I need a macro that takes any expression matching r"-?[0-9]+\Q.\E[0-9]+", and encloses it in a BigFloat constructor. For example, a macro that receives the source code below:

@my_macro function f()
sum = 0.0
x = 902.4
y = -47.1
for i in 1:20
sum += x^2 + 4.3*y
end
return sum
end

and returns the following:

function f()
sum = BigFloat("0.0")
x = BigFloat("902.4")
y = BigFloat("-47.1")
for i in 1:20
sum += x^2 + BigFloat("4.3")*y
end
return sum
end

julia> expr = quote
function f()
sum = 0.0
x = 902.4
y = -47.1
for i in 1:20
sum += x^2 + 4.3*y
end
return sum
end
end;
julia> using MacroTools: postwalk
julia> postwalk(x -> x isa Float64 ? Expr(:call, :BigFloat, string(x)) : x, expr)
quote
#= REPL[13]:2 =#
function f()
#= REPL[13]:3 =#
sum = BigFloat("0.0")
#= REPL[13]:4 =#
x = BigFloat("902.4")
#= REPL[13]:5 =#
y = BigFloat("-47.1")
#= REPL[13]:6 =#
for i = 1:20
#= REPL[13]:7 =#
sum += x ^ 2 + BigFloat("4.3") * y
end
#= REPL[13]:9 =#
return sum
end
end

You would just need to write a macro that calls postwalk on its input.

I tried to download the package, but got an error:

(@v1.4) pkg> add https://github.com/stevengj/ChangePrecision.jl
Updating git-repo `https://github.com/stevengj/ChangePrecision.jl`
ERROR: could not find project file in package at https://github.com/stevengj/ChangePrecision.jl

julia> using MacroTools: postwalk
julia> macro big_float_precision(expr)
return postwalk(x -> x isa Float64 ? Expr(:call, :BigFloat, string(x)) : x, expr)
end
@big_float_precision (macro with 1 method)
julia> @big_float_precision function f()
sum = 0.0
x = 902.4
y = -47.1
for i in 1:20
sum += x^2 + 4.3*y
end
return sum
end
f (generic function with 1 method)
julia> typeof(f())
BigFloat