How do I write functions that modify operations in Q#?












4














In Q#'s type documentation, it is mentioned that you can create signatures like this:



function ConjugateInvertibleWith : (inner: ((Qubit => Unit) : Adjoint),
outer : ((Qubit => Unit) : Adjoint))
: ((Qubit => Unit) : Adjoint)


My question is: how is this function actually implemented.



Presumably a function with this name will return an operation that, when invoked, calls outer, then inner, then adjoint outer. However, I have no idea how to actually write a function like this. In particular, it's not clear how to write the equivalent of a lambda with a closure. For example, if I try to declare an operation inside a function (similar to how you can def inside a def in python), I get a syntax error.



Does this have to be done in a non-Q# library, like in C#, then imported into Q#? If so, how?










share|improve this question





























    4














    In Q#'s type documentation, it is mentioned that you can create signatures like this:



    function ConjugateInvertibleWith : (inner: ((Qubit => Unit) : Adjoint),
    outer : ((Qubit => Unit) : Adjoint))
    : ((Qubit => Unit) : Adjoint)


    My question is: how is this function actually implemented.



    Presumably a function with this name will return an operation that, when invoked, calls outer, then inner, then adjoint outer. However, I have no idea how to actually write a function like this. In particular, it's not clear how to write the equivalent of a lambda with a closure. For example, if I try to declare an operation inside a function (similar to how you can def inside a def in python), I get a syntax error.



    Does this have to be done in a non-Q# library, like in C#, then imported into Q#? If so, how?










    share|improve this question



























      4












      4








      4







      In Q#'s type documentation, it is mentioned that you can create signatures like this:



      function ConjugateInvertibleWith : (inner: ((Qubit => Unit) : Adjoint),
      outer : ((Qubit => Unit) : Adjoint))
      : ((Qubit => Unit) : Adjoint)


      My question is: how is this function actually implemented.



      Presumably a function with this name will return an operation that, when invoked, calls outer, then inner, then adjoint outer. However, I have no idea how to actually write a function like this. In particular, it's not clear how to write the equivalent of a lambda with a closure. For example, if I try to declare an operation inside a function (similar to how you can def inside a def in python), I get a syntax error.



      Does this have to be done in a non-Q# library, like in C#, then imported into Q#? If so, how?










      share|improve this question















      In Q#'s type documentation, it is mentioned that you can create signatures like this:



      function ConjugateInvertibleWith : (inner: ((Qubit => Unit) : Adjoint),
      outer : ((Qubit => Unit) : Adjoint))
      : ((Qubit => Unit) : Adjoint)


      My question is: how is this function actually implemented.



      Presumably a function with this name will return an operation that, when invoked, calls outer, then inner, then adjoint outer. However, I have no idea how to actually write a function like this. In particular, it's not clear how to write the equivalent of a lambda with a closure. For example, if I try to declare an operation inside a function (similar to how you can def inside a def in python), I get a syntax error.



      Does this have to be done in a non-Q# library, like in C#, then imported into Q#? If so, how?







      programming q#






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited yesterday









      Blue

      5,67221354




      5,67221354










      asked Dec 29 '18 at 4:06









      Craig Gidney

      3,566220




      3,566220






















          1 Answer
          1






          active

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          5














          For this example, one obtains a function with that signature by partial application of an operation that is defined outside the body, instead of as a lambda in the function. As a concrete example, consider this non-generic version of the WithA operation, modified from line 73 of Q# canon.



          operation WithA(
          outer : (Qubit => Unit : Adjoint),
          inner : (Qubit => Unit : Adjoint),
          target : Qubit)
          : Unit
          {
          body (...)
          {
          outer(target);
          inner(target);
          Adjoint outer(target);
          }
          adjoint invert;
          }


          This applies the sequence $|textrm{target}ranglerightarrowtextrm{outer}^daggercdottextrm{inner}cdottextrm{outer}|textrm{target}rangle$.



