The first regex is returning an empty list not nil.
David
On Mon, Mar 9, 2009 at 11:48 AM, timc <[email protected]> wrote:
>
> 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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