Re: [Yaml-core] Tutorial Plans and Current Version (Types in prog ress)

[Clark C . E. <cc...@cl...>]

Ok.  There isn't a nice way to do this; I withdraw
the suggestion.  Anchors work "dumb" mode.

Clark

On Sat, Nov 17, 2001 at 05:17:17PM -0500, Clark C . Evans wrote:
| | > And anchors may shadow previous 
| | > anchors for aliases at the same level of indentation or higher. This 
| | > shadowing policy allows for simple, cut, indent, and paste. 
| | 
| | I doubt it is that simple:
| | 
| | a0:
| |  b0: &001
| |   c0: &002 ...
| | a1: *001
| | a2: *002
| | a3:
| |  b1: &002 shadows it...
| |   c1: &001 shadows it...
| | 
| | You can't get away with "level" tricks here.
| 
| It's ugly... but here is a first pass (a sparse
| list would be nice)... written but not tested.
| The goal is to have each anchor be a mapping
| to a list of values that are relevant depending
| on your level.  Efficient it isn't.  But I'm
| sure with some mental work this could be a
| fairly quick operation.  In the "best" case
| when anchors are never reused, it is only a
| tiny bit slower (a tuple is used).  However,
| on the shadow cases, an entire list of values
| indexed by level is required.
| 
| ...
| 
| import types
| anchors = {}
| 
| def set_list(lst,lvl,val):
|     # poor man's sparse list
|     # make sure list is big enough,
|     # lvl is 1,2,3,4
|     diff = lvl - len(lst)
|     if diff > 0: lst.extend((None,)*diff)
|     lst[lvl-1] = val
|     return lst[:lvl]
| 
|     
| def get_list(lst,lvl):
|     # return most specific value
|     # for the given level
|     ret = None
|     idx = 0
|     while idx < len(lst):
|         if idx > (lvl-1):
|             if ret:
|                 return ret
|         ret = lst[idx]
|     return ret
|     
| def set(lvl,key,val):
|     cur = anchors.get(key,None)
|     if cur:
|         if type(cur) is types.ListType:
|             # if it is a list already
|             anchors.set(key,set_list(cur,lvl,val))            
|         else:
|             # if it is a scalar
|             (old_lvl,old_val) = cur
|             if old_val >= lvl:
|                 # update the scalar
|                 anchors.set(key,(lvl,val))
|             else
|                 # we need to make a list
|                 anchors.set(key,
|                     set_list(
|                         set_list([],lvl,val),
|                         old_lvl, old_val))
|     else:
|         # brand new value
|         anchors.set(key,(lvl,val))
| 
| def get(lvl,key):
|     ret = None
|     cur = anchors.get(key,None)    
|     if cur:
|         if type(cur) is types.ListType:
|              ret = get_list(cur,lvl)
|         else:
|              ret = cur[1]
|     return ret
|             
|         
| 
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-- 
Clark C. Evans                   Axista, Inc.
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