[julia-users] [Help] Julia Function does not return properly

[Sayeed Tasnim]

I'm working on some Julia code to read XDR data/files (something that might 
be generated from R using save).

I have a function read_attribute_list to read the attributes associated 
with an R Object which returns a Dict.  I also have a function read_object 
to read an R Object which calls read_attribute_list.

function read_attribute_list(rr::RReader)
  result = Dict{String,RObject}()
  typeTag = get_type_tag(rr)

  defaultRType = RType()
  while getRType(typeTag) == defaultRType.LISTSXP
    tagFlag = getTagFlag(typeTag)
    tag = None

    if tagFlag
      tag = read_symbol_or_string(rr)
    end

    car = read_object(rr)
    if car != None
      result[tag] = car
    end

    typeTag = get_type_tag(rr)

  end

  if getRType(typeTag) != defaultRType.EMPTYTAIL &&
      getRType(typeTag) != defaultRType.STRSXP
    error("Not Implemented")
  end

  return result  # result remains a Dict here and can be printed right 
before
end


function read_object(rr::RReader)
  typeTag = get_type_tag(rr)
  lengthVar = 0
  result = None
  rType = getRType(typeTag)

  defaultRType = RType()
  if rType == defaultRType.LGLSXP
    lengthVar = readInt32(rr.reader)
    boolValues = @data(bitunpack(falses(lengthVar)))
    for i in 1:lengthVar
      flag = read_integer(rr)
      if flag == 0 || flag == 1
        boolValues[i] = !(flag == 0)
      elseif flag == None
        boolValues[i] = NA
      else
        error("Invalid boolean flag from XDR: $(flag)")
      end
    end

    result = RObject(boolValues)

  elseif rType == defaultRType.INTSXP
    lengthVar = readInt32(rr.reader)
    values = @data(zeros(Int32, lengthVar))

    for i in 1:lengthVar
      value = read_integer(rr)
      if value == None
        values[i] = NA
      else
        values[i] = value
      end
    end

    result = RObject(values)

  elseif rType == defaultRType.REALSXP
    lengthVar = readInt32(rr.reader)
    values = @data(zeros(Float64, lengthVar))

    for i in 1:lengthVar
      value = readFloat64(rr.reader)
      if isnan(value)
        values[i] = NA
      else
        values[i] = value
      end
    end

    result = RObject(values)

  elseif rType == defaultRType.CPLXSXP
    lengthVar = readInt32(rr.reader)
    complexValues = @data(zeros(Complex128,lengthVar))

    for i in 1:lengthVar
      realVal = readFloat64(rr.reader)
      imaginaryVal = readFloat64(rr.reader)
      if !isnan(realVal) && !isnan(imaginaryVal)
        complexValues[i] = complex128(realVal, imaginaryVal)
      else
        complexValues[i] = NA
      end
    end

    result = RObject(complexValues)

  elseif rType == defaultRType.STRSXP
    lengthVar = readInt32(rr.reader)
    stringVector = @data(fill("", lengthVar))

    for i in 1:lengthVar
      val = read_symbol_or_string(rr)
      stringVector[i] = val != None ? val : NA
    end

    result = RObject(stringVector)

  elseif rType == defaultRType.VECSXP
    lengthVar = readInt32(rr.reader)
    vectorObject = @data(fill!(Array(Any,lengthVar),None))
    for i in 1:lengthVar
      vectorObject[i] = read_object(rr)
    end

    result = RObject(vectorObject)

  elseif rType == defaultRType.EXTPTRSXP
    readInt64(rr.reader)
    result = None

  elseif rType == defaultRType.RAWSXP
    rawLength = readInt32(rr.reader)
    result = RObject(readbytes(rr.reader, rawLength), is_raw = true)

  elseif rType == defaultRType.LANGSXP
    result = RObject(None)
    att_list = read_attribute_list(rr) # att_list returns nothing DataType
    setAttributes(result, att_list)

  elseif rType == defaultRType.SYMSXP
    symbol = read_symbol_or_string(rr)
    push!(rr.symbols, symbol)
    return RObject([symbol])

  else
    error("Unexpected type")
  end

  if getAttributeFlag(typeTag)
    att_list = read_attribute_list(rr)
    setAttributes(result, att_list)
  end

  return result
end


As read_attribute_list is called, the attributes are read correctly and the 
Dict can be viewed by printing it right before the return statement.  
However, in the highlighted code for read_object, the att_list returned is 
a nothing DataType and the Dict that was visible before is lost.

I can't figure out what would be causing this bug.  Some things that I have 
tried that might be helpful:
1) Turn off gc().  I disable garbage collection and run the code.  The 
behavior remains the same and nothing is returned.
2) Return a list of tuples instead.  Instead of returning a Dict, I return 
Array{(String,RObject)} to serialize the Dict.  The behavior remains the 
same and nothing is returned.
3) Reproduce the bug outside of the module.  I extract the part of the XDR 
file with only the attributes.  read_attribute_list reads properly and 
returns the Dict.

Feel free to ask questions about other pieces of the code or implementation 
details.  Any help with this would be appreciated!