// Matching (), [] and {}
open System;;

let argv = Environment.GetCommandLineArgs();
// argv[2] is first command line arg
let input = argv[2]

let rec matching(stack,index,errs) =
  if index>=input.Length then check_stack stack errs
  else
    match (stack,input[index]) with
      | (_, '(') -> matching(('(',index)::stack, index+1, errs)
      | (_, '[') -> matching(('[',index)::stack, index+1, errs)
      | (_, '{') -> matching(('{',index)::stack, index+1, errs)
      | (('(',_)::s, ')') | (('[',_)::s, ']') | (('{',_)::s, '}') ->
         matching(s,index+1,errs)
      | ((a,i)::b, ')') ->
         printfn "mismatched %c and ) at indices %d and %d" a i index
         matching(b,index+1,errs+1)
      | ((a,i)::b, ']') ->
         printfn "mismatched %c and ] at indices %d and %d" a i index
         matching(b,index+1,errs+1)
      | ((a,i)::b, '}') ->
         printfn "mismatched %c and } at indices %d and %d" a i index
         matching(b,index+1,errs+1)
      | ([], ')') ->
         printfn "unmatched ) at index %d" index
         matching([],index+1,errs+1)
      | ([], ']') ->
         printfn "unmatched ] at index %d" index
         matching([],index+1,errs+1)
      | ([], '}') ->
         printfn "unmatched } at index %d" index
         matching([],index+1,errs+1)
      | (_, x) -> matching(stack,index+1,errs) // skip all other chars

and

  check_stack stack errs = 
    match stack with
      | [] -> 
        if errs=0 then printfn "All brackets match"
        else printfn "There were %d errors" errs
      | ('(',i)::s -> 
        printfn "unmatched ( at index %d" i; check_stack s (errs+1)
      | ('[',i)::s -> 
        printfn "unmatched [ at index %d" i; check_stack s (errs+1)
      | ('{',i)::s -> 
        printfn "unmatched { at index %d" i; check_stack s (errs+1)
      | a::b -> check_stack b errs;;

      
matching([],0,0)