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Lean: Matches on heterogeneous bitvector lengths #1070

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javra opened this issue Feb 25, 2025 · 0 comments · May be fixed by #1071
Open

Lean: Matches on heterogeneous bitvector lengths #1070

javra opened this issue Feb 25, 2025 · 0 comments · May be fixed by #1071
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@javra
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Lean Issues with Sail to Lean translation

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javra commented Feb 25, 2025

Problem can be exposed via

function const16() -> (bitvector(16), bool) = {
  (0xFFFF, true)
}

function const32() -> (bitvector(32), bool) = {
  (0xEEEE_EEEE, false)
}

val match_width : forall 'n, 'n >= 0. bitvector('n) -> bitvector(2 * 'n)
function match_width x = {
  let (foo, _) : (bitvector('n), bool) = match 'n {
    16 => const16(),
    32 => const32(),
    n => (sail_zeros(n), false)
  } in
  bitvector_concat(foo, foo)
}

which gets translated to

...

/-- Type quantifiers: k_n : Nat, k_n ≥ 0 -/
def match_width (x : (BitVec k_n)) : (BitVec (2 * k_n)) :=
  let (foo, _) :=
    match (Sail.BitVec.length x) with
    | 16 => (const16 ())
    | 32 => (const32 ())
    | n => ((BitVec.zero n), false)
  (foo ++ foo)

The solution is to

  1. keep the type ascription
  2. add instances to carry our new coercions over products
@javra javra added the Lean Issues with Sail to Lean translation label Feb 25, 2025
@javra javra self-assigned this Feb 25, 2025
@javra javra linked a pull request Feb 25, 2025 that will close this issue
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Lean: Allow for match statments of heterogeneous bitvector length javra/sail
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