ah, compare > (if-let [{errors :email} (function-returning-error email password)] > true > false)
with (let [{errors :email) (function-returning-errros email password)] (if errors true false)) I'm not saying that if-let is wrong, I'm saying I would never use in such a case (i.e. restructuring), because it led me think wrong. mimmo On Jan 30, 2013, at 10:23 AM, Mimmo Cosenza <mimmo.cose...@gmail.com> wrote: > Uhm, I do not agree. > > Suppose tha you have a function returning a map of errors (a valip validator > lib real case) like the following > > {:email ["Email can't be empty"] :password ["Password can't be empty"]} > > If I want to select just the email errors I would write something like that > > (if-let [{errors :email} (function-returning-error email password)] > true > false) > > Reading the above code you're led to believe that if there are email errors, > errors local binding will be true. Instead, it returns true even if the are > no email errors but there are password errors and you never get the false > branch. > > An if you want to catch password errors you would write something like > > (if-let [{errors :password} (function-returning-errors email password)] > true > false) > > In either case you never get the false branch when function-returning-errors > return an error which is not the one you're looking for > > Mimmo > > > On Jan 30, 2013, at 10:05 AM, James Xu <xumingming64398...@gmail.com> wrote: > >> From the expansion we can see that if-let determine the result based on >> the second param, in your case: {:key2 "a string"}, not the local binding >> you assumed(key1), and >> I think it is reasonable, for example, if we have the following code: >> >> (if-let [{key1 key2} {:key2 "a string"}] >> true >> false)) >> >> >> Should if-let determine the result based on key1? key2? IMO {key1 key2} in >> a whole is more reaonable. And {key1 key2} == {:key2 "a string"}, then the >> result is true. >> >> >> >> On 13-1-30 下午4:51, "Mimmo Cosenza" <mimmo.cose...@gmail.com> wrote: >> >>> Hi all, >>> I'm a little bit confused about the semantic of if-let macro. >>> >>> Suppose to call it as follows with map destructoring: >>> >>> (if-let [{key1 :key1} {:key2 "a string"}] >>> true >>> false)) >>> >>> It returns true. >>> >>> But, >>> >>> (let [{key1 :key1} {:key2 "a string"}] >>> (if key1 >>> true >>> false)) >>> >>> returns false. >>> >>> >>> The macro expansion of the former explains why >>> >>> (macroexpand-1 '(if-let [{key1 :key1} {:key2 "a string"}] true false)) >>> >>> returns >>> (clojure.core/let [temp__3971__auto__ {:key2 "a string"}] (if >>> temp__3971__auto__ (clojure.core/let [{key1 :key1} temp__3971__auto__] >>> true) false)) >>> >>> the consequence, IMHO, is that I would never suggest to use map >>> restructuring inside and if-let binding, because the syntax let me think >>> the result its the opposite of its semantic, >>> >>> Am I completely wrong? >>> >>> mimmo >>> >>> >>> -- >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "Clojure" group. >>> To post to this group, send email to clojure@googlegroups.com >>> Note that posts from new members are moderated - please be patient with >>> your first post. >>> To unsubscribe from this group, send email to >>> clojure+unsubscr...@googlegroups.com >>> For more options, visit this group at >>> http://groups.google.com/group/clojure?hl=en >>> --- >>> You received this message because you are subscribed to the Google Groups >>> "Clojure" group. >>> To unsubscribe from this group and stop receiving emails from it, send an >>> email to clojure+unsubscr...@googlegroups.com. >>> For more options, visit https://groups.google.com/groups/opt_out. >>> >>> >> >> >> -- >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clojure@googlegroups.com >> Note that posts from new members are moderated - please be patient with your >> first post. >> To unsubscribe from this group, send email to >> clojure+unsubscr...@googlegroups.com >> For more options, visit this group at >> http://groups.google.com/group/clojure?hl=en >> --- >> You received this message because you are subscribed to the Google Groups >> "Clojure" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to clojure+unsubscr...@googlegroups.com. >> For more options, visit https://groups.google.com/groups/opt_out. >> >> > -- -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.