Determining a recipe's "learnability."

[zachwlewis]

I've an addon that currently will look through a merchant's inventory and tell the user how many recipes he has. I'd also like it to list how many recipes he has that are currently learnable.

I tried using the function IsUsableItem(itemLink), but that function returns true for any recipe I currently have in my inventory (which, technically, is usable, I suppose). What function should I be using to determine an item's "learnability?" The more information I can get, the better.

Here's my current merchant search:

function checkMerchantInventory()
  local itemCount = GetMerchantNumItems()
  local recipeCount = 0
  local usableCount = 0
  for i=1,itemCount do
    -- Our current item.
    local currentItem = GetMerchantItemLink(i)
    if (currentItem == nil) then
      scanSuccessful = false
      return
    end
    
    -- Get assorted information about the item.
    local name, link, quality, iLevel, reqLevel, class, subclass, maxStack, equipSlot, texture, vendorPrice = GetItemInfo(currentItem)
 
    if (class == "Recipe") then
      recipeCount = recipeCount + 1
 
      -- Get usability information about the item.
      local isUsable = IsUsableItem(currentItem)
      if (isUsable) then
        usableCount = usableCount + 1
        print(currentItem)
      end
    end
  end
  
  -- Search output
  if recipeCount > 0 then
    print("|cFFFF6666 Look! New Recipe!|r "..recipeCount.." recipes, of which "..usableCount.." are useable.")
    PlaySoundFile("Sound/Creature/Cat/CatStepA.ogg")
  else
    print("|cFFFF9999 No new recipes found.|r")
  end
 
  scanSuccessful = true
end