Pascaligo map iteration issue

Question

I try to fetch a list of addresses with expired date by appending the address to list(address). However when doing map iteration, it encounters a persistent error says 'not True'.

Hope someone can guide a bit here. Thanks in advance!

Below is part of the code:

function checkPoint (var s : contract_storage) : contract_storage is 
 begin
   function iter_op (const m : register) : list(address) is
    block {
      const removing_list : list(address) = list [];
      function iterated (const i : address; const j : counter) : list(address) is
        if j.maturityTime <= Tezos.now then i # removing_list else removing_list;
    } with Map.iter (iterated, m);  //error says: characters 11-33. Not true
   const remove_creditors : list(address) = iter_op (s.creditorsMap);  //creditorsMap is  map (address, counter)
   //...
   // if above is bug free, I will start to remove the list of items in the map one by one 
 end with s

Answer 1

the fold operation would be a fit...

const removing_list : list(address) = list [];

function fold_op (const m : register) : list(address) is
  block {
    function folded (const i : list(address); const j : address * counter) : list(address) is
      if j.1.maturityTime <= Tezos.now then j.0 # i else i;
  } with Map.fold (folded, m, removing_list)


function checkPoint (var s : contract_storage) : contract_storage is 
 begin
   const remove_creditors : list(address) = fold_op (s.creditorsMap); // the crucial part
   s := List.fold (removeCreditor, remove_creditors, s); //other operations irrelevant to the question
 end with s