Thanks, I remindered that it's a reader macro used to get the symbol
itself exactly without namespace. Ok, I see!
On 8月21日, 下午10时58分, limux <liumengji...@gmail.com> wrote:
> Is where a canonical doc about ~' or I have to read the core.clj?
>
> On 8月21日, 下午10时40分, Nicolas Oury <nicolas.o...@gmail.com> wrote:
>
>
>
>
>
>
>
> > Clojure whitin a `(...) context resolves the name space of symbols.
> > This is most often what you want and prevent some name collisions at
> > macro expension.
>
> > But as binders can not be name-space resolved this do not allow to write:
>
> > `(let [and ....])
>
> > this would expand to (let [ns/and ...]) which is forbidden.
>
> > The usual solutions (choose the first applicable) :
>
> > - use automatic name generation
> > `(let [and# ....] and#)
>
> > - generate a symbol name:
> > (let [my-fresh-sym (gensym "foo_")]
> > `(let [~my-fresh-sym ...])
>
> > It is mostly useful when the same symbols occurs in a complex
> > structure of `(...)s.
>
> > - If you really need to choose the name a binding symbol: use ~'symbol.
> > This says to the evaluation of `() "replace by exactly symbol"
> > So
> > (`let [~'and ...]) will expand to (let [and ...] ) this is a problem
> > because it can conflict with some other names.
> > However, in some case it is very useful/necessary. Especially when you
> > want to expose some symbols to the macro user.
>
> > On Sat, Aug 21, 2010 at 3:20 PM, limux <liumengji...@gmail.com> wrote:
> > > This is some code in a blog of William Gropper, the useage of ~'=
> > > confused me, waiting some more detailed explain, advanced thanks
>
> > > (defmacro filter
> > > [pred query]
> > > `(let [~'and (fn[& xs#] (apply str (interpose " AND " xs#)))
> > > ~'or (fn[& xs#] (apply str (interpose " OR " xs#)))
> > > ~'= (fn[x# y#] (sql-exp "=" x# y#))
> > > ~'> (fn[x# y#] (sql-exp ">" x# y#))
> > > ~'< (fn[x# y#] (sql-exp "<" x# y#))
> > > ~'like (fn[x# y#] (sql-exp "like" x# y#))
> > > ~'in (fn[x# xs#]
> > > (str (sqlize x#) " IN (" (apply str (interpose ", " xs#)) ")"))]
> > > (apply str ~query " where " ~pred)))
>
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