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digitalmars.D.learn - Compile time getTimes

reply "Casper =?UTF-8?B?RsOmcmdlbWFuZCI=?= <shorttail hotmail.com> writes:
I'm writing a compiler that uses Pegged for parsing D code. 
Pegged is fed a string with a special grammar syntax and changes 
it into templated D code, which is in turn mixed in. Even with 
just a small subset of D, Pegged currently produces 4000 lines of 
dense code, and it consumes enough time for it to be bothersome 
on every change, especially changes to the compiler that don't 
touch the grammar.

I wrote some simple code that uses datetime's getTimes to compare 
modification time. If grammar.d was modified more recently than 
precompiled_grammar.d, grammar.d will be churned through the 
machine once more and the result overwrite the 
precompiled_grammar.d.

However, it works only on runtime. I moved stuff around and used 
an enum for the mixin, forcing compile time function execution, 
but it whines about getTimes being unusable: "Error: 
GetFileAttributesExW cannot be interpreted at compile time, 
because it has no available source code"

Is there some hack available? Currently I run the compiler twice 
to use the past precompiled stuff or run it once and accept that 
it's slow. And this is D, so I really feel I shouldn't have to. =3
Dec 27 2013
parent "Jonathan M Davis" <jmdavisProg gmx.com> writes:
On Saturday, December 28, 2013 01:08:37 Casper Færgemand" 
<shorttail hotmail.com> puremagic.com wrote:

 I'm writing a compiler that uses Pegged for parsing D code.
 Pegged is fed a string with a special grammar syntax and changes
 it into templated D code, which is in turn mixed in. Even with
 just a small subset of D, Pegged currently produces 4000 lines of
 dense code, and it consumes enough time for it to be bothersome
 on every change, especially changes to the compiler that don't
 touch the grammar.
 
 I wrote some simple code that uses datetime's getTimes to compare
 modification time. If grammar.d was modified more recently than
 precompiled_grammar.d, grammar.d will be churned through the
 machine once more and the result overwrite the
 precompiled_grammar.d.
 
 However, it works only on runtime. I moved stuff around and used
 an enum for the mixin, forcing compile time function execution,
 but it whines about getTimes being unusable: "Error:
 GetFileAttributesExW cannot be interpreted at compile time,
 because it has no available source code"
 
 Is there some hack available? Currently I run the compiler twice
 to use the past precompiled stuff or run it once and accept that
 it's slow. And this is D, so I really feel I shouldn't have to. =3


CTFE requires that all of the source code be available (which is not the case 
with C functions) and isn't able to interact with the file system or any kind 
of I/O (beyond importing a file as a string). So, I believe that it's 
impossible to do something like check file times at compile time. You'll have 
to restrict yourself to stuff that you can do in code without any kind of I/O.

http://dlang.org/function.html#interpretation

- Jonathan M Davis
Dec 27 2013