Determining Why Clojure REPL (load-file) and cake build yield error

Question

Since Clojure 1.3, I am confused about the directory structure needed to build something in Clojure. I am using cake to build and cake repl.

Here is what works. I have a working build directory addr_verify. The main's and ns's name is addr-verify. The project.clj refers to addr-verify as main, and in addr_verify/src there is addr_verify.clj. The ns inside addr_verify.clj refers to the addr-verify name space.

Now, I had a directory mr1, but cake won't compile it right at line 1

(ns mr1
  (use ['clojure.string :only '(split)])
  (use ['clojure.string :only '(join)])
  )

If mr1 is a bad name, what naming convention should I use?

I have tried mr1_app as a directory structure using mr1-app as the main name and ns name. I

For mr1 as the directory and ns name, I get

Caused by: clojure.lang.Compiler$CompilerException: java.lang.ClassCastException: clojure.lang.PersistentList cannot be cast to java.lang.Comparable, compiling:(mr1.clj:1)

I'm just not getting what I'm doing wrong here, and I know it's probably something really simple.

Edit:

Why does the binary mr1 not have a main?

mr1/project.clj

(defproject mr1 "0.0.1-SNAPSHOT"
  :description "TODO: add summary of your project"
  :dependencies [[org.clojure/clojure "1.3.0"]
                 [org.clojure/tools.cli "0.1.0"]]
   :main mr1)

mr1/src/mr1.clj

(ns mr1
    (:use [clojure.string :only [split]]
          [clojure.string :only [join]]))

(def grid-dim (atom '(0 0)))
(def mr1-pos (atom '(0 0)))
(def mr2-pos (atom '(0 0)))

(defn cvt-str-to-int
    [string]
   (map #(Integer/parseInt %)
    (split string #" ")))

(defn prompt-for-grid-dim
    []
    (do
        (println "Enter the dimensions of the grid (10 10) ")
        (cvt-str-to-int (read-line))
    ))

(defn prompt-for-rover-pos
    [rover-num]
    (do
        (println "Enter rover's initial position on the grid (2 4) ")
        (cvt-str-to-int (read-line))
    ))

(defn prompt-for-rover-moves
    []
    (do
        (println "Enter rover's moves LMMRM ")
        (read-line)
    ))

(defn -main 
    [& args]
    (do
       (reset! grid-dim (cvt-str-to-int (prompt-for-grid-dim)))
       (reset! mr1-pos (cvt-str-to-int (prompt-for-rover-pos)))
    ) 
)

Answer 1

I think there is something wrong with the "syntax" of your namespace declaration. Instead, try this:

(ns mr1
    (:use [clojure.string :only [split]]
          [clojure.string :only [join]]))

Change your :main setting in project.clj accordingly: it should just be mr1, contrary to what I said earlier.

Edited according the comment of googolplex

Answer 2

Since the first part has already been answered, I will answer the part about :main. As sample.project.clj file says, :main key should have as an assigned value a namespace which contains -main function. So you should have such function

(defn -main [& args]
  (do-things-you-want-to-do-on-program-start))

in your mr1.clj. Also AFAIR if you want to use your program as a standalone jar you have to have this namespace gen-classed. By this I mean that you have to:

1. Include :gen-class option in your namespace definition like this:

   (ns mr1
     (:gen-class)
     ...other options...)
   

2. Make the namespace AOT-compiled (AOT stands for Ahead Of Time). To do this you need to specify your namespace in the list of AOT-compiled namespaces in project.clj:

   (defproject mr1 "0.0.1-SNAPSHOT"
     ...other definitions...
     :aot [mr1]
     :main mr1)
   

After you've done this, you can use cake to generate executable jar for you.

ADD: I think it is worth to note that you don't have to have a :main at all. If all you want to do is to run your program in repl or if you want to create a library, there can be no gen-classes namespaces (except if you want to interact with plain java code in such a way that java code can call your clojure code) and no :main namespace, which are required only for executable jars.