> - Adjective strict can be applied both to a global evaluation method and a specific function: if applied to an eval method then it's a synonym of "strict"

I of course meant a synonym of "eager". Sorry.

I admit this definition might be a little liberal, but it helps understand.


2011/12/28 Yves Parès <limestrael@gmail.com>
When I explain to people what strict/lazy/eager mean, I often say something like :

- Adjectives eager and lazy apply only to a global evaluation method: eager is C evaluation style and lazy is that of Haskell.
- Adjective strict can be applied both to a global evaluation method and a specific function: if applied to an eval method then it's a synonym of "strict", and if applied to a function f it means 'f ⊥ = ⊥' (which I detail a little more), which is true for strict State monad for istance (>>= would not allow its left argument to return ⊥).

Thus explaining why datatypes such as State or Bytestring exist in strict and lazy flavours.


2011/12/28 Albert Y. C. Lai <trebla@vex.net>

There are two flavours of MonadState, Control.Monad.State.Lazy and Control.Monad.State.Strict. There are two flavours of ByteString, Data.ByteString.Lazy and Data.Bytestring (whose doc says "strict"). There are two flavours of I/O libraries, lazy and strict. There are advices of the form: "the program uses too much memory because it is too lazy; try making this part more strict". Eventually, someone will ask what are "lazy" and "strict". Perhaps you answer this (but there are other answers, we'll see):

"lazy refers to such-and-such evaluation order. strict refers to f ⊥ = ⊥, but it doesn't specify evaluation order."

That doesn't answer the question. That begs the question: Why do libraries seem to make them a dichotomy, when they don't even talk about the same level? And the make-it-more-strict advice now becomes: "the program uses too much memory because of the default, known evaluation order; try making this part use an unknown evaluation order", and this unknown is supposed to use less memory because...?

I answer memory questions like this: the program uses too much memory because it is too lazy---or nevermind "lazy", here is the current evaluation order of the specific compiler, this is why it uses much memory; now change this part to the other order, it uses less memory. I wouldn't bring in the denotational level; there is no need.

(Sure, I use seq to change evaluation order, which may be overriden by optimizations in rare cases. So change my answer to: now add seq here, which normally uses the other order, but optimizations may override it in rare cases, so don't forget to test. Or use pseq.)

I said "people, make up your mind". I do not mean a whole group of people for the rest of their lives make up the same mind and choose the same one semantics. I mean this: Each individual, in each context, for each problem, just how many levels of semantics do you need to solve it? (Sure sure, I know contexts that need 4. What about daily programming problems: time, memory, I/O order?)

MigMit questioned me on the importance of using the words properly. Actually, I am fine with using the words improperly, too: "the program uses too much memory because it is too lazy, lazy refers to such-and-such evaluation order; try making this part more strict, strict refers to so-and-so evaluation order".



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