7 ms·

Why I love Smalltalk

86 points by mordaroso 15y ago

JoachimSchipper 15y ago
Copy of the text, since it's hard to reach the site itself [any layout errors should be assumed to be mine]: This post was extracted from a small talk I gave at Simplificator, where I work, titled “Why I love Smalltalk and Lisp”. There should be another post, “Why I love Lisp” following this one. After I learned my basic coding skill in more or less traditional languages, like C, C++, Python, there were four languages that really tought me something new. Those languages changed my way of thinking and even if I never use them, they were worth learning. They are: * Smalltalk * Lisp * Erlang * Haskell You can probably add Prolog to that list, but I never learned Prolog. This post is about Smalltalk. My goal is not to teach Smalltalk but to show things that you can do with Smalltalk that you can’t do with any other language (disclaimer: surely other languages can do it, and we’ll call them Smalltalk dialects). Nevertheless I need to show you some basics of the language to be able to show you the good stuff, so here we go, a first program: 1 + 1 That of course, evaluates to 2. If we want to store it in a variable: m := 1 + 1 Statements are finished by a period, like this: m := 1. m := m + 1 In Squeak, a Smalltalk implementation, there’s an object called Transcript and you can send messages to it to be displayed on the screen. It’s more or less like a log window. It works like this: Transcript show: 'Hello world' and it looks like this: [Squeak transcript showing the result of Transcript show: 'Hello World'] The syntax is quite unique to Smalltalk. The message, otherwise known as “method call” in other languages, is called show: (including the colon) and it takes an argument. We can run it 10 times in a row with the following snippet: 10 timesRepeat: [ Transcript show: 'Hello world' ] There you can start to see how Smalltalk is special. I’m sending the message timesRepeat: to the object 10, an Integer. Doing something N times repeatedly is handled by the Integer class, which if you think about it, makes sense. The second interesting part, is the block. The part inside squared brackets. You might thing that’s the equivalent of other language’s block syntax, like in this Java example: for(int i=1; i<11; i++) { System.out.println("Hello world"); } but Smalltalk version’s is a bit more powerful. It’s a real closure. Look at this: t := [ Transcript show: 'Hello world' ] Now I have a variable named t, of type BlockClosure, and I can do anything I want with that variable. If I send it the class message it’ll return it’s class: t class and if I sed it the value message, it’ll execute and leave a “Hello World” in the transcript: t value Let’s see some more code. A message without any arguments: 10 printString a message with one argument: 10 printStringBase: 2 and a message with two arguments: 10 printStringBase: 2 nDigits: 10 Isn’t it cute? That method is called printStringBase:nDigits:. I never seen that syntax anywhere else; well, except in Objective-C, which copied it from Smalltalk. Enough toying around, let’s start building serious stuff. Let’s create a class: Object subclass: #MyClass instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' Notice that a class is created by sending a message to another class telling it to subclass itself with the name and a few other arguments. It’s a message, a method call like any other. Object is a class, classes are objects. The object model of Smalltalk is a beauty but that’s a subject for another post. Now that we have a class, let’s create a method called greet: in that class. greet: name "Greets the user named name" | message | message := 'Hello ', name. Transcript show: message. In that method definition first we have a comment for the method, then the list of local variables within pipes (“|”), and then the implementation, which sets the variable message to contain “Hello ” and the comma concatenates name to it. Then we just send it to the transcript. It looks like this: MyClass greet method Ok, let’s use it: m := MyClass new. m greet: 'Pupeno' To create an object of class MyClass, we send the new message to that class. There’s no new keyword like in Java. new is just a method. You can read it’s code, override it, etc. Don’t mess with it unless you really know what you are doing. Actually, if you think about it, we haven’t seen a single keyword. Look all the code we wrote without having to memorize any keywords! What’s even more important is that by now you essentially now Smalltalk. That’s all there is, but like LEGO bricks, this simple and small building blocks allow you to build whatever you want. Yes, that’s it, that’s all there is to