[Haskell-beginners] Converting an imperative program to haskell

[Hein Hundal]

Hi,

   I am new to Haskell.  I programmed in imperative languages 
for many years and I have been using Mathematica for the last 
15 years which mixes functional and imperative programming.  
I started learning Haskell about 2 months ago mostly by reading 
the first 13.5 chapters of Real World Haskell and doing about 50 
of the Euler Problems.  "The Evolution of a Haskell Programmer", 
the Haskell Wiki, and this listserv have also been helpful.

   I figured I should try a larger program in Haskell, so I am
converting one of my Mathematica programs, a simulator for the 
card game Dominion, over to Haskell.  Most of that is going well except for one patch of imperative code.  My Haskell version of 
this code is ugly.  I was hoping someone could recommend a better 
way to do it.  I will paste a simplified version of the code 
below.  If necessary, I can provide all the other code used for 
this simplified example (about 30 more lines of Haskell code, or 
an equivalent program in C++ (130 lines of code).

Cheers,
Hein

-----------------Ugly Haskell Code-------------------------
data LoopState = LSt GameState Strat Int Int Int [Int] Int Int Bool

proc :: GameState -> Strat -> (Int, Int, GameState)
proc gs' strat = let 
      iA     = 1
      iTh    = 0
      i      = 0 
      aA     = replicate 20 0
      iB     = 1
      iC     = 0
      bDone  = False 
      gs     = apps ("<<<"++show(gs')++">>>") gs'
      lst    = LSt gs strat iA iTh i aA iB iC bDone
      lst2   = until isDone procloop lst  
      isDone  (LSt gs strat iA iTh i aA iB iC bDone) = bDone
      output  (LSt gs strat iA iTh i aA iB iC bDone) = (iB, iC, appd aA gs)
  in output lst2


procloop :: LoopState -> LoopState
procloop (LSt gs' strat iA iTh i aA iB iC bDone) = do
   let iCd = stratchoose strat gs' iA iTh iB aA
   let gs = apps ("iB "++show iB++ "\n" ) gs'
   if iA<=0 || i>=20 || actcd gs <=0 || iCd == -1 
      then LSt gs strat iA iTh (i+1) aA iB iC True
      else if iCd == 1 
         then LSt gs strat iA (iTh+1) (i+1) aA iB iC False
         else let
              gs2 = delh iCd gs
              aA2 = append aA iCd
              (iA3, iC3, iB3, gs3, aA3) = doAct iA  iC  iB  gs2 aA2 strat iCd
              (iA4, iC4, iB4, gs4, aA4) = doAct iA3 iC3 iB3 gs3 aA3 strat iCd
           in if iTh>0 
              then LSt gs4 strat iA4 (iTh-1) (i+1) aA4 iB4 iC4 False
              else LSt gs3 strat iA3 (iTh-1) (i+1) aA3 iB3 iC3 False


---------------end of Haskell code-------------------------------