Add callback types and function stubs

src/CryoGrid.jl

@@ -9,14 +9,14 @@ end
 using Base: @propagate_inbounds
 using Reexport
 
+# Common types and methods
 export Layer, SubSurface, Top, Bottom
 export Process, SubSurfaceProcess, BoundaryProcess, CompoundProcess, Coupled
 export BoundaryStyle, Dirichlet, Neumann
-export AbstractParameterization, Parameterization
-export variables, initialcondition!, diagnosticstep!, prognosticstep!, interact!, boundaryflux, boundaryvalue, observe
-
-# Common types and methods
+export Callback, CallbackStyle
 include("types.jl")
+export variables, initialcondition!, diagnosticstep!, prognosticstep!, interact!
+export boundaryflux, boundaryvalue, criterion, affect!, observe
 include("methods.jl")
 
 # Submodules

src/methods.jl

 """
     variables(::Layer, ::Process)
 
-Defines variables for a given Process on Layer. Implementations should return a `Tuple` of `Var`s.
+Defines variables for a given Process on the given Layer. Implementations should return a `Tuple` of `Var`s.
 """
 variables(::Layer, ::Process) = ()
+"""
+    callbacks(::Layer, ::Process)
+
+Defines callbacks for a given Process on the given Layer. Implementations should return a `Tuple` or `Callback`s.
+"""
+callbacks(::Layer, ::Process) = ()
 """
     initialcondition!(::Layer, ::Process, state)
 
-Defines the initial condition for a given Process on Layer. `initialcondition!` should write initial values into all relevant
+Defines the initial condition for a given Process on the given Layer. `initialcondition!` should write initial values into all relevant
 state variables in `state`.
 """
 initialcondition!(::Layer, ::Process, state) = nothing
@@ -53,6 +59,18 @@ boundaryflux(s::BoundaryStyle, bc::BoundaryProcess, b::Union{Top,Bottom}, p::Sub
 Computes the value of the boundary condition specified by `bc` for the given layer/process combinations.
 """
 boundaryvalue(bc::BoundaryProcess, b, p, layer, sbc, ssub) = error("missing implementation of boundaryvalue for $(typeof(b)) $(typeof(bc)) on $(typeof(layer)) with $(typeof(p))")
+"""
+    criterion(c::Callback, ::Layer, ::Process, state)
+
+Callback criterion/condition. Should return a `Bool` for discrete callbacks and a real number for continuous callbacks.
+"""
+criterion(c::Callback, ::Layer, ::Process, state) = error("missing implementation of criterion for $(typeof(c))")
+"""
+    affect!(c::Callback, ::Layer, ::Process, state)
+
+Callback action executed when `criterion` is met (boolean condition for discrete callbacks, zero for continuous callbacks).
+"""
+affect!(c::Callback, ::Layer, ::Process, state) = error("missing implementation of affect! for $(typeof(c))")
 """
     observe(::Val{name}, ::Layer, ::Process, state1)
 
@@ -86,3 +104,5 @@ where `BP` is a `BoundaryProcess` that provides the boundary conditions.
 """
 BoundaryStyle(::Type{BP}) where {BP<:BoundaryProcess} = error("No style specified for boundary process $BP")
 BoundaryStyle(bc::BoundaryProcess) = BoundaryStyle(typeof(bc))
+# default callback style impl
+CallbackStyle(::Type{<:Callback}) = Discrete()

src/types.jl

@@ -88,3 +88,17 @@ struct Dirichlet <: BoundaryStyle end
 `BoundaryStyle` instance for Neumann boundary conditions.
 """
 struct Neumann <: BoundaryStyle end
+"""
+    Callback
+
+Base type for callback implementations.
+"""
+abstract type Callback end
+"""
+    CallbackStyle
+
+Trait for callback types.
+"""
+abstract type CallbackStyle end
+struct Discrete <: CallbackStyle end
+struct Continuous <: CallbackStyle end