 # Change a function without the actual evaluation ...?

Hi.

I’d like to know if there is a way to convert a function to a different form without the actual evaluation.

For example, I’m trying to make an API of DifferentialEquations.jl. However, I encountered a serious performance degradation. The following code is an example of my API.

``````function DifferentialEquations.ODEProblem(env::AbstractEnv, f, x0, tspan; kwargs...)
warn_is_registered(env)
_x0 = raw(env, x0)
_f(_x, p, t) = raw(env, f(readable(env, _x), p, t))
ODEProblem(_f, _x0, tspan; kwargs...)
end
``````

In the above code, `x0` denotes NamedTuple-valued (i.e., readable) initial condition.
`_x0` is a vector-valued (i.e., raw) initial condition.
From this line, `_f(_x, p, t) = raw(env, f(readable(env, _x), p, t))`, you may notice that the argument `f` of the extended function `DifferentialEquations.ODEProblem(env::AbstractEnv, f, x0, tspan; kwargs...)` will receive a “readable” state (`x`) and provide a “readable” output of its derivative.
For the compatibility with DifferentialEquations.jl, `_f`, which is the injected dynamical equations into `ODEProblem` provided by DifferentialEquations.jl, should provide a “raw” output, so the output of `f(readable(env, _x), p, t)` is wrapped by `raw`.

In this case, I realised that every call of `_f` would require two processings, `raw` and `readable`, which drastically degrade the performance. So, I wonder if there is a way of parsing the “readable” dynamical equations, `f`, to the “raw” dynamical equations, `_f`, at the beginning, not every time it is called.

LabelledArrays.jl resolves my issue. So I closed this conversation.

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