Skip to main content

​
Classical Control Flow

Loops and conditionals on classical expressions are useful means to describe reusable building blocks. Qmod has two basic forms - the repeat statement and the if statement.

​
Classical Repeat

​
Syntax

def repeat(count: CInt, iteration: QCallable[CInt]) -> None:
    pass

​
Semantics

  • Invoke the iteration block count times, binding the index variable to the respective iteration number - 0, 1,… count-1.
  • Inside the statement block, use of quantum variables declared outside it is restricted to contexts where the variable is initialized and remains initialized (see Quantum Variables)

​
Example

The following example defines a useful function - applying the Hadamard function across all qubits in a qubit array - using repeat. Note that a similar function is available in the Classiq open-library. 
from classiq import H, QArray, QBit, qfunc, repeat


@qfunc
def my_hadamard_transform(qba: QArray[QBit]):
    repeat(
        count=qba.len,
        iteration=lambda index: H(qba[index]),
    )

​
Classical If

​
Syntax

def if_(condition: CBool, then: QCallable, else_: Optional[QCallable] = None) -> None:
    pass
Note that identifiers in Qmod that happen to conflict with Python keywords have _ suffix. This is the case with if_ and else_ in the second function.

​
Semantics

  • Invoke the then block if condition evaluates to true and otherwise invoke the else block
  • Inside the statement block, use of quantum variables declared outside it is restricted to contexts where the variable is initialized and remains initialized (see Quantum Variables)

​
Example

from classiq import CBool, X, Y, QBit, qfunc, if_


@qfunc
def my_conditional_gate(cond: CBool, qb: QBit):
    if_(
        condition=cond,
        then=lambda _: X(qb),
        else_=lambda _: Y(qb),
    )