Error Handling

Unrecoverable Errors

Exit codes terminate execution immediately:

if invalid_condition:
    exit(1)

Unhandled exceptions also become unrecoverable:

raise Exception("Critical error")  # Becomes exit(1)

UserError

User-generated errors with UTF-8 encoded messages:

# Can be caught in current sub-vm
raise gl.UserError("Invalid input")
 
# Immediate user error, more efficient but can't be caught
gl.user_error_immediate("Insufficient funds")

VMError

VM-generated errors with predefined string codes:

# Non-zero exit codes become VMError
exit(1)  # Results in VMError with specific code
 
# Resource limit violations also trigger VMError
# (handled automatically by the VM)

Catching UserError

Handle user errors from sub-VMs:

def risky_operation():
    raise gl.UserError("Operation failed")
 
try:
    result = gl.eq_principle.strict_eq(risky_operation)
except gl.UserError as e:
    print(f"Caught user error: {e.message}")

Error Propagation

Errors flow from non-deterministic to deterministic code:

def nondet_block():
    if some_condition:
        raise gl.UserError("INVALID_STATE")
    return "success"
 
try:
    gl.eq_principle.strict_eq(nondet_block)
except gl.UserError as e:
    if e.message == "INVALID_STATE":
        # Handle specific error condition
        pass

VM Result Types

GenVM produces four result types:

Return - Successful execution with encoded result
VMError - VM errors (exit codes, resource limits)
UserError - User-generated errors with UTF-8 messages
InternalError - Critical VM failures (not visible to contracts)

Storage Upgradability