it. We already saw that Smalltalk doesn’t need loops, it has integers and that class implements the timesRepeat: message which allows you to do something N times. There are many other looping methods here and there. What about the if keyword you ask? Surely Smalltalk has an if? Well, no, it doesn’t. What you can recognize as an if is actually implemented in Smalltalk using the same mechanism of classes and message passing you saw already. Just for fun let’s re-implement it. We starte by creating the class PBoolean and then two classes inheriting from it, PTrue and PFalse. Object subclass: #PBoolean instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' PBoolean subclass: #PTrue instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' PBoolean subclass: #PTrue instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' For the class we created before, MyClass, we define a equals: method that will return either true or false, or rather, PTrue or PFalse. equals: other ^ PTrue new The little hat, ^, means return. For now, just a hardcoded true. Now we can do this in the workspace: m1 := MyClass new. m2 := MyClass new. m1 equals: m2 and get true, that is PTrue, as a result. We are getting close but no if yet. How should if look like? It’ll look like something like this: m1 := MyClass new. m2 := MyClass new. (m1 equals: m2) ifTrue: [ Transcript show: 'They are equal'; cr ] else: [ Transcript show: 'They are false'; cr ] and you can start to imagine how to implement it. In PTrue we add the method: ifTrue: do else: notdo ^ do value That method basically takes two parameters, evaluates the first one and ignores the second one. For PFalse we create the oposite: ifTrue: notdo else: do ^ do value and that’s it. A working if! If you ask me, I think this is truly amazing. And if you check Squeak itself, you’ll find the if is actually implemented this way: True's ifTrue:ifFalse: If your programming language allows you to create something as basic as the if conditional, then it allows you to create anything you want.
- RodgerTheGreat 15y ago
  Forth can be used to create 'if' statements from scratch, too. Many Forth implementations start up by loading a set of definitions for things like comments, conditionals and flow control. : IF COMPILE 0BRANCH HERE 0 , ; IMMEDIATE : ELSE COMPILE BRANCH HERE SWAP 0 , HERE SWAP ! ; IMMEDIATE : THEN HERE SWAP ! ; IMMEDIATE
- mbrzuzy 15y ago
  Appreciated :) I'm unable to access the site at all right now. HN traffic might have brought it down.
  - pupeno 15y ago
    Indeed it has! My server is smoking :P
- pupeno 15y ago
  Yeah, you guys killed my server... it's appreciated anyway.
redxaxder 15y ago
equals: other ^ PTrue new The implementation of ifTrue isn't done. The branching was just deferred to the equals function, which has to somehow choose between PTrue and PFalse. Will it take advantage of the ifTrue function you're building? Will it resort to some nasty arithmetic? Will it call some baked-in feature of smalltalk? Without an answer here, the "implementation" of if is just an illusion.
- gjm11 15y ago
  I don't think that's fair. Being able to implement if doesn't mean that the entire remainder of the system is built without any conditional instructions anywhere in its implementation. (The point, after all, isn't some sort of mystical purity; it's that if you can implement if then you can probably also implement whatever other control structures you happen to fancy. Which you can.)
  - chc 15y ago
    Actually, that really is how Smalltalk does if.
    - pupeno 15y ago
      In the blog post I include a screenshot of it... but my server is dying at the moment.
  - JoelMcCracken 15y ago
    The problem is that reading this seems very bait-and-switch-y. Basically, author is doing: (define (my-if cond t f) (if cond (t) (f))) (my-if #t (lambda () ....) (lambda () ....)) The trickyness about if lies in the order of argument evaluation. If you ignore that, then it is relatively easy to implement if in any reasonable language. Even C (I had to leave out the function pointer types, as I haven't worked with c in a few years, and forget the syntax): void my_if(bool cond, t, f) { if(cond) { t(); } else { f(); } } void if_true() { ... } void if_false() { } my_if(true, if_true, if_false); Point being, I think redxaxder may have been coming from a scheme background, realizing that if needs to be a builtin. It would indeed be fancy to be able to implement an if that doesn't rely upon other logical branching, though!
draegtun 15y ago
