Re:The unreasonable effectiveness of declarative programming
by the_af on Tuesday May 19, 2020 @01:40PM
(#23237729)
> This would be an error in a language with immutable data structures
It's an error from the point of view of equational thinking; (im)mutabilty is not involved.
The name `x` cannot be 1 and 3 simultaneously. It's either 1 or 3. So in the allegedly declarative program, the programmer first claimed name `x` is bound to the value 1, but later claimed it's 3. That's the error.
This has nothing to do with mutating data structures. Like the sibling comment notes, there is not "first-this-then-that" order of evaluation, so you cannot read this as "first `x` means 1, but later it means 3", because there are no notions of "first" and "later".
It's an error from the point of view of equational thinking; (im)mutabilty is not involved.
The name `x` cannot be 1 and 3 simultaneously. It's either 1 or 3. So in the allegedly declarative program, the programmer first claimed name `x` is bound to the value 1, but later claimed it's 3. That's the error.
This has nothing to do with mutating data structures. Like the sibling comment notes, there is not "first-this-then-that" order of evaluation, so you cannot read this as "first `x` means 1, but later it means 3", because there are no notions of "first" and "later".