From eb84dace85b56ba8366f31e64da0ef01af20ab24 Mon Sep 17 00:00:00 2001
From: Alexander Kuzmin <treflcrew@gmail.com>
Date: Sat, 6 Jun 2026 17:16:37 +0400
Subject: [PATCH] Parse timestamp strings in heuristicate-types

---
 src/properties.lisp | 10 +++++++---
 src/utils.lisp      | 13 +++++++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/src/properties.lisp b/src/properties.lisp
index 13a9779..efd34a8 100644
--- a/src/properties.lisp
+++ b/src/properties.lisp
@@ -10,9 +10,13 @@ Often when reading in a data set, the types will be inconsistent in a variable.
   (let ((name (name df)))
     (map nil #'(lambda (key)
 		 (let* ((data     (column df key))
-			(col-type (column-type data))
-			(sym (find-symbol (symbol-name key) (find-package name))))
-		   (setf (get sym :type) col-type)))
+				(col-type (column-type data))
+				(sym (find-symbol (symbol-name key) (find-package name))))
+		   (setf (get sym :type) col-type)
+		   ;; If a column is :temporal, replace strings in it with timestamps.
+		   ;; If local-time fails to parse a value then signal an error without corrupting the dataframe.
+		   (when (eql col-type :temporal)
+			 (setf (column df key) (map 'vector #'local-time:parse-timestring data)))))
 	 (keys df))))
 
 (defun set-properties (df property prop-values)
diff --git a/src/utils.lisp b/src/utils.lisp
index 92ac365..aba53de 100644
--- a/src/utils.lisp
+++ b/src/utils.lisp
@@ -9,6 +9,17 @@
 ;;; cl:type-of is under-constrained and returns implementation
 ;;; specific results, so we use our own version
 ;;; See: https://www.cs.cmu.edu/Groups/AI/html/cltl/clm/node53.html
+
+
+(defun timestamp-string-p (string)
+  "Return T if STRING can be parsed as a timestamp by LOCAL-TIME."
+  (and (stringp string)
+       (when (local-time:parse-timestring string :fail-on-error nil)
+		 t)))
+
+(deftype timestamp-string ()
+  '(satisfies timestamp-string-p))
+
 (defun get-type (x)
   "Return the most specific type symbol for x"
   (typecase x
@@ -22,6 +33,7 @@
     ;; (rational 'cl:rational)		;SBCL doesn't recognise this return type
     ;; (real    'real)			;SBCL doesn't recognise this return type
 
+	(timestamp-string 'temporal)
     (simple-string 'simple-string)
     (string 'string)
 
@@ -54,6 +66,7 @@
 	  ((member 'fixnum  type-list) :fixnum)
 	  ((member 'integer type-list) :integer)
 	  ((member 'string  type-list) :string)
+	  ((member 'temporal  type-list) :temporal)
 	  ((member 'bit     type-list) :bit)
 	  ((member 'symbol  type-list) :symbol)
 	  (t 'string ))))