The syntax is quite unique to Smalltalk. The message, otherwise known as “method call” in other languages, is called show: (including the colon) and it takes an argument. self also uses this method call syntax. However this syntax can get quite confusing, see this example from http://en.wikipedia.org/wiki/Self_(programming_language) http://en.wikipedia.org/wiki/Self_(programming_language) valid: base bottom between: ligature bottom + height and: base top / scale factor. Smalltalk version provided gets even more verbose: valid := self base bottom between: self ligature bottom + self height and: self base top / self scale factor. Personally I prefer Io message syntax because it has far less ambiguity. See Why not use an infix message syntax like Smalltalk? in the FAQ - http://iolanguage.com/about/faq/ http://iolanguage.com/about/faq/
- eterps 15y ago
  So, what would the syntax be in Io? Like this? valid := base bottom between(ligature bottom + height, base top / scale factor)
  - draegtun 15y ago
    Yes, unless I've totally misunderstood that Self/Smalltalk code! Also instead of between method with two args you could also create an and message/method: valid := base bottom between(ligature bottom + height) and(base top / scale factor)
- pupeno 15y ago
  As far as I know both Self and Slate are very strongly inspired by Smalltalk.
- treetrouble 15y ago
  Thank you, I wasn't familiar with Io before
  - draegtun 15y ago
    Your very welcome. Like Smalltalk, its a beautifully designed language. Some quick examples: 10 repeat("Hello world" println) (y < 10) ifTrue(x := y) ifFalse(x := 2) if (y < 10, x := y, x := 2) More example Io code can be found here: http://iolanguage.com/about/samplecode/ http://iolanguage.com/about/samplecode/
xradionut 15y ago
I like Smalltalk, but like Forth and Lisp it's just not practical in most of my computing tasks, career or hobby-wise. It's a shame that Smalltalk didn't evolve enough to challenge Java in the '90s. But my buds that knew it well and also had some C chops are in demand as Objective C coders.
- pupeno 15y ago
  I agree with you about Smalltalk and most Lisps not being practical. I think Clojure has the power to change that though.
- Xurinos 15y ago
  The word you were looking for was "popular", not "practical". Our industry is largely internally rife with fads, marketing, and anecdotal discussion, rather than objective analysis and scientific measurement. And then, this statement is just blaming the tools rather than the developers. "C chops" means less than "has good logical thinking skills and exposure to many programming approaches/patterns".
  - pupeno 15y ago
    I disagree. Every time I tried to put together an app with any of Common Lisp, Scheme or Smalltalk I found myself fighting idiosyncrasies unrelated to my app. Obviously it can be done, but the advantage of using those languages start to diminish. It's not about popularity, it's about practicality. I found making Java web applications unpractical in a similar way although I haven't tried enough.
    - Xurinos 15y ago
      This is an example of an anecdotal piece of evidence, and without a close examination of the "idiosyncrasies" and your definition of "practical", it is difficult to have a discussion. I recognize, though, that people have different opinions on what language is most familiar/useful to them, and at the end of the day, people get work done and make money, whatever they use.
hboon 15y ago
It covers some of the minimal syntax of Smalltalk but didn't touch on Smalltalk images, which is a major signature of Smalltalk. A Smalltalk image contains every Smalltalk object. This includes classes (which are Smalltalk objects), instances of the classes, source code, the current running state, everything. You work within the image and interact with it. Think of the image as a copy of your IDE, along with the compiler, your current project's source code, the compiled classes, methods, everything. You can save your image (state) at any time, not unlike the sleep feature of Windows and Mac. It's a live environment. During a programming session, you edit and save the code of class (it's automatically compiled) and every instance of that class is updated. This sounds like what you commonly have in many dynamic languages, but Smalltalk takes it to an extreme. You can re-configure your "IDE" as you go along since they are running in the same image, all the classes and objects are accessible. Or you can set breakpoints and step through code, changing code on the fly and resuming, all without stopping the "program" and starting again. Not unlike a graphical REPL. Does anyone know if there's a similar tool utilizing the same concept other than Self?
- pupeno 15y ago
  I consider the image an implementation detail of Squeak or the original Smalltalk-implementation. You can implement Smalltalk the language without the image: http://smalltalk.gnu.org/ http://smalltalk.gnu.org/

