Bill Allombert on Mon, 06 Aug 2012 01:00:09 +0200 |
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[a<-b,f(a)] |
Dear PARI developers, Some month ago, I have added a syntax extension [a<-b,f(a)] as a short cut for [a|a<-b,f(a)]. Unfortunately this conflicts with some valid syntax: ? [a<3] *** syntax error, unexpected integer, expecting '-': [a<3] *** ^- ? [a<-3] *** syntax error, unexpected ']', expecting ',': [a<-3] *** ^- ? [a<3,1] *** syntax error, unexpected integer, expecting '-': [a<3,1] *** ^- The origin of the problem is that '<-' is not a single token because x<-1 should be normally parsed as x < (-1), and we parse with a single token of look-ahead. Avoiding this problem was a motivation for reserving the single | sign for comprehension. But there are none in this [a<-b,f(a)] variant. So is there an alternative to [a<-b,f(a)] ? Cheers, Bill.