You need to distinguish between "compiled" and "aot compiled to byte
code".
As far as I know, all forms are compiled before they are executed. So,
if you type:
(+ 1 1)
it is first compiled to bytecode, and then run. It's not executed at
compile time at all; rather when it is evaluated, it is compiled and
then run. If you aot compile, then you are do the same thing, but dump
the bytecode to file. So, you still evaluate the entire top level.
So, when you say compile, I presume you you mean aot compiled. Macros
have to be run, so the question is should they be expanded but not
evaluated? And what about macros with side-effects?
And if top level forms are NOT evaluated when loaded what would this do:
(ns user)
(def x 1)
(load "user_y")
=== in user_y.clj
(def y 1)
Now the AOT would only load the first file in the namespace because
(load "user_y") would not be evaluated.
Why are you worried about this? Most of the time compilation in Clojure
is an implementation detail, as it is in python. It just happens when it
needs to, and away you go.
Phil
Andrew Chambers <andrewchambe...@gmail.com> writes:
> Why are the toplevel forms which arent macros executed at compile time? For
> example Lua can be compiled to bytecode without executing
> its top level calls.
>
>
> On Tue, Apr 15, 2014 at 9:04 PM, Softaddicts
> <lprefonta...@softaddicts.ca>wrote:
>
>> Ahem :)
>>
>> a) The fn x does not exist in the universe until you call foo, hence you
>> cannot
>> expect the compiler to known anything about it if it's not called
>> before
>> making any reference to x.
>>
>> b) If you refer to x at the top level (the "universe" above :) before
>> defining
>> it, obviously it does not exist. You might use (declare x) before
>> referring to it. This allows you to define it later at your
>> convenience.
>>
>> c) In general, you should avoid using def/defn within a function.
>> Macros may do that but this is a different story.
>>
>> d) Yes code at the top level is executed, how can you expect
>> the REPL to work interactively if forms are not evaluated first ?
>> A defn expands to a function call, a special form in fact but it still
>> behaves
>> like a function. Any function call at top level will get executed
>> after being
>> compiled to byte code.
>>
>> Now about the "compilation" step...
>>
>> Traditionally, most Lisps allow you to refer to stuff in interpreted mode
>> not defined yet hoping that it will get defined by the time you run the
>> code
>> that refers to these undefined things. It can even be something transient
>> on
>> the stack... oups...
>>
>> You can still compile in other Lisps but this is a special case where you
>> have to
>> make sure that stuff is defined in some way. You need to add directives to
>> tell the compiler that this stuff will exist later and that it can safely
>> refer to it.
>>
>> On the JVM, some underlying byte code has to be generated for any forms
>> typed in the REPL at the top level any reference has to be defined before
>> hand.
>>
>> There's no other way to generate byte code... there cannot be black holes
>> waiting to get filled later.
>>
>> Hence the "compilation" phase and the restriction
>> that stuff you refer to are to be defined either directly or using declare.
>>
>> Hope it explains the compromise.
>>
>> Luc P.
>>
>>
>> > Is there an explanation of how clojure deals with scoping and its static
>> > checking. It seems to be a hybrid of a static language and a dynamic
>> > language when it comes to compilation. I'll elaborate.
>> >
>> > The following code wont compile:
>> > (defn x [] nil)
>> > (defn y[]) ((x))
>> >
>> > however this code will compile:
>> >
>> > (defn foo[] (defn x[] nil))
>> > (defn y[]) ((x))
>> >
>> > but calling y before foo fails with a runtime exception.
>> >
>> > Also, the following code:
>> >
>> > (println "hello")
>> > (defn -main [args]
>> > (println "world"))
>> >
>> > prints "hello" at compile time
>> > and also
>> > "hello
>> > world" at runtime.
>> >
>> > My conclusions from this is that the static symbol checker is actually
>> > fairly stupid and is just there to provide some simple sanity, and that
>> all
>> > toplevel code in a namespace
>> > is executed at compile time AND at runtime. Is this correct?
>> >
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>> Softaddicts<lprefonta...@softaddicts.ca> sent by ibisMail from my ipad!
>>
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--
Phillip Lord, Phone: +44 (0) 191 222 7827
Lecturer in Bioinformatics, Email: phillip.l...@newcastle.ac.uk
School of Computing Science,
http://homepages.cs.ncl.ac.uk/phillip.lord
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