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Bug in size preservation #2

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Bug in size preservation #2

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38 changes: 38 additions & 0 deletions test/Bugs/TBTShiftShouldNotBeSizePreserving.agda
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Original file line number Diff line number Diff line change
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{-# OPTIONS --type-based-termination #-}
-- {-# OPTIONS -v term.tbt:40 #-}

module _ where

data Nat : Set where
zero : Nat
suc : Nat → Nat

data Maybe (A : Set) : Set where
nothing : Maybe A
just : A → Maybe A

shift_case : Maybe Nat → Maybe Nat
shift_case nothing = nothing
shift_case (just zero) = nothing
shift_case (just (suc x)) = just x

-- Should not be size preserving
shift : (Nat → Maybe Nat) → (Nat → Maybe Nat)
shift f n = shift_case (f (suc n))

inc : Nat → Maybe Nat
inc n = just (suc n)

-- This is luckily not recognized as size preserving
shift_inc : Nat → Maybe Nat
shift_inc n = shift inc n

-- Should be rejected
test : Maybe Nat → Maybe Nat
test nothing = nothing
test (just zero) = nothing
test (just (suc n)) = test (shift inc n)

-- Don't normalize this!
diverge : Maybe Nat
diverge = test (just (suc zero))
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