Interpreter Specifications

Bytecode Interpreter

Pushes

From Reciever

When the interpreter encounters this instruction, it adds to the data stack a reference to one of the receiver's instance variables. The instance variable is specified by a single bytecode following the instruction.

From Temporary

When the interpreter encounters this instruction, it adds to the data stack a reference to one of the active context's temporary variables. The temporary variables include the message arguments. The variable is specified by a single bytecode following the
instruction.

From Literal

When the interpreter encounters this instruction, it adds to the data stack a reference to one of the method's literals. The variable is specified by a single bytecode following the instruction.

From Association

When the interpreter encounters this instruction, it adds to the data stack a reference to the "value" of an association stored in the literal frame. The association is specified by a single bytecode following the instruction.

From Special Object

When the interpreter encounters this instruction, it adds to the data stack a reference to one of the designated special objects. The object is specified by a single bytecode following the instruction accordingly: 0 - nil, 1 - true, 2 - false.

Top of Stack

When the interpreter encounters this instruction, it adds to the data stack a reference to the object currently on the top of the data stack. This duplicates the stack top.

Active Context

When the interpreter encounters this instruction, it adds to the data stack a reference to the currently active context.

Pop (&Store)

To Reciever

When the interpreter encounters this instruction, it removes the top of the data stack and stores the object in one of the receiver's instance varialbles. The instance variable is specified by a single bytecode following the instruction

To Temporary

When the interpreter encounters this instruction, it removes the top of the data stack and stores the object in one of the active context's temporary variables. The variable is specified by a single bytecode following the instruction.

To Association

When the interpreter encounters this instruction, it removes the top of the data stack and stores the object as the "value" of an association in the literal frame. The association is specified by a single bytecode following the instruction.

Top of Stack

When the interpreter encounters this instruction, it removes the top of the data stack and discards it.

Store

To Reciever

When the interpreter encounters this instruction, it stores the top of the data stack in one of the receiver's instance varialbles. The instance variable is specified by a single bytecode following the instruction

To Temporary

When the interpreter encounters this instruction, it stores the top of the data stack in one of the active context's temporary variables. The variable is specified by a single bytecode following the instruction.

To Association

When the interpreter encounters this instruction, it stores the top of the data stack as the "value" of an association in the literal frame. The association is specified by a single bytecode following the instruction.

Jump

Standard Jump

When the interpreter encounters this instruction, it advances the active context's instruction pointer by the offset embedded in the two bytecodes following the instruction. The offset must be a signed value.

If Stack Top is True

When the interpreter encounters this instruction, it pops the object off the top of the data stack. If that object is true, it advances the active context's instruction pointer by the offset embedded in the two bytecodes following the instructioin. The of
fset must be a signed value.

If Stack Top is False

When the interpreter encounters this instruction, it pops the object off the top of the data stack. If that object is false, it advances the active context's instruction pointer by the offset embedded in the two bytecodes following the instructioin. The o
ffset must be a signed value.

Send

Standard Send

When the interpreter encounters this instruction, it pops the number of arguments specified by the following bytecode off the data stack as well as a receiver. It looks up a method who's selector is stored in the literal frame and specified by the next by
tecode. If the method is found in the receiver's class or one of it's superclasses, it then composes a new context, stores the current context and makes the new context active. If it is not found it re-attempts a send using "doesNotUnderstand:" as the sel
ector and the original selector as the argument.

To Super

When the interpreter encounters this instruction, it behaves the same as when it sees a standard send; however, instead of beginning the method lookup with the receiver's class, it bypasses to the receiver's superclass.

Static

When the interpreter encounters this instruction, it behaves the same as when it sees a standard send; however, instead of looking up the method via the selector, it fetches the method from an association stored in the literal frame. The association is sp
ecified instead of the selector.

Return

From Message

When the interpreter encounters this instruction, it discards the currently active context and returns to the previous context.

From Block

When the interpreter encounters this instruction, it discards the currently active context, restores any modifications that where made to the previous context, and returns to the previous context.