Use Cassette and ReplMaker to create REPL that has deterministic rand()

RandAlwaysHalf.jl

# Based on https://gist.github.com/mbauman/d0c27f40e25393ef050b87b4bb6a69dc

using Cassette, ReplMaker

Cassette.@context RandAlwaysHalf

randreturnshalf(s, x) = x
function randreturnshalf(s, f, fx)
  if f == rand
    return randreturnshalf(s, one(typeof(fx)) / 2)
  else
    return fx
  end
end

Cassette.overdub(::RandAlwaysHalf, f, args...) = randreturnshalf("$f$args", f, f(args...))

function parse_to_expr(s)
    p = Meta.parse(s)
    isa(p, Expr) && p.head in (:using, :import) && return p
    quote $Cassette.@overdub($(RandAlwaysHalf()), $p) end
end
initrepl(parse_to_expr,
                prompt_text="RandAlwaysHalf> ",
                prompt_color = :cyan,
                start_key='£',
                mode_name="not rand mode")