migrate express functionality to QuantumInterface

src/QSymbolicsBase/QSymbolicsBase.jl

@@ -16,7 +16,8 @@ import QuantumInterface:
     basis,Basis,samebases,IncompatibleBases,SpinBasis,FockBasis,CompositeBasis,
     nqubits,
     projector,dagger,tr,ptrace,
-    AbstractBra,AbstractKet,AbstractOperator,AbstractSuperOperator
+    AbstractBra,AbstractKet,AbstractOperator,AbstractSuperOperator,
+    express,AbstractRepresentation,QuantumOpticsRepr,QuantumMCRepr,CliffordRepr
 
 export SymQObj,QObj,
        AbstractRepresentation,AbstractUse,
@@ -53,8 +54,6 @@ export SymQObj,QObj,
 # Metadata cache helpers
 ##
 
-"""An abstract type for the supported representation of quantum objects."""
-abstract type AbstractRepresentation end
 abstract type AbstractUse end
 struct UseAsState <: AbstractUse end
 struct UseAsOperation <: AbstractUse end

src/QSymbolicsBase/express.jl

@@ -37,8 +37,6 @@ julia> express(QuantumSymbolics.X, CliffordRepr(), UseAsObservable())
 + X
 ```
 """
-function express end
-
 function express(state::Symbolic, repr::AbstractRepresentation, use::AbstractUse)
     md = metadata(state)
     isnothing(md) && return express_from_cache(express_nolookup(state, repr, use))
@@ -72,28 +70,13 @@ function consistent_representation(reprs,state)
     end
     first(reprs)
 end
-
-##
-# Commonly used representations -- interfaces for each one defined in separate packages
-##
-
-"""Representation using kets, bras, density matrices, and superoperators governed by `QuantumOptics.jl`."""
-@kwdef struct QuantumOpticsRepr <: AbstractRepresentation 
-    cutoff::Int = 2
-end
-"""Similar to `QuantumOpticsRepr`, but using trajectories instead of superoperators."""
-struct QuantumMCRepr <: AbstractRepresentation end
-"""Representation using tableaux governed by `QuantumClifford.jl`"""
-struct CliffordRepr <: AbstractRepresentation end
-
 express(state::Symbolic) = express(state, QuantumOpticsRepr()) # The default representation
 express_nolookup(state, ::QuantumMCRepr) = express_nolookup(state, QuantumOpticsRepr())
-express(state) = state
 
 function express_nolookup(s, repr::AbstractRepresentation)
     if isexpr(s)
         operation(s)(express.(arguments(s), (repr,))...)
     else
         error("Encountered an object $(s) of type $(typeof(s)) that can not be converted to $(repr) representation") # TODO make a nice error type
     end
-end
+end