LOAD Instruction - craterdog-archives/js-bali-virtual-machine GitHub Wiki

The LOAD Instruction

The LOAD instruction causes a component to be retrieved from the cloud environment and loaded onto the component stack. The source of the component depends on the specified modifier:

• VARIABLE
• DOCUMENT
• CONTRACT
• MESSAGE

The operand contains an index value in the range 1..2047 of the variable that specifies the source of the component.

LOAD VARIABLE variable

The LOAD instruction with a VARIABLE modifier loads, onto the component stack, the value that is currently saved in the variable identified by the variable operand. The bytecode for this instruction has the form:

[01100xxx][xxxxxxxx] where xxxxxxxxxxx is the index of the variable containing the component

The following pseudo-code defines this instruction:

variable = context.variables.get(context.operand)
task.components.push(variable)
context.address = context.address + 1

Example Context Before Execution

Example Context After Execution

LOAD DOCUMENT citation

The LOAD instruction with a DOCUMENT modifier loads, onto the component stack, the document whose citation is saved in the variable identified by the citation operand. The bytecode for this instruction has the form:

[01101xxx][xxxxxxxx] where xxxxxxxxxxx is the index of the variable containing the citation to the document

The following pseudo-code defines this instruction:

citation = context.variables.get(context.operand)
document = repository.retrieveDocument(citation)
task.components.push(document)
context.address = context.address + 1

Example Context Before Execution

Example Context After Execution

LOAD CONTRACT name

The LOAD instruction with a CONTRACT modifier loads, onto the component stack, the contract whose name is saved in the variable identified by the name operand. The bytecode for this instruction has the form:

[01110xxx][xxxxxxxx] where xxxxxxxxxxx is the index of the variable containing the name of the contract

The following pseudo-code defines this instruction:

name = context.variables.get(context.operand)
contract = repository.retrieveContract(name)
task.components.push(contract)
context.address = context.address + 1

Example Context Before Execution

Example Context After Execution

LOAD MESSAGE bag

The LOAD instruction with a MESSAGE modifier loads, onto the component stack, a message randomly chosen from the message bag whose name is saved in the variable identified by the bag operand. The bytecode for this instruction has the form:

[01111xxx][xxxxxxxx] where xxxxxxxxxxx is the index of the variable containing the name of the bag

The following pseudo-code defines this instruction:

bag = context.variables.get(context.operand)
message = repository.retrieveMessage(bag)
if message then {
    -- the bag contained a message
    task.components.push(message)
    context.address = context.address + 1
} else {
    -- the bag was empty, need to retry this instruction again later
    repository.postMessage('/bali/vm/tasks/v1', task)
    task.status = $paused
}

Example Context Before Execution

Example Context After Execution