- v <- "((2-x^2+3)^2+(x-5+7)^10)^0.5" 
- x <- grepl("(\\(((?:[^()]++|(?1))*)\\))\\^(\\d*\\.?\\d+)", v, perl=TRUE) 
- while(x) { 
- 	v <- sub("(\\(((?:[^()]++|(?1))*)\\))\\^(\\d*\\.?\\d+)", "pow(\\2, \\3)", v, perl=TRUE); 
- 	x = grepl("(\\(((?:[^()]++|(?1))*)\\))\\^(\\d*\\.?\\d+)", v, perl=TRUE) 
- } 
- v 
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