There's a better way to do this than a for-loop:
```lua
local WashableBlocks =
{
  [E_BLOCK_AIR] = true,
  [E_BLOCK_BROWN_MUSHROOM] = true,
  ...
}

return WashableBlocks[a_BlockType] or false
-- If your caller can survive the return values "nil" / "true",
-- then you don't even need the "or false" part of the return statement
```
Also, for performance reasons, you want to move the WashableBlocks table definition out in front of the function. Otherwise Lua will construct a new table and fill it with values each time the function is called.