feat: add optional history function to ProblemState

Author: AayushSabharwal

src/problem_state.jl

@@ -1,23 +1,30 @@
 """
     struct ProblemState
-    function ProblemState(; u = nothing, p = nothing, t = nothing)
+    function ProblemState(; u = nothing, p = nothing, t = nothing, h = nothing)
 
 A value provider struct which can be used as an argument to the function returned by
 [`getsym`](@ref) or [`setsym`](@ref). It stores the state vector, parameter object and
 current time, and forwards calls to [`state_values`](@ref), [`parameter_values`](@ref),
 [`current_time`](@ref), [`set_state!`](@ref), [`set_parameter!`](@ref) to the contained
 objects.
+
+A history function may be provided using the `h` keyword, which will be returned with
+[`get_history_function`](@ref).
 """
-struct ProblemState{U, P, T}
+struct ProblemState{U, P, T, H}
     u::U
     p::P
     t::T
+    h::H
 end
 
-ProblemState(; u = nothing, p = nothing, t = nothing) = ProblemState(u, p, t)
+function ProblemState(; u = nothing, p = nothing, t = nothing, h = nothing)
+    ProblemState(u, p, t, h)
+end
 
 state_values(ps::ProblemState) = ps.u
 parameter_values(ps::ProblemState) = ps.p
 current_time(ps::ProblemState) = ps.t
 set_state!(ps::ProblemState, val, idx) = set_state!(ps.u, val, idx)
 set_parameter!(ps::ProblemState, val, idx) = set_parameter!(ps.p, val, idx)
+get_history_function(ps::ProblemState) = ps.h

test/problem_state_test.jl

@@ -2,7 +2,8 @@ using SymbolicIndexingInterface
 using Test
 
 sys = SymbolCache([:x, :y, :z], [:a, :b, :c], :t)
-prob = ProblemState(; u = [1.0, 2.0, 3.0], p = [0.1, 0.2, 0.3], t = 0.5)
+prob = ProblemState(;
+    u = [1.0, 2.0, 3.0], p = [0.1, 0.2, 0.3], t = 0.5, h = Returns(ones(3)))
 
 for (i, sym) in enumerate(variable_symbols(sys))
     @test getsym(sys, sym)(prob) == prob.u[i]
@@ -13,3 +14,5 @@ end
 @test getsym(sys, :t)(prob) == prob.t
 
 @test getsym(sys, :(x + a + t))(prob) == 1.6
+
+@test get_history_function(prob) !== nothing

test/state_indexing_test.jl

@@ -347,6 +347,9 @@ getter = getsym(sys, :(x + y))
 @test getter(fs) ≈ [3.0i + 2(ts[i] - 0.1) for i in 1:11]
 @test getter(fs, 1) ≈ 2.8
 
+pstate = ProblemState(; u = u0, p = p, t = ts[1], h = t -> t .* ones(length(u0)))
+@test getter(pstate) ≈ 2.8
+
 struct TupleObservedWrapper{S}
     sys::S
 end