How to show error on missing parameters for options? - clojure

Question

I'm an absolute Clojure beginner and I'm trying to build a CLI app using the clojure.tools.cli library.
My problem is that I can't show any error when an option is not provided with required parameter.
What I want:
$ java -jar test.jar -m SAMPLE
Given file: SAMPLE
$ java -jar test.jar -m
ERROR: Please provide a file
What happens:
$ java -jar test.jar -m SAMPLE
Given file: SAMPLE
$ java -jar test.jar -m
$
It doesn't show anything.
Here is my code:
(ns obmed-clj.core
(:require [clojure.tools.cli :refer [parse-opts]])
(:gen-class))
(def cli-options
[["-m" "--menu FILE" "Provide menu file path"
:parse-fn #(if (nil? %)
(println "ERROR: Please provide a file")
%)
:validate-fn #(println "Given file:" %)]])
(defn -main [& args]
(parse-opts args cli-options))

Answer 1

You are abusing the -fn arguments here a little. Their use is to convert the "string" (in your case, since you have "--menu FILE") and then do additional validation on that (but rather use :validate [fn msg] instead). So e.g.:
user=> (def cli-opts [["-m" "--menu FILE" "menu file"
:parse-fn #(java.io.File. %)
:validate [#(.exists %) "file must exist"]]])
#'user/cli-opts
Missing argument:
user=> (parse-opts ["-m"] cli-opts)
{:arguments [],
:errors ["Missing required argument for \"-m FILE\""],
:options {},
:summary " -m, --menu FILE menu file"}
File not existing:
user=> (parse-opts ["-m" "XXX"] cli-opts)
{:arguments [],
:errors ["Failed to validate \"-m XXX\": file must exist"],
:options {},
:summary " -m, --menu FILE menu file"}
All is well:
user=> (parse-opts ["-m" "/etc/hosts"] cli-opts)
{:arguments [],
:errors nil,
:options {:menu #<java.io.File#34d63c80 /etc/hosts>},
:summary " -m, --menu FILE menu file"}