Tag Archives: Yaclot

Yaclot 0.1.2: Extended Date Conversions

I released a new version of my Clojure conversion and map transformation library to Clojars. It includes two new features:

1. Added natural conversion between Long and Date.

2. You can pass a collection of formats for converting String to Date. It attempts parsing with each of the formats and returns first result which didn’t throw ParseException.

  (using-format ["yyyy-MM-dd" "M/dd/yy"]
    (to-type java.util.Date)))
; => #<Date Sat Feb 12 00:00:00 CET 2011>


Yaclot 0.1.0 Released (Clojure Conversion and Record Transformation Library)

I released Yaclot 0.1.0 to Clojars. This version can be used to convert single values as well as records.

Converting individual values looks like:

(convert "2011-02-12" (to-type java.util.Date))
; => #<Date Sat Feb 12 00:00:00 CET 2011>

(convert "2/12/11"
    (using-format "M/dd/yy" (to-type java.util.Date)))
; => #<Date Sat Feb 12 00:00:00 CET 2011>

(convert 5000.42 (to-type String (using-format "%,.2f")))
; => "5,000.42"

Order of using-format and to-type doesn’t matter. using-format is optional (default for dates is yyyy-MM-dd).

You can also use it to convert records in a single operation:

  {:dt "2011-02-12" :int 42 :label "Label"}    ; Record
  {:dt  (to-type java.util.Date)               ; Desired types
   :int (to-type String)})
; => {:dt #<Date Sat Feb 12 00:00:00 CET 2011>, :int "42", :label "Label"}

The project originated from a pet web application, where I needed to deal with parsing and formatting numbers and dates between the “presentation”, “business logic” and “database” layers.

To learn more about motivation, features and syntax, take a look at the draft in my previous post.

This version supports conversions between String, Date and numeric types. Next on the road map is exception-free error handling with local bindings and validation.

See also:

Designing Yaclot: Generic Clojure Conversion Library

In real Clojure applications you often cannot avoid explicit type conversions, even though the language does not require you to explicitly specify types all the time. Another great feature of Clojure is its universal data structure: most of the time you don’t need anything more than a simple map or record. However, these records often need to be a bit different in different areas of the applications.


Examples? You may have a java.sql.Date in database and backend, but your web front end provides you with a String. Or your backend uses rational numbers, but you need to format them into nice Strings for presentation.

Sometimes you operate on whole records. From database you may pull the following:

(def db-sample
  {:date    2011-02-01 ; java.sql.Date
   :balance 2042.00    ; java.math.BigDecimal
   :credit  1000.00    ; java.math.BigDecimal
   :roi     2.13 })    ; java.math.BigDecimal

… for display you would like to use:

(def presentation-sample
  {:date    "Feb 1, 2011" ; String
   :balance "$2,042.00"   ; String
   :credit  "$1,000.00"   ; String
   :roi     "2.13%" })    ; String

… and you need to support input from a web form as:

(def form-sample
  {:date    "2011-02-01"  ; String
   :balance "2042"        ; String
   :credit  "1000"        ; String
   :roi     nil })        ; Rational calculated 
                          ; by back-end from other fields

All three have very similar structure, but implementing all these transformations can be pain.

Planned API for generic converter

I am implementing a library that will do it for you, with API similar to the following:

(def db-fmt
  {:date    (to-type java.sql.Date)
   :balance (to-type java.math.BigDecimal)
   :credit  (to-type java.math.BigDecimal)
   :roi     (to-type java.math.BigDecimal) })

(def presentation-fmt
  {:date    (using-format "MMM d, yyyy" (to-type String))
   :balance (using-format "$%.2f"       (to-type String))
   :credit  (using-format "$%.2f"       (to-type String))
   :roi     (using-format "%.2f%%"      (to-type String)) })

(def form-fmt
  {:date    (using-format "yyyy-M-d" (to-type java.sql.Date))
   :balance                          (to-type java.math.BigDecimal)
   :credit                           (to-type java.math.BigDecimal) })

(map-convert db-sample presentation-fmt)
=> ; (similar to presentation-sample)

(map-convert form-sample db-fmt)
=> ; (similar to db-sample)

Another feature is generic conversion function for individual values:

(convert "2011-02-12" (to-type java.util.Date))
; => #&lt;Date Sat Feb 12 00:00:00 CET 2011&gt;

(convert (java.util.Date. 111 1 12) (to-type String))
; => "2011-02-12"

(convert 42 (to-type String))
; => "42"

(convert "2/12/11" (using-format "M/dd/yy" (to-type java.util.Date)))
; => #&lt;Date Sat Feb 12 00:00:00 CET 2011&gt;

Ideas for the Future

In the future, this library could support pre- and post-conversion validation. For instance, check that balance is not empty and date is in the correct format before conversion, and validate that balance and credit are positive once they are numbers.

Another idea is using it as a base for yet another HTML form manipulation library. I found existing libraries somewhat disappointing as they imposed to many restrictions on me. I would like to have the ability to manipulate and lay out forms as I please, and only use the bits of the library that I need right now.

Current Status

Currently much of the API and features are designed, but only the above presented part is implemented (not even supporting formats for numbers, only for dates). Once I implement conversions between all popular/basic types I will mark it 0.1 and push to Clojars. Error handling and validation are next on the road map.

The code is available at github.

Feel free to share any comments or ideas.