Understanding Parse Trees

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The latest version of this topic can be found at ATL Registrar and Parse Trees.

You can define one or more parse trees in your registrar script, where each parse tree has the following form:

<root key>{<registry expression>}+  

where:

<root key> ::= HKEY_CLASSES_ROOT | HKEY_CURRENT_USER |  
    HKEY_LOCAL_MACHINE | HKEY_USERS |  
    HKEY_PERFORMANCE_DATA | HKEY_DYN_DATA |  
    HKEY_CURRENT_CONFIG | HKCR | HKCU |  
    HKLM | HKU | HKPD | HKDD | HKCC  
<registry expression> ::= <Add Key> | <Delete Key>  
<Add Key> ::= [ForceRemove | NoRemove | val]<Key Name>  
 [<Key Value>][{<Add Key>}]  
<Delete Key> ::= Delete<Key Name>  
<Key Name> ::= '<AlphaNumeric>+'  
<AlphaNumeric> ::= any character not NULL, i.e. ASCII 0  
<Key Value> ::== <Key Type><Key Name>  
<Key Type> ::= s | d  
<Key Value> ::= '<AlphaNumeric>'  

A parse tree can add multiple keys and subkeys to the <root key>. In doing so, it keeps a subkey's handle open until the parser has completed parsing all of its subkeys. This approach is more efficient than operating on a single key at a time, as seen in the following example:

HKEY_CLASSES_ROOT  
{  
 'MyVeryOwnKey'  
 {  
 'HasASubKey'  
 {  
 'PrettyCool'  
 }  
 }  
}  

Here, the Registrar initially opens (creates) HKEY_CLASSES_ROOT\MyVeryOwnKey. It then sees that MyVeryOwnKey has a subkey. Rather than close the key to MyVeryOwnKey, the Registrar retains the handle and opens (creates) HasASubKey using this parent handle. (The system registry can be slower when no parent handle is open.) Thus, opening HKEY_CLASSES_ROOT\MyVeryOwnKey and then opening HasASubKey with MyVeryOwnKey as the parent is faster than opening MyVeryOwnKey, closing MyVeryOwnKey, and then opening MyVeryOwnKey\HasASubKey.

See Also

Creating Registrar Scripts