Added programming language fundamentals code. More to come.

OSU Coursework/CS 381 - Programming Language Fundamentals/Homework 2/MiniLogo.perrenc.hs

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+module MiniLogo where
+
+import Data.List
+
+--
+-- * MiniLogo
+--
+-- | The grammar:
+--      num ::= (any natural number)
+--      var ::= (any variable name)
+--    macro ::= (any macro name)
+--
+--     prog ::= ε | cmd; prog                 sequence of commands
+--
+--     mode ::= up | down                     pen status
+--
+--     expr ::= var                           variable reference
+--           |  num                           literal number
+--           |  expr + expr                   addition expression
+--
+--      cmd ::= pen mode                      change pen status
+--           |  move (expr, expr)             move pen to a new position
+--           |  define macro (var*) {prog}    define a macro
+--           |  call macro (expr*)            invoke a macro
+
+-- | 1. Define the abstract syntax as a set of Haskell data types.
+type Var = String
+type Macro = String
+
+type Prog = [Cmd]
+
+data Mode = Up
+          | Down
+          deriving (Show, Eq)
+
+data Expr = VarRef Var
+          | LitNum Int
+          | Add Expr Expr
+          deriving (Show, Eq)
+
+data Cmd = Pen Mode
+         | Move (Expr, Expr)
+         | Define Macro [Var] Prog
+         | Call Macro [Expr]
+         deriving (Show, Eq)
+
+
+-- | 2. Define a MiniLogo macro "line."
+--
+--      Concrete syntax in a comment:
+--
+--      define line(x1, y1, x2, y2) {
+--          pen up;
+--          move (x1, y1);
+--          pen down;
+--          move (x2, y2);
+--          pen up;
+--      }
+--
+--      Abstract syntax in code (include correct type header):
+--
+line :: Cmd
+line = Define "line" ["x1", "y1", "x2", "y2"] [Pen Up, Move (VarRef "x1", VarRef "y1"), Pen Down, Move (VarRef "x2", VarRef "y2"), Pen Up]
+
+-- | 3. Define a MiniLogo macro "nix" using "line" defined above.
+--
+--      Concrete syntax in a comment:
+--
+--      define nix(x, y, w, h) {
+--          line(x, y, x + w, y + h);
+--          line(x + w, y, x, y + h);
+--      }
+--
+--      Abstract syntax in code (include correct type header):
+--
+nix :: Cmd
+nix = Define "nix" ["x", "y", "w", "h"]
+                   [Call "line" [VarRef "x", VarRef "y", Add (VarRef "x") (VarRef "w"), Add (VarRef "y") (VarRef "h")],
+                    Call "line" [Add (VarRef "x") (VarRef "w"), VarRef "y", VarRef "x", Add (VarRef "y") (VarRef "h")]]
+
+
+-- | 4. Define a Haskell function "steps" (steps :: Int -> Prog) that draws
+--      a staircase of n steps starting from (0,0).
+--
+steps :: Int -> Prog
+steps 0 = []
+steps i = [Call "line" [LitNum i, LitNum i, LitNum (i - 1), LitNum i], Call "line" [LitNum i, LitNum i, LitNum i, LitNum (i - 1)]] ++ steps (i-1)
+
+
+-- | 5. Define a Haskell function "macros" (macros :: Prog -> [Macro] that
+--      returns a list of the names of all the macros that are defined anywhere
+--      in a given MiniLogo program.
+--
+macros :: Prog -> [Macro]
+macros [] = []
+macros (h:t) = case h of
+             Define m _ _ -> m : macros t
+             otherwise -> macros t  
+
+
+-- | 6. Define a Haskell function "pretty" (pretty :: Prog -> String) that
+--      "pretty-prints" a MiniLogo program.
+--
+pretty :: Prog -> String
+pretty [] = ""
+pretty (Pen Up:t) = "pen up;\n" ++ pretty t
+pretty (Pen Down:t) = "pen down;\n" ++ pretty t
+pretty (Move (x, y):t) = "move (" ++ exprString x ++ ", " ++ exprString y ++ ");\n" ++ pretty t
+pretty (Call n h:t) = n ++ "(" ++ intercalate ", " (map exprString h) ++ ");\n" ++ pretty t
+pretty (Define m h p:ps) = "define " ++ m ++ "(" ++ intercalate ", " h ++ ") {\n" ++ pretty p ++ "}\n" ++ pretty ps
+
+exprString :: Expr -> String
+exprString (Add x y) = exprString x ++ " + " ++ exprString y
+exprString (LitNum n) = show n
+exprString (VarRef s) = s
+
+--
+-- * Bonus Problems
+--
+-- | 7. Define a Haskell function "optE" (optE :: Expr -> Expr) that partially
+--      evaluates expressions by replacing additions of literals with the
+--      result.
+--
+optE = undefined
+
+
+-- | 8. Define a Haskell function "optP" (optP :: Prog -> Prog) that optimizes
+--      all of the expressions contained in a given program using optE.
+--
+optP = undefined