Better way of extracting string from expression #35

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1. wch commented on Nov 11, 2016

   

   wch

   on Nov 11, 2016

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   Note that attr(src_1, "srcfile")$lines gives a string with \n characters in it instead of a char vector where each element represents one line. Running the code in the above example has someNAs:

   lines
   # [1] "\n  # This is a comment\n  a +      b\n})\n"
   # [2] NA                                           
   # [3] NA  

   So you need to add a strsplit():

   x <- quote({
     # This is a comment
     a +      b
   })
   
   src <- attr(x, "srcref")
   src_1 <- src[[1]]
   src_n <- src[[length(src)]]
   
   lines <-  attr(src_1, "srcfile")$lines
   lines <-  strsplit(lines, "\n")[[1]]     # <-- Here
   lines <- lines[seq(src_1[1], src_n[3])]
   lines[1] <- substring(lines[1], src_1[5] + 1, nchar(lines[1]))
   
   if (lines[1] == "" || grepl("^\\s+$", lines[1])) {
     lines <- lines[-1]
   }
   lines
   # [1] "  # This is a comment" "  a +      b"         

   Oddly, if you access the source ref before the lines, it causes the string to be split up into a char vector, as a side effect -- just like if you called strsplit() on it.

   x <- quote({
     # This is a comment
     a +      b
   })
   
   src <- attr(x, "srcref")
   src_1 <- src[[1]]
   src_n <- src[[length(src)]]
   
   srcref(attr(src_1, "srcfile"), c(1,1,1,1,1,1,1,1))  # <--- Here
   lines <-  attr(src_1, "srcfile")$lines
   lines <- lines[seq(src_1[1], src_n[3])]
   lines[1] <- substring(lines[1], src_1[5] + 1, nchar(lines[1]))
   
   if (lines[1] == "" || grepl("^\\s+$", lines[1])) {
     lines <- lines[-1]
   }
   lines
   # [1] "  # This is a comment" "  a +      b"         
2. jennybc commented on Nov 11, 2016

   

   jennybc

   on Nov 11, 2016

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   It appears that attr(src[[1]], "srcfile")$fixedNewlines can be consulted to determine the split status.
3. jennybc

   added a commit that references this issue on Nov 12, 2016

   implement expression processing suggested in #35; closes #35

   0271b9a
4. jennybc

   closed this as completedin 0271b9aon Nov 12, 2016