From 67c442f41ae4af323672b359338d281f7103b361 Mon Sep 17 00:00:00 2001 From: maxonfjvipon Date: Tue, 14 May 2024 18:34:38 +0300 Subject: [PATCH 1/2] feat(#68): blog post about special attributes --- .../05/2024-05-02-rho-sigma-delta-lambda.md | 208 ++++++++++++++++++ 1 file changed, 208 insertions(+) create mode 100644 _posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md diff --git a/_posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md b/_posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md new file mode 100644 index 0000000..f1e4bba --- /dev/null +++ b/_posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md @@ -0,0 +1,208 @@ +--- +layout: post +date: 2024-05-14 +title: "Rho, Sigma, and Other Fantastic Beasts of EO" +author: maxonfjvipon + +--- + +Since the last blog post, we [released](https://github.com/objectionary/eo/releases/tag/0.38.0) a +new version of EO where we got rid of the `σ` (Sigma) attribute. So, this blog post will try to +explain all special attributes and assets such as `Δ` (Delta), `φ` (Phi), `σ` (Sigma), `λ` (Lambda), +and `ρ` (Rho) as promised in one of the previous blog posts. + + + +### Where I Was Born + +The first special attribute we're observing (and which was removed) is `σ` (Sigma). The `σ` +attribute of the object `X` was the attribute that referred to the object `Y` inside which the +scope object `X` was born (formed or created for the first time). + +The `σ` attribute in EO: +- was indicated by the `&` sign. +- was initialized right after the object is formed. +- every object except the global parent object `Φ` had it. + +For example, `int.& -> eolang`, `float.div.& -> float`. Consider the next code snippet: + +``` +[] > loop + "Hello, world" > str + + while > @ + true + [i] + stdout > @ + &.str +``` + +Here we have an endless while loop. The second argument of the object `while` is an anonymous +abstract object, let's call him `X`. The `X` object is not used in the scope of the object `loop`; +it's just created here. The object `X` will be used inside the scope of the object `while` when +dataization is started. But as you may see `X` has access to the scope of the object `loop` via +`&` and may reach the attributes of `loop` like `str`. + +And we decided that it was a bad idea to give the object such an opportunity to have access to the +place where it was born. It kind of breaks the idea of object orientation because `&` is actually +a static attribute like a static method in Java. We don't tolerate static methods and attributes, +[here's](https://www.yegor256.com/2014/05/05/oop-alternative-to-utility-classes.html) why. + +### Who Uses Me + +The second special attribute we're observing is `ρ` (Rho). The `ρ` attribute of the object `X` is +the attribute that refers to the object `Y` that uses the object `X`. In EO, the attribute `ρ` is +indicated by the `^` sign. Drawing the analogy with Java, the closest thing to `ρ` is the `this` +keyword which refers to the current object: + +``` +class Animal { + String type; + Animal(String tpe) { + this.type = tpe; + } + void voice() { + System.out.print("I'm a %s", this.type) + } +} + +Animal cat = new Animal("Cat"); +cat.voice(); // I'm a Cat + +Animal dog = new Animal("Dog"); +dog.voice(); // I'm a Dog +``` + +Here when we create two instances of `Animal` - `cat` and `dog`. The `this` keyword inside their +functions `voice` refers to different objects - `cat` and `dog` accordingly. + +The same functionality can be achieved in EO: +``` +[type] > animal + [] > voice + stdout > @ + sprintf + "I'm a %s" + ^.type + +animal "Cat" > cat +cat.voice > moew # I'm a Cat + +animal "Dog" > dog +dog.voice > woof # I'm a Dog + +``` +The main difference between `this` in Java and `ρ` in EO is the moment when these "links" actually +become referred to the objects. In Java - right after the object is created, in EO - on attribute +dispatch. Let's look a bit closer. The dynamic dispatch in EO is a mechanism of retrieving an +attribute from the object. Syntactically it's implemented via "dot-notation". + +So this is dispatch: + +``` +cat.voice +``` + +We're trying to retrieve an attribute `voice` from the concrete object `cat`. At the moment we've +found the attribute `voice` inside the object `cat` and ready to return it - the `voice` attribute +is copied and its `ρ` attribute is initialized with a link to the object `cat`. Until we touch +`cat.voice` object its `ρ` attribute refers to `Ø` (nothing). + +A few more examples: + +``` +cat.voice > voice1 # voice1.