here - Stefan-Marr.de

5.4. Semantics of the MOP
1 SOMObject = ( | " ... " domain | " ... "
2 postAllocate = (
3 domain := interpreter frame domain
4 initialDomainForNewObjects ) )
5
6 SOMFrame = SOMArray ( | " ... " enforced | " ... "
7 enforced = ( ^ enforced )
8 enforced : aBool = ( enforced := aBool ) )
9
10 SOMInvokable = SOMObject ( | " ... " attribute | " ... "
11 unenforced = ( ^ attribute == # unenforced ) )
12
13 SOMUniverse = ( | globals symbolTable interpreter | " ... "
14 bootstrapFrameWithArguments : args = (
15 ( interpreter pushNewFrameWithMethod : self bootstrapMethod )
16 push : ( self globalAt : # system );
17 push : args ;
18 enforced : false ) )
Listing 5.4: Structural Changes to support the OMOP in SOM
The execution of a program starts from a bootstrap frame created by the
#bootstrapFrameWithArguments: method in SOMUniverse. The initialization
of the bootstrap frame sets the execution mode to unenforced. This gives an
application the freedom to set up the runtime environment properly before
it continues with its normal execution in enforced mode. However, this also
implies that a language implementation on top of the OMOP needs to opt-in
to the enforced execution mode, which can make it prone to incorrect use by
a language implementer.
Lst. 5.5 shows the adapted implementation of the POP_FIELD bytecode. During
unenforced execution, the value that was on the top of the stack is stored
directly into the receiver. When the OMOP’s semantics are enforced however,
it triggers the intercession handler by sending #write:toField:of: to the
receiver’s domain to reify the store operation. Note that the operations of
the OMOP are executed with enforcement disabled. As shown in previous
domain definitions such as Lst. 5.1 and Lst. 5.3, the OMOP operations are annotated
with unenforced. The implementation of #pushNewFrameWithMethod
will make sure that in these cases the unenforced flag overrides normal propagation
of the enforcement flag of the frame.
Lst. 5.6 shows the corresponding read operation. It pushes the value of an
object field onto the operand stack. The main difference between POP_FIELD
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