          We can then partially apply the target, by using the underscore character in place of an argument, to create the desired signature as follows.



          function WithAFunction(
          outer : (Qubit => Unit : Adjoint),
          inner : (Qubit => Unit : Adjoint))
          : ((Qubit => Unit) : Adjoint)
          {
          return WithA(outer, inner, _);
          }





          share|improve this answer























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            1 Answer
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            active

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            5














            For this example, one obtains a function with that signature by partial application of an operation that is defined outside the body, instead of as a lambda in the function. As a concrete example, consider this non-generic version of the WithA operation, modified from line 73 of Q# canon.



            operation WithA(
            outer : (Qubit => Unit : Adjoint),
            inner : (Qubit => Unit : Adjoint),
            target : Qubit)
            : Unit
            {
            body (...)
            {
            outer(target);
            inner(target);
            Adjoint outer(target);
            }
            adjoint invert;
            }


            This applies the sequence $|textrm{target}ranglerightarrowtextrm{outer}^daggercdottextrm{inner}cdottextrm{outer}|textrm{target}rangle$.



            We can then partially apply the target, by using the underscore character in place of an argument, to create the desired signature as follows.



            function WithAFunction(
            outer : (Qubit => Unit : Adjoint),
            inner : (Qubit => Unit : Adjoint))
            : ((Qubit => Unit) : Adjoint)
            {
            return WithA(outer, inner, _);
            }





            share|improve this answer




























              5














              For this example, one obtains a function with that signature by partial application of an operation that is defined outside the body, instead of as a lambda in the function. As a concrete example, consider this non-generic version of the WithA operation, modified from line 73 of Q# canon.



              operation WithA(
              outer : (Qubit => Unit : Adjoint),
              inner : (Qubit => Unit : Adjoint),
              target : Qubit)
              : Unit
              {
              body (...)
              {
              outer(target);
              inner(target);
              Adjoint outer(target);
              }
              adjoint invert;
              }


              This applies the sequence $|textrm{target}ranglerightarrowtextrm{outer}^daggercdottextrm{inner}cdottextrm{outer}|textrm{target}rangle$.



              We can then partially apply the target, by using the underscore character in place of an argument, to create the desired signature as follows.



              function WithAFunction(
              outer : (Qubit => Unit : Adjoint),
              inner : (Qubit => Unit : Adjoint))
              : ((Qubit => Unit) : Adjoint)
              {
              return WithA(outer, inner, _);
              }





              share|improve this answer


























                5












                5








                5






                For this example, one obtains a function with that signature by partial application of an operation that is defined outside the body, instead of as a lambda in the function. As a concrete example, consider this non-generic version of the WithA operation, modified from line 73 of Q# canon.



                operation WithA(
                outer : (Qubit => Unit : Adjoint),
                inner : (Qubit => Unit : Adjoint),
                target : Qubit)
                : Unit
                {
                body (...)
                {
                outer(target);
                inner(target);
                Adjoint outer(target);
                }
                adjoint invert;
                }


                This applies the sequence $|textrm{target}ranglerightarrowtextrm{outer}^daggercdottextrm{inner}cdottextrm{outer}|textrm{target}rangle$.



                We can then partially apply the target, by using the underscore character in place of an argument, to create the desired signature as follows.



                function WithAFunction(
                outer : (Qubit => Unit : Adjoint),
                inner : (Qubit => Unit : Adjoint))
                : ((Qubit => Unit) : Adjoint)
                {
                return WithA(outer, inner, _);
                }





                share|improve this answer














                For this example, one obtains a function with that signature by partial application of an operation that is defined outside the body, instead of as a lambda in the function. As a concrete example, consider this non-generic version of the WithA operation, modified from line 73 of Q# canon.



                operation WithA(
                outer : (Qubit => Unit : Adjoint),
                inner : (Qubit => Unit : Adjoint),
                target : Qubit)
                : Unit
                {
                body (...)
                {
                outer(target);
                inner(target);
                Adjoint outer(target);
                }
                adjoint invert;
                }


                This applies the sequence $|textrm{target}ranglerightarrowtextrm{outer}^daggercdottextrm{inner}cdottextrm{outer}|textrm{target}rangle$.



                We can then partially apply the target, by using the underscore character in place of an argument, to create the desired signature as follows.



                function WithAFunction(
                outer : (Qubit => Unit : Adjoint),
                inner : (Qubit => Unit : Adjoint))
                : ((Qubit => Unit) : Adjoint)
                {
                return WithA(outer, inner, _);
                }






                share|improve this answer














                share|improve this answer



                share|improve this answer








                edited Dec 30 '18 at 8:58









                Craig Gidney

                3,566220




                3,566220










                answered Dec 29 '18 at 5:31









                Guang Hao Low

                1564




                1564






























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