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Explicit α-conversion #3

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ayberkt opened this issue Feb 5, 2016 · 1 comment
Closed

Explicit α-conversion #3

ayberkt opened this issue Feb 5, 2016 · 1 comment
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ayberkt commented Feb 5, 2016

α-captures are correctly handled in terms of semantics, but the displayed expression doesn't display the α-conversion.

4) z y z
3) (λx. x y) z z
2) (λy. (λx. x y) y z) z
1) (λx. λy. x y z) (λx. x y) z

At step 2 we should have something like (λn. (λx. x y) n z) z so that the conversion is made explicit.

A minor problem, but wanted to make note of it in case there are people confused. It should be trivial to fix.
@cdparks cdparks self-assigned this Feb 7, 2016
@cdparks cdparks mentioned this issue Feb 7, 2016
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@cdparks cdparks closed this as completed in #4 Feb 7, 2016
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cdparks commented Feb 7, 2016

Thanks for the heads-up!

cdparks added a commit that referenced this issue May 22, 2021
@cdparks
Don't create new globals in instantiateAt
908d8d9 
When a lambda's body was just a free variable, we were creating a new
global that pointed at the real global. For example, suppose "false"
is at address #1, and we're reducing the input at address #3:

  #1: Global "false" #2
  #2: Closure (λt. λf. f)
  #3: Apply #4 #5 <---------[input]--------> (λa. false) (λb. b)
  #4: Closure (λa. false)
  #5: Closure (λb. b)

We would reduce the input as follows:

  1. (λa. false) (λb. b)
  2. false
  3. false
  4. λt. λf. f

This is because we were instantating the body of the lambda by creating
a new Global:

  #1: Global "false" #2
  #2: Closure (λt. λf. f)
  #3: Global "false" #1

Instead of a new pointer:

  #1: Global "false" #2
  #2: Closure (λt. λf. f)
  #3: Pointer #1

And then we would have to unwind and fetch the global twice. The fix is
to use a Pointer instead (which we correctly keep unwinding through).
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