Parsing line-based structure (ray tracer) without using too many vars - parsing

Question

I want to parse a file in scala (probably using JavaTokerParsers?). Possibly without using too many vars :-)
The file is the input for a ray tracer.
It is a line based file structure.
Three types of lines exists: empty line, comment line and command line
The comment line starts with # (maybe has some whitespace before the #)
Command line starts with an identifier optionally followed by a number of parameters (float or filename).
How would I go about this. I would want to parser to be called like this
val scene = parseAll(sceneFile, file);
Sample file:
#Cornell Box
size 640 480
camera 0 0 1 0 0 -1 0 1 0 45
output scene6.png
maxdepth 5
maxverts 12
#planar face
vertex -1 +1 0
vertex -1 -1 0
vertex +1 -1 0
vertex +1 +1 0
#cube
vertex -1 +1 +1
vertex +1 +1 +1
vertex -1 -1 +1
vertex +1 -1 +1
vertex -1 +1 -1
vertex +1 +1 -1
vertex -1 -1 -1
vertex +1 -1 -1
ambient 0 0 0
specular 0 0 0
shininess 1
emission 0 0 0
diffuse 0 0 0
attenuation 1 0.1 0.05
point 0 0.44 -1.5 0.8 0.8 0.8
directional 0 1 -1 0.2 0.2 0.2
diffuse 0 0 1
#sphere 0 0.8 -1.5 0.1
pushTransform
#red
pushTransform
translate 0 0 -3
rotate 0 1 0 60
scale 10 10 1
diffuse 1 0 0
tri 0 1 2
tri 0 2 3
popTransform
#green
pushTransform
translate 0 0 -3
rotate 0 1 0 -60
scale 10 10 1
diffuse 0 1 0
tri 0 1 2
tri 0 2 3
popTransform
#back
pushTransform
scale 10 10 1
translate 0 0 -2
diffuse 1 1 1
tri 0 1 2
tri 0 2 3
popTransform
#sphere
diffuse 0.7 0.5 0.2
specular 0.2 0.2 0.2
pushTransform
translate 0 -0.7 -1.5
scale 0.1 0.1 0.1
sphere 0 0 0 1
popTransform
#cube
diffuse 0.5 0.7 0.2
specular 0.2 0.2 0.2
pushTransform
translate -0.25 -0.4 -1.8
rotate 0 1 0 15
scale 0.25 0.4 0.2
diffuse 1 1 1
tri 4 6 5
tri 6 7 5
tri 4 5 8
tri 5 9 8
tri 7 9 5
tri 7 11 9
tri 4 8 10
tri 4 10 6
tri 6 10 11
tri 6 11 7
tri 10 8 9
tri 10 9 11
popTransform
popTransform
popTransform

Answer 1

Maybe I've pushed it too hard for the one liner but that's my take (although idiomatic it might not be optimal):
First, CommandParams represents a command along with its arguments in a list format. If no arguments then we have None args:
case class CommandParams(command:String, params:Option[List[String]])
Then here's the file parsing and construction one liner along with line-by-line explanation:
val fileToDataStructure = Source.fromFile("file.txt").getLines() //open file and get lines iterator
.filter(!_.isEmpty) //exclude empty lines
.filter(!_.startsWith("#")) //exclude comments
.foldLeft(List[CommandParams]()) //iterate and store in a list of CommandParams
{(listCmds:List[CommandParams], line:String) => //tuple of a list of objs so far and the current line
val arr = line.split("\\s") //split line on any space delim
val command = arr.head //first element of array is the command
val args = if(arr.tail.isEmpty) None else Option(arr.tail.toList) //rest are their params
new CommandParams(command, args)::listCmds //construct the obj and cons it to the list
}
.reverse //due to cons concat we need to reverse to preserve order
A demo output iterating through it:
fileToDataStructure.foreach(println)
yields:
CommandParams(size,Some(List(640, 480)))
CommandParams(camera,Some(List(0, 0, 1, 0, 0, -1, 0, 1, 0, 45)))
CommandParams(output,Some(List(scene6.png)))
CommandParams(maxdepth,Some(List(5)))
CommandParams(maxverts,Some(List(12)))
CommandParams(vertex,Some(List(-1, +1, 0)))
...
CommandParams(pushTransform,None)
CommandParams(pushTransform,None)
CommandParams(translate,Some(List(0, 0, -3)))
...
A demo of how to iterate through it to do actual work once loaded:
fileToDataStructure.foreach{
cmdParms => cmdParms match {
case CommandParams(cmd, None) => println(s"I'm a ${cmd} with no args")
case CommandParams(cmd, Some(args))=> println(s"I'm a ${cmd} with args: ${args.mkString(",")}")
}
}
yields output:
I'm a size with args: 640,480
I'm a camera with args: 0,0,1,0,0,-1,0,1,0,45
I'm a output with args: scene6.png
I'm a maxdepth with args: 5
I'm a maxverts with args: 12
I'm a vertex with args: -1,+1,0
...
I'm a popTransform with no args
I'm a popTransform with no args