Pascaligo Compiling Error on Big_map.add

Question

I encounter the below error message when compiling the code on LIGO Playground.

Error: ligo: in file "tmp-1CAIKM1VUeRgb.ligo", 
line 29, characters 98-112. different kinds:  {"a":"unit","b":"(type_operator: Big Map (address,record[creditAmount -> nat , initialTime -> timestamp]))"}

which is for line starting as Big_map.add...

function addCreditor (const creditor : address ; const lendingValue : nat ; var s : contract_storage) : contract_storage is
 begin
  // If debtor and the creditor is same, skip
  if s.debtor = creditor then skip;
  else block {
      case (Map.find_opt (creditor, s.creditorsMap)) of
        // if creditor is found, he cannot participate in again.
        | Some (c) -> 
          failwith("Creditor contract does not reach maturity")
        // if no record found, add it
        | None -> {
          s.totalCredits := s.totalCredits + lendingValue;
          Big_map.add(creditor, record [ initialTime = Tezos.now ; creditAmount = lendingValue ], s.creditorsMap)
        }
      end;
  }
 end with s

The relevant declaration,

type counter is record
    initialTime : timestamp;
    creditAmount : nat;
end

type action is
| AddCreditor of (address * nat)
| RemoveCreditor of (address)

type contract_storage is record
  debtor : address;
  totalCredits : nat;
  creditorsMap : big_map(address, counter);
end

The main function,

 function main (const p : action ; const s : contract_storage) :
  (list(operation) * contract_storage) is
 block { 
   // Reject any transaction that try to transfer token to this contract
   if amount =/= 0tz then failwith ("This contract do not accept token");
   else skip;
  } with case p of
  | AddCreditor(n) -> ((nil : list(operation)), addCreditor(n.0, n.1, s))
  | RemoveCreditor(n) -> ((nil : list(operation)), removeCreditor(n.0, s))
 end

Answer 1

The one I raised the question above, map.add is not a function that returns a map, instead it returns unsigned int. So, one of the correct ways is,

function addCreditor (const creditor : address ; const lendingValue : nat ; var s : contract_storage) : contract_storage is
 begin
  // If debtor and the creditor is same, skip
  if s.debtor = creditor then failwith("Creditor contract does not exist");
  else block {
      case s.creditorsMap[creditor] of
        // if creditor is found, he cannot participate in again.
        | Some (c) -> 
          failwith("Creditor contract does not reach maturity")
        // if no record found, add it
        | None -> {
          const logging : counter =
              record [
                initialTime       = Tezos.now;
                creditAmount = lendingValue;
              ];
          const updated_map : register = Map.add(creditor,logging,s.creditorsMap);
          s.creditorsMap := updated_map;
          s.totalCredits := s.totalCredits + lendingValue;
        }
      end;
  }
 end with s

Also, set aside the above issue, a few more bugs were consecutively found