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wadler 2018-06-28 18:10:34 -03:00
parent 2c570407e4
commit 62b25bad76
1 changed files with 79 additions and 78 deletions
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src/plta/PandP.lagda
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@ -854,6 +854,7 @@ When our evaluator returns a term `N`, it will either give evidence that
`N` is a value or indicate that it ran out of gas. `N` is a value or indicate that it ran out of gas.
\begin{code} \begin{code}
data Finished (N : Term) : Set where data Finished (N : Term) : Set where
done : done :
Value N Value N
---------- ----------
@ -1214,7 +1215,8 @@ Show that if a term is well-typed it is not stuck,
and that any descendant of a well-typed term is also well-typed. and that any descendant of a well-typed term is also well-typed.
Combine these results to show `wttdgs`. Combine these results to show `wttdgs`.
<div class="hidden"> Answer:
If a term is well-typed, it does not get stuck. If a term is well-typed, it does not get stuck.
\begin{code} \begin{code}
unstuck : ∀ {M A} unstuck : ∀ {M A}
@ -1246,7 +1248,6 @@ wttdgs′ : ∀ {M N A}
→ ¬ (Stuck N) → ¬ (Stuck N)
wttdgs′ ⊢M M⟶*N = unstuck (preserve* ⊢M M⟶*N) wttdgs′ ⊢M M⟶*N = unstuck (preserve* ⊢M M⟶*N)
\end{code} \end{code}
</div>
#### Exercise: `progress-preservation` #### Exercise: `progress-preservation`