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Message |
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| tonyrog |
 Posted: Sun Sep 13, 2009 2:32 pm |
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User
Joined: 12 Sep 2009
Posts: 43
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mapping_form is a parse_transform that is used to construct constant mapping and reverse mapping tables.
The syntax is a bit like php arrays, the syntax accepted is:
mapping ( key1 = value1, key2 = value2 ... [ _ = default-value ] )
Where keys and values must be erlang terms.
The mapping construct returns a function that currently has three interface calls
Code:
M = mapping( a=1, b=2, c=3, d=3 ).
M(value, a). % returns 1
M(key, 3). % returns [c,d]
M(map,fun(K,V) -> {K,V} end). %% returns [{a,1},{b,2},{c,3},{d,3}]
Please send suggestions about improvements to me.
The code is totally free to use in what ever way you want. As long as you
do not blame me. |
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| tonyrog |
| Posted: Wed Sep 16, 2009 11:32 am |
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Joined: 12 Sep 2009
Posts: 43
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This update fixes issue with constant expression in keys and values. This makes mapping_form flexible when using it for defined constants using constant expressions. This update also adds optional type of mapping including:
one_to_one, one_to_many (default), many_to_one and many_to_many.
Example:
Code:
-define(A, (16#80 bor 1)).
-define(B, (16#80 bor 2)).
mapping (one_to_one, ?A = a, ?B = b ).
Syntax:
mapping ([Type,] K1=V1, .. Kn=Kv [, _=Vd ])
Where
optional Type is:
one_to_one: Both keys and values must be unique
Ki -> Vi, Vi -> Ki
one_to_many: Keys must be unique
Ki -> Vi, Vi -> [Ki,Kj..] (default)
many_to_one: Values must be unique
Ki -> [Vi,Vj,..], Vi -> Ki
many_to_many:
Ki -> [Vi,Vj,..], Vi -> [Ki,Kj,...]
The generated mapping is a function that accepts two arguments:
Mapping(value, Ki) -> Vi | [Vi,Vj..]
Mapping(key, Vi) - > Ki | [Ki,Kj..]
Mapping(map, fun(K,V) -> .. end) -> [f(K1,V1)...f(Kn,Vn)]
Ki MUST be a constant OR constant expression
Vi MUST be a constant OR constant expression OR
a mapping (reverse mapping => [])
The default mapping can only be used in
the one_to_many (default) and many_to_many mappings
The reverse mapping for the default case is not defined,
and is only used for convenience.
The reverse mapping of a mapping is not defined (yet) and
is handled as the empty list. |
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