Added programming language fundamentals code. More to come.

OSU Coursework/CS 381 - Programming Language Fundamentals/Homework 4/StackRank.perrenc.hs

@@ -0,0 +1,93 @@
+module StackTypes where
+
+
+--
+-- * Part 1: A Rank-Based Type System for the Stack Language
+--
+-- ** The abstract syntax
+--
+type Prog = [Cmd]
+
+data Cmd = Push Int
+         | Pop Int
+         | Add
+         | Mul
+         | Dup
+         | Inc
+         | Swap
+         deriving(Eq,Show)
+
+type Stack = [Int]
+
+type Rank = Int
+
+type CmdRank = (Int,Int)
+
+
+-- ** The semantic function that yields the semantics of a program
+--
+prog :: Prog -> Stack -> Maybe Stack
+prog []     s = Just s
+prog (c:cs) s = cmd c s >>= prog cs
+
+
+-- ** The semantics function that yields the semantics of a command
+--
+cmd :: Cmd -> Stack -> Maybe Stack
+cmd (Push n) s       = Just (n:s)
+cmd (Pop  k) s       = Just (drop k s)
+cmd Add      (n:k:s) = Just (n + k:s)
+cmd Mul      (n:k:s) = Just (n * k:s)
+cmd Dup      (n:s)   = Just (n:n:s)
+cmd Inc      (n:s)   = Just (n + 1:s)
+cmd Swap     (n:k:s) = Just (k:n:s)
+cmd _        _       = Nothing
+
+
+
+-- | 1. Define the function rankC that maps each stack operation to its rank
+--
+rankC :: Cmd -> CmdRank
+rankC (Push _) = (0, 1)
+rankC (Pop i) = (i, 0)
+rankC (Add) = (2, 1)
+rankC (Mul) = (2, 1)
+rankC (Dup) = (1, 2)
+rankC (Inc) = (1, 1)
+rankC (Swap) = (2, 2)
+
+
+-- | 2. Define the auxiliary function rankP that computes the rank of programs
+--
+rankP :: Prog -> Maybe Rank
+rankP [] = Just 0
+rankP progs = rankProgramHelper progs 0
+
+rankProgramHelper :: Prog -> Rank -> Maybe Rank
+rankProgramHelper [] progs_rank = Just progs_rank
+rankProgramHelper (progs_head:progs_tail) progs_rank = 
+    let (current_pops, curent_pushes) = rankC progs_head in
+    if current_pops <= progs_rank then rankProgramHelper progs_tail (progs_rank + curent_pushes - current_pops)
+    else Nothing
+
+-- | 3. Define the semantic function semStatTC for evaluating stack programs
+--
+semStatTC :: Prog -> Maybe Stack
+semStatTC prog_list = 
+    if (rankP prog_list) /= Nothing then prog prog_list []
+    else Nothing
+
+
+-- | EXTRA CREDIT
+--
+prog' = undefined
+
+
+
+-- * Part 2: Runtime Stack
+--
+
+
+
+-- * Part 3: Static and Dynamic Scope
+--