Data commit

Task/Monads-Maybe-monad/Delphi/monads-maybe-monad.delphi

@@ -0,0 +1,74 @@
+program Maybe_monad;
+
+{$APPTYPE CONSOLE}
+
+uses
+  System.SysUtils;
+
+type
+  TmList = record
+    Value: PInteger;
+    function ToString: string;
+    function Bind(f: TFunc<PInteger, TmList>): TmList;
+  end;
+
+function _Unit(aValue: Integer): TmList; overload;
+begin
+  Result.Value := GetMemory(sizeof(Integer));
+  Result.Value^ := aValue;
+end;
+
+function _Unit(aValue: PInteger): TmList; overload;
+begin
+  Result.Value := aValue;
+end;
+
+{ TmList }
+
+function TmList.Bind(f: TFunc<PInteger, TmList>): TmList;
+begin
+  Result := f(self.Value);
+end;
+
+function TmList.ToString: string;
+begin
+  if Value = nil then
+    Result := 'none'
+  else
+    Result := value^.ToString;
+end;
+
+function Decrement(p: PInteger): TmList;
+begin
+  if p = nil then
+    exit(_Unit(nil));
+  Result := _Unit(p^ - 1);
+end;
+
+function Triple(p: PInteger): TmList;
+begin
+  if p = nil then
+    exit(_Unit(nil));
+  Result := _Unit(p^ * 3);
+end;
+
+var
+  m1, m2: TmList;
+  i, a, b, c: Integer;
+  p: Tarray<PInteger>;
+
+begin
+  a := 3;
+  b := 4;
+  c := 5;
+  p := [@a, @b, nil, @c];
+
+  for i := 0 to High(p) do
+  begin
+    m1 := _Unit(p[i]);
+    m2 := m1.Bind(Decrement).Bind(Triple);
+
+    Writeln(m1.ToString: 4, ' -> ', m2.ToString);
+  end;
+  Readln;
+end.