Can someone please see what's wrong with this.
(defn getArg [arg]
"Return a [keyword value] depending on the form of the string arg:
1. arg is of the form +x ==> [:x true].
2. arg is of the form -x ==> [:x false].
3. arg is of the form x=v ==> [:x v].
4. else ==> [:files arg]."
(let [x (or
(re-seq #"([+])([a-zA-Z_0-9]+)" arg)
(re-seq #"([-])([a-zA-Z_0-9]+)" arg)
(re-seq #"([a-zA-Z_0-9]+)=([^ ]+)" arg))]
(if (nil? x) [:files arg]
(let [x (first x)
y (nth x 1)
z (nth x 2)]
(cond
(= y "+") [(keyword z) true]
(= y "-") [(keyword z) false]
:else [(keyword y) z])))))
This is part of a command-line-arg processing function. I want to end
up with a map containing things like this:
{:verbose true :fast false :configFile "/tom/dick" :files ["foo" "bar"
"zot"]}
as a result of processing the command line args:
+verbose -fast configFile=/tom/dick foo bar zot
Now...
(getArg "+foo") correctly returns [:foo true]
however
(getArg "-foo") throws a NullPointerException.
Am I wrong in my understanding of the or function? That is, that (or a
b c) should return the first of a,b,c that returns true (i.e. non-nil)
or nil if they are all nil?
Or is something happening to the function 'arg' inside the let?
Thanks in advance.
---------------------------------------
In case it's interesting to anyone, the other part of this (that calls
getArg) is the following.
(defn getArgs [args & xs]
"This processes args (a seq of strings) and returns a map.
The parameter xs is a seq of two-element vectors: [keyword value].
The returned map contains (keyword,value) pairs produced by
processing the args, as follows.
1. An arg of the form +x creates the pair (:x true).
2. An arg of the form -x creates the pair (:x false).
3. An arg of the form x=v creates the pair (:x v), where v is a
string.
4. Any other args will be placed in the pair (:files
vectorOfStrings).
5. Any [x v] in xs, not found in the args, will create the pair (:x
v)."
(let [res {:files []}]
; First process the args (if any).
(when args (doall (for [arg args]
(let [ga (getArg arg) [key val] ga]
(cond
(= key :files) (conj (:files res) val)
:else (conj res ga))))))
; Now process the xs (if any).
(when xs (doall (for [x xs]
(let [key (first x)]
(when (not (key res)) (conj res x))))))
res))
so that (for example)
(def cmdArgs (getArgs *command-line-args* [[:verbose false] [:fast
true] [:configFile "/tom/harry"] [:something "someValue"]]))
both gets command line params into the map cmdArgs and/or creates
entries with default values. What is does NOT do is validate the
parameters.
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