[CakeML] translating mergesort

[Ramana Kumar]

Hi,

I am trying to use the CakeML translator to translate mergesort from HOL's
mergesortTheory. The main function to translate is mergesortN_def, printed
below. But the translator fails. Why? I translated sort2 and sort3 and DROP
already, so I don't think they are the problem.

val it =
   |- (∀l R. mergesortN R 0 l = []) ∧
   (∀x l R. mergesortN R 1 (x::l) = [x]) ∧
   (∀R. mergesortN R 1 [] = []) ∧
   (∀y x l R. mergesortN R 2 (x::y::l) = sort2 R x y) ∧
   (∀x R. mergesortN R 2 [x] = [x]) ∧ (∀R. mergesortN R 2 [] = []) ∧
   (∀z y x l R. mergesortN R 3 (x::y::z::l) = sort3 R x y z) ∧
   (∀y x R. mergesortN R 3 [x; y] = sort2 R x y) ∧
   (∀x R. mergesortN R 3 [x] = [x]) ∧ (∀R. mergesortN R 3 [] = []) ∧
   ∀v4 l R.
     mergesortN R v4 l =
     if v4 = 0 then []
     else if v4 = 1 then case l of [] => [] | x::l' => [x]
     else if v4 = 2 then
       case l of [] => [] | [x'] => [x'] | x'::y::l'' => sort2 R x' y
     else if v4 = 3 then
       case l of
         [] => []
       | [x''] => [x'']
       | [x''; y'] => sort2 R x'' y'
       | x''::y'::z::l''' => sort3 R x'' y' z
     else
       (let len1 = v4 DIV 2
        in
          merge R (mergesortN R (v4 DIV 2) l)
            (mergesortN R (v4 − len1) (DROP len1 l))):
   thm

Translating mergesortn
metis: r[+0+14]+0+0+0+0+0+0+0+0+0+0+0+0+0+0!
metis: r[+0+14]+0+0+0+0+0+0+0+0+0+0+0+0+0+0!
metis: r[+0+14]+0+0+0+0+0+0+0+0+0+0+0+0+0+0!
Failed translation: mergesortN
Exception- HOL_ERR {message = "no solution found", origin_function =
"FOL_FIND", origin_structure = "folTools"} raised

I to looks like there's a lot of pattern matching in the definition. What
is the status of HOL issue #285 (
https://github.com/HOL-Theorem-Prover/HOL/issues/285)? I think that might
be able to help.

Looking forward to your reply,
Ramana
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