I want to parse something like that :
path.to.variable
"path" and "to" are object named "Instance开发者_运维问答" and variable reference a double.
I've got the following grammar :
expr ::= instancePath:i INSTANCE_SEPARATOR SHORTCUT:s
{:
RESULT = getDouble(s);
:}
;
instancePath ::= instanceSubPath:p
{:
RESULT = p;
:}
;
instanceSubPath ::= instanceSubPath:i1 INSTANCE_SEPARATOR instanceSubPath:i2
{:
RESULT = i2;
:}
| SHORTCUT:s
{:
RESULT = pushInstance(s);
:}
;
In this grammar :
- INSTANCE_SEPARATOR is the "." char.
- SHORTCUT is a named with only letters like "path", "to" or "variable".
- expr must return a double value obtained by the call of the function getDouble which takes a name (here "variable"). This function use the current selected instance. An instance contains a hashtable which contains double or other instance.
- pushInstance is a function which set the current instance
for example we could have :
- an instance "path" which contains a hashtable which is : "to"=>link to instance "to"
- an instance "to" which contains a hashtable which is : "variable"=>10
- the path "path.to.variable" must return 10.
This does not run because the grammar complains a null value. This is due to the fact the parser does this :
expr(
instancePath(
instanceSubPath(SHORTCUT("path"))
INSTANCE_SEPARATOR
instanceSubPath(SHORTCUT("to"))
INSTANCE_SEPARATOR
instanceSubPath(SHORTCUT("variable"))
)
INSTANCE_SEPARATOR
!NULL!
)
instead of doing
expr(
instancePath(
instanceSubPath(SHORTCUT("path"))
INSTANCE_SEPARATOR
instanceSubPath(SHORTCUT("to"))
)
INSTANCE_SEPARATOR
SHORTCUT("variable")
)
Why ? is there precedence problems ?
To finish, if I remove the instancePath rule, all runs :
expr ::= instanceSubPath:i INSTANCE_SEPARATOR SHORTCUT:s
{:
RESULT = getDouble(s);
:}
;
instanceSubPath ::= instanceSubPath:i1 INSTANCE_SEPARATOR instanceSubPath:i2
{:
RESULT = i2;
:}
| SHORTCUT:s
{:
RESULT = pushInstance(s);
:}
;
I can't remove this extra rules because I've simplified the example but it's quite more complex in reality.
I don't understand why deleting this extra rule solve my problem...
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