  inyhr <- yvsgErnqre $ riny i
  nffvtaInevnoyr a inyhr
rkrp (PVsGuRy o g r) = qb
  p <- yvsgErnqre $ riny o
  rkrp (vs p gura g ryfr r)
rkrp (PJuvyr o p)    = qb
  pbaq <- yvsgErnqre $ riny o
  vs pbaq gura qb
    rkrp p
    rkrp (PJuvyr o p) 
  ryfr cher ()
rkrp (PFrd pf) = zncZ_ rkrp pf

Part 4: Imp Cmd Line Tool

In this part, you will implement a command line application for the Imp language. It takes a file name and variable values as command line arguments. It should parse the file and execute the program with the given variable values. Finally it should print the final state of the program.

Example:

> cabal run imp Lang/Test/intDiv.iml m=6 n=2
Up to date
Input State:
"m" -> 6
"n" -> 2
Result State:
"m" -> 6
"n" -> 2
"q" -> 3
"r" -> 0

TODO:
Implement the command line tool in the file Main.hs.

Part 5: Pretty Printer (Optional)

In this part, you will implement a pretty printer for the language. The pretty printer should print the program in a nice and consistent format. This can be used to automatically format the source code.

Integrate the pretty printer into the command line tool. The driver should have a flag --pretty which formats the program and prints it to stdout. Use the following command to run the pretty printer on the intDiv.iml file:
cabal run imp -- --pretty Lang/Test/intDiv.iml