Juan-Pablo, On Nov 10, 2007, at 6:04 PM, Juan-Pablo Caceres wrote:
A 'while(expression)' cycle will stop executing the statement as soon as the expression evaluates to 'false'. In the case of evaluating (dur => now), I think that there's also a timing logic involved, in the sense that if (1::second => now) evaluates to 'true' only when 1 second has passed, it should evaluate to false in every other time, which would cause the control to exit the block.
What (I think) is going on is that (dur => now) as an expression is just waiting, advancing time, and as soon as time has advances 'dur', it evaluates to true by default. The fact that this expression evaluates to true after the waiting time is what confuses me, compared to traditional programing language control structures.
As with the assignment operation in C and others, the specific semantics of (A => B) are that the expression evaluates to whatever the value of B is after the => part has occurred. If B happens to be 'now', chucking to it has the side effect of pausing that shred for the duration specified by A. Nothing in the control flow of a shred executes when that shred is waiting for the duration of A to pass. Additionally, keeping in mind that (A => B) evaluates to B regardless of what A and B are, if B is not zero after the chuck operation, it will evaluate to true in a conditional expression. If B happens to be 'now', it will almost always evaluate to true, the exception being at the very beginning of the ChucK virtual machine. In consequence, running this program like so: // begin 0samp.ck if( 0::samp => now ) <<< "Hello!" >>>; // end 0samp.ck $ chuck 0samp.ck produces no output, because the program runs while 'now' is still 0 (i.e. no time has passed), and thus evaluates to false in the conditional. Running this one does print something, because the program allows one sample's worth of time to pass: // begin 1samp.ck if( 1::samp => now ) <<< "Hello!" >>>; // end 1sampl.ck $ chuck 1samp.ck (Note that these examples don't work right in miniAudicle or through a chuck --loop, because the virtual machines created in those environments allow 'now' to become non-zero before any programs can run.) Though in my humble opinion, its not very clear or readable to put things like in 1::second => now in a conditional expression. Hopefully this doesn't confuse matters more... spencer
Sorry for the lengthy and confusing email! JPa.
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