^ -> cat +cat.voice > voice2 # voice2.^ -> cat +dog.voice > voice3 # voice3.^ -> dog + +cat.voice > voice4 # voice4.& -> animal - deprecated +dog.voice > voice5 # voice5.& -> animal - deprecated +``` + +### What I Decorate + +The third special attribute we're observing is `φ` (Phi). We've already described the attribute in +one of the previous blog posts, but let's dive a bit deeper. In EO, the attribute is indicated +by `@` sign. The attribute is not mandatory and may be absent. The `φ` attribute of the object `X` +is the attribute that refers to the object `Y` which object `X` decorates. The main purpose of +decoration - reuse of the attributes. For example: + +``` +[type] > animal + [] > voice + stdout > @ + sprintf + "I'm a %s" + ^.type + +[] > cat + animal "Cat" > @ +``` + +Here we have an object `cat` which decorates an object `animal` with `type` attribute set to +`"Cat"`. That means that all the attributes which are allowed to be taken from the object `animal`, +like `voice`, are allowed to be taken from the object `cat`: + +``` +cat.voice > meow # I'm a Cat +``` + +The decoration may have several layers and all the attributes on the deepest level are available +on the top level: + +``` +[type] > animal + [] > voice + stdout > @ + sprintf + "I'm a %s" + ^.type + +[color] > cat + animal > @ + sprintf + "%s cat" + color + +[] > black-cat + cat "black" > @ +``` + +Here the object `black-cat` decorates the object `cat` and the object `cat` decorates the object +`animal`. This onion of decorators allows taking the attribute `voice` from the object `black-cat`: + +``` +black-cat.voice > meow # I'm a black cat +``` + +### What Data I Have + +The fourth special thing we're observing is `Δ` (Delta) asset. A few words about this asset: +- It's not an attribute but an asset because it refers not to the object but to the data which is + a sequence of bytes. +- There's no way to explicitly touch this asset in EO. +- Only `org.eolang.bytes` object has this asset. +- The only way to touch the data in the asset is dataization. + +### What I Can Reach from Outside + +The last special thing we're observing is `λ` (Lambda) asset. Let's look at it a bit closely: +- It's not an attribute but an asset because it refers not to the object but to some external + function which returns an object. +- Objects in EO that have the `λ` asset are called "atoms". +- There's no way to explicitly touch this asset in EO. +- Atoms can't have a `φ` attribute. +- The `λ` asset, as well as the `φ` attribute, also allows reusing the attributes: + +``` +[] > mars-termerature /float # measures the temperature on Mars and returns float + +mars-temperature.div 10 > divided +``` + +Here, as you may see, `mars-termerature` is the atom that does not have an attribute `div` and +returns `float`. However, we can still retrieve the attribute `div` from it. It will go to the +`λ` asset, execute it, do some calculations, return us some `float`, and the `div` attribute will +be taken from this `float`. + +That's all for today. We'll be right back in a week with a new fresh blog post. Stay in touch. \ No newline at end of file From dee1eb262ffb92d1a00e9e677cdd23f37dbafc3c Mon Sep 17 00:00:00 2001 From: maxonfjvipon Date: Tue, 14 May 2024 18:37:11 +0300 Subject: [PATCH 2/2] feat(#68): and --- _posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/_posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md b/_posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md index f1e4bba..6e40b42 100644 --- a/_posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md +++ b/_posts/2024/05/2024-05-02-rho-sigma-delta-lambda.md @@ -1,7 +1,7 @@ --- layout: post date: 2024-05-14 -title: "Rho, Sigma, and Other Fantastic Beasts of EO" +title: "Rho, Sigma and Other Fantastic Beasts of EO" author: maxonfjvipon ---