Hi, Hans. Here's my (miserably failing) attempt:

\definedataset[nicedata]

\starttext

\startluacode

local name = "nicedata"

-- For exposition only

local function dofactorial(n)

local function inner(c,m)

if m<2 then return c end

return inner(c*m, m-1)

end

return inner(1,n)

end

local function factorial(n)

local stringn = tostring(n)

if job.datasets.collected[name] then

return job.datasets.collected[name].factorial[stringn]

else

local mydata = {[stringn] = tostring(dofactorial(n))}

job.datasets.setdata{

name = name,

tag = "factorial",

data = mydata

}

return mydata[stringn]

end

end

interfaces.implement{

name = "factorial",

public = true,

arguments = {"string"},

actions = {tonumber, factorial, context}

}

\stopluacode

\factorial{7}

\stoptext

What happens is that, in each run, both the first and the second conditions are met, so the compilation is twice as slow, the opposite result of what I meant to do. How do I fix that?

Jairo