diff --git a/src/main.lisp b/src/main.lisp
index 2940bb3..b8b9065 100644
--- a/src/main.lisp
+++ b/src/main.lisp
@@ -66,6 +66,7 @@
 ; db/new ensures directory '<path>/data/' exist,
 ; then loads values from existing files, if any, and puts them into db-data.
 (defun db/new (path)
+  (declare (type string path))
   (let ((data          (make-hash-table))
         (data-dir-path (concatenate 'string path "/data/"))
         (current-index 0))
@@ -92,12 +93,15 @@
   (concatenate 'string dbpath "/indexes/by_" index-name "/"))
 
 ; Example: returns "./storage/cars/partitions/by_color/Red/".
+(declaim (ftype (function (string string string) string) db/partition/get-directory-path))
 (defun db/partition/get-directory-path (dbpath name object-attribute)
-  (let ((value (value->safe-string object-attribute)))
-    (concatenate 'string dbpath "/partitions/by_" name "/" value "/")))
+  (declare (type string dbpath name object-attribute))
+  (concatenate 'string dbpath "/partitions/by_" name "/" object-attribute "/"))
 
 ; Example: "./storage/cars/" "name" #'vehicle-name object -> "./storage/cars/indexes/by_name/Corvet".
 (defun db/index/get-symlink-path (dbpath index-name fsymbol object)
+  (declare (type string dbpath index-name))
+  (declare (type symbol fsymbol))
   (let* ((value            (funcall fsymbol object))
          (symlink-basename (value->safe-string value)))
     (concatenate 'string
@@ -109,7 +113,10 @@
 ;          :target "../../data/0000000015"
 ;          :hard nil)
 (defun db/index/new (dbpath index-name fsymbol object file-name)
+  (declare (type string dbpath index-name file-name))
+  (declare (type symbol fsymbol))
   (let ((symlink-path (db/index/get-symlink-path dbpath index-name fsymbol object)))
+    (declare (type string symlink-path))
 
     ; works even when the database directory is moved
     (osicat:make-link symlink-path
@@ -117,22 +124,28 @@
       :hard nil)))
 
 (defun db/index/del (dbpath index-name fsymbol object)
+  (declare (type string dbpath index-name))
+  (declare (type symbol fsymbol))
   (delete-file (db/index/get-symlink-path dbpath index-name fsymbol object)))
 
 ; Example: "./storage/cars/" "color" #'vehicle-color object "0000000015".
 ;   -> "./storage/cars/partitions/by_color/Red/0000000015".
 (defun db/partition/get-symlink-path (dbpath partition-name fsymbol object file-name)
-  (concatenate 'string
-    ; example: "./storage/cars/partitions/by_color/Red/"
-    (db/partition/get-directory-path dbpath partition-name (funcall fsymbol object))
-    ; example: "0000000015"
-    file-name))
+  (declare (type string dbpath partition-name file-name))
+  (declare (type symbol fsymbol))
+  (let* ((object-attribute (funcall fsymbol object))
+         (safe-value (value->safe-string object-attribute))
+         ; example: "./storage/cars/partitions/by_color/Red/"
+         (dirpath    (db/partition/get-directory-path dbpath partition-name safe-value)))
+  (concatenate 'string dirpath file-name)))
 
 ; Example: "./storage/cars/" "color" #'vehicle-color object "0000000015"
 ;   -> (osicat:make-link "./storage/cars/partitions/by_color/Red/0000000015"
 ;          :target "../../../data/0000000015"
 ;          :hard nil)
 (defun db/partition/new (dbpath partition-name fsymbol object file-name)
+  (declare (type string dbpath partition-name file-name))
+  (declare (type symbol fsymbol))
   (let ((symlink-path
       (db/partition/get-symlink-path dbpath partition-name fsymbol object file-name)))
 
@@ -144,9 +157,13 @@
       :hard nil)))
 
 (defun db/partition/del (dbpath partition-name fsymbol object file-basename)
+  (declare (type string dbpath partition-name file-basename))
+  (declare (type symbol fsymbol))
   (delete-file (db/partition/get-symlink-path dbpath partition-name fsymbol object file-basename)))
 
 (defun db/new-index (database index-name fsymbol)
+  (declare (type string index-name))
+  (declare (type symbol fsymbol))
   (let ((dbpath (db-path database))
         (index-name (value->safe-string index-name)))
     ; create a directory for the indexes
@@ -164,6 +181,8 @@
       (db-data database))))
 
 (defun db/partition/update (dbpath partition-name fsymbol object file-name old-object)
+  (declare (type string dbpath partition-name file-name))
+  (declare (type symbol fsymbol))
   (let ((new-value (funcall fsymbol object))
         (old-value (funcall fsymbol old-object)))
     (if (not (equal new-value old-value))
@@ -174,6 +193,8 @@
         (db/partition/new dbpath partition-name fsymbol     object file-name)))))
 
 (defun db/new-partition (database partition-name fsymbol)
+  (declare (type string partition-name))
+  (declare (type symbol fsymbol))
   (let ((dbpath         (db-path database))
         (partition-name (value->safe-string partition-name)))
     ; create a directory for the partitions
@@ -191,7 +212,9 @@
       (db-data database))))
 
 ; Example: "./storage/cars/data/000000000000018".
+(declaim (ftype (function (string string) string) get-filepath))
 (defun get-filepath (dbpath file-name)
+  (declare (type string dbpath file-name))
   (concatenate 'string dbpath "/data/" file-name))
 
 (defun db/add (database object)
@@ -223,6 +246,7 @@
   (db-current-index database))
 
 (defun db/del (database object-index)
+  (declare (type integer object-index))
   (let ((file-basename (number->filename object-index))
         (dbpath        (db-path database))
         (object        (gethash object-index (db-data database))))
@@ -244,6 +268,7 @@
 
 ; Search for the data from the FS.
 (defun db/get-by-index (database index-name attribute-value)
+  (declare (type string index-name))
   (let ((value (value->safe-string attribute-value)))
     (filename->integer
       (osicat:read-link
@@ -252,12 +277,15 @@
 
 ; Search for the data from the FS.
 (defun db/get-by-partition (database name attribute-value)
+  (declare (type string name))
   (let ((value (value->safe-string attribute-value))
         (dbpath (db-path database)))
     (loop for filename in (osicat:list-directory (db/partition/get-directory-path dbpath name value))
           collect (filename->integer filename))))
 
 (defun db/index/update (dbpath index-name fsymbol object file-name old-object)
+  (declare (type string dbpath index-name file-name))
+  (declare (type symbol fsymbol))
   (let ((new-value    (funcall fsymbol object))
         (old-value    (funcall fsymbol old-object))
         (symlink-path (db/index/get-symlink-path dbpath index-name fsymbol object)))
@@ -274,6 +302,7 @@
 ; TODO: check database integrity (redundancy)
 ; TODO: locking
 (defun db/update (database object-index)
+  (declare (type integer object-index))
   (let* ((object            (gethash object-index (db-data database)))
          (dbpath            (db-path database))
          (file-basename     (number->filename object-index))