V8 engine for knitr

R/V8engine.R

@@ -0,0 +1,46 @@
+# group source lines into complete expressions (using a brutal-force method)
+group_src_V8 = function(code, context) {
+  if ((n <- length(code)) < 1) return(list(code))
+  i = i1 = i2 = 1
+  x = list()
+  while (i2 <= n) {
+    piece = code[i1:i2]
+    if (context$validate(piece) &&  context$eval(piece)!="undefined") {
+      x[[i]] = piece; i = i + 1
+      i1 = i2 + 1 # start from the next line
+    }
+    i2 = i2 + 1
+  }
+  if (i1 <= n) parse(text = piece)  # must be an error there
+  x
+}
+
+# V8 engine - use in knitr by setting knit_engines$set(V8=V8engine)
+V8engine <- function(options) {
+  require(V8)
+  if(!exists(".context")){
+    if(is.null(options$V8.context)){
+      assign(".context", new_context(), envir = .GlobalEnv)
+    }else{
+      .context <<- options$V8.context
+    }
+    if(!is.null(options$V8.libraries)){
+      for(library in options$V8.libraries){
+        .context$source(library)
+      }
+    }
+  }
+  code <- as.character(c(options$code))
+  if(!.context$validate(code)) stop("unvalid javascript code")
+  if(!is.element(options$results, c("hide", "last"))){
+    code <- group_src_V8(code, .context)
+    output <- sapply(code, function(code) .context$eval(code))
+    code <-  sapply(code, function(code) knitr:::wrap.source(list(src= paste(code, collapse = "\n")), options))
+  }else{
+    if(options$results=="last") output <- .context$eval(code)
+    code <-  knitr:::wrap.source(list(src= paste(code, collapse = "\n")), options)
+    if(options$results=="hide") return(code)
+    return(c(code, knitr:::wrap.character(output, options)))
+  }
+  return(c(sapply(seq_along(code), function(i) c(code[i], knitr:::wrap.character(output[i], options)))))
+}