86 points by mordaroso 15y ago

Copy of the text, since it's hard to reach the site itself [any layout errors should be assumed to be mine]: This post was extracted from a small talk I gave at Simplificator, where I work, titled “Why I love Smalltalk and Lisp”. There should be another post, “Why I love Lisp” following this one. After I learned my basic coding skill in more or less traditional languages, like C, C++, Python, there were four languages that really tought me something new. Those languages changed my way of thinking and even if I never use them, they were worth learning. They are: * Smalltalk * Lisp * Erlang * Haskell You can probably add Prolog to that list, but I never learned Prolog. This post is about Smalltalk. My goal is not to teach Smalltalk but to show things that you can do with Smalltalk that you can’t do with any other language (disclaimer: surely other languages can do it, and we’ll call them Smalltalk dialects). Nevertheless I need to show you some basics of the language to be able to show you the good stuff, so here we go, a first program: 1 + 1 That of course, evaluates to 2. If we want to store it in a variable: m := 1 + 1 Statements are finished by a period, like this: m := 1. m := m + 1 In Squeak, a Smalltalk implementation, there’s an object called Transcript and you can send messages to it to be displayed on the screen. It’s more or less like a log window. It works like this: Transcript show: 'Hello world' and it looks like this: [Squeak transcript showing the result of Transcript show: 'Hello World'] The syntax is quite unique to Smalltalk. The message, otherwise known as “method call” in other languages, is called show: (including the colon) and it takes an argument. We can run it 10 times in a row with the following snippet: 10 timesRepeat: [ Transcript show: 'Hello world' ] There you can start to see how Smalltalk is special. I’m sending the message timesRepeat: to the object 10, an Integer. Doing something N times repeatedly is handled by the Integer class, which if you think about it, makes sense. The second interesting part, is the block. The part inside squared brackets. You might thing that’s the equivalent of other language’s block syntax, like in this Java example: for(int i=1; i<11; i++) { System.out.println("Hello world"); } but Smalltalk version’s is a bit more powerful. It’s a real closure. Look at this: t := [ Transcript show: 'Hello world' ] Now I have a variable named t, of type BlockClosure, and I can do anything I want with that variable. If I send it the class message it’ll return it’s class: t class and if I sed it the value message, it’ll execute and leave a “Hello World” in the transcript: t value Let’s see some more code. A message without any arguments: 10 printString a message with one argument: 10 printStringBase: 2 and a message with two arguments: 10 printStringBase: 2 nDigits: 10 Isn’t it cute? That method is called printStringBase:nDigits:. I never seen that syntax anywhere else; well, except in Objective-C, which copied it from Smalltalk. Enough toying around, let’s start building serious stuff. Let’s create a class: Object subclass: #MyClass instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' Notice that a class is created by sending a message to another class telling it to subclass itself with the name and a few other arguments. It’s a message, a method call like any other. Object is a class, classes are objects. The object model of Smalltalk is a beauty but that’s a subject for another post. Now that we have a class, let’s create a method called greet: in that class. greet: name "Greets the user named name" | message | message := 'Hello ', name. Transcript show: message. In that method definition first we have a comment for the method, then the list of local variables within pipes (“|”), and then the implementation, which sets the variable message to contain “Hello ” and the comma concatenates name to it. Then we just send it to the transcript. It looks like this: MyClass greet method Ok, let’s use it: m := MyClass new. m greet: 'Pupeno' To create an object of class MyClass, we send the new message to that class. There’s no new keyword like in Java. new is just a method. You can read it’s code, override it, etc. Don’t mess with it unless you really know what you are doing. Actually, if you think about it, we haven’t seen a single keyword. Look all the code we wrote without having to memorize any keywords! What’s even more important is that by now you essentially now Smalltalk. That’s all there is, but like LEGO bricks, this simple and small building blocks allow you to build whatever you want. Yes, that’s it, that’s all there is to it. We already saw that Smalltalk doesn’t need loops, it has integers and that class implements the timesRepeat: message which allows you to do something N times. There are many other looping methods here and there. What about the if keyword you ask? Surely Smalltalk has an if? Well, no, it doesn’t. What you can recognize as an if is actually implemented in Smalltalk using the same mechanism of classes and message passing you saw already. Just for fun let’s re-implement it. We starte by creating the class PBoolean and then two classes inheriting from it, PTrue and PFalse. Object subclass: #PBoolean instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' PBoolean subclass: #PTrue instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' PBoolean subclass: #PTrue instanceVariableNames: '' classVariableNames: '' poolDictionaries: '' category: 'Pupeno' For the class we created before, MyClass, we define a equals: method that will return either true or false, or rather, PTrue or PFalse. equals: other ^ PTrue new The little hat, ^, means return. For now, just a hardcoded true. Now we can do this in the workspace: m1 := MyClass new. m2 := MyClass new. m1 equals: m2 and get true, that is PTrue, as a result. We are getting close but no if yet. How should if look like? It’ll look like something like this: m1 := MyClass new. m2 := MyClass new. (m1 equals: m2) ifTrue: [ Transcript show: 'They are equal'; cr ] else: [ Transcript show: 'They are false'; cr ] and you can start to imagine how to implement it. In PTrue we add the method: ifTrue: do else: notdo ^ do value That method basically takes two parameters, evaluates the first one and ignores the second one. For PFalse we create the oposite: ifTrue: notdo else: do ^ do value and that’s it. A working if! If you ask me, I think this is truly amazing. And if you check Squeak itself, you’ll find the if is actually implemented this way: True's ifTrue:ifFalse: If your programming language allows you to create something as basic as the if conditional, then it allows you to create anything you want.

RodgerTheGreat 15y ago
Forth can be used to create 'if' statements from scratch, too. Many Forth implementations start up by loading a set of definitions for things like comments, conditionals and flow control. : IF COMPILE 0BRANCH HERE 0 , ; IMMEDIATE : ELSE COMPILE BRANCH HERE SWAP 0 , HERE SWAP ! ; IMMEDIATE : THEN HERE SWAP ! ; IMMEDIATE
mbrzuzy 15y ago
Appreciated :) I'm unable to access the site at all right now. HN traffic might have brought it down.
- pupeno 15y ago
  Indeed it has! My server is smoking :P
pupeno 15y ago
Yeah, you guys killed my server... it's appreciated anyway.

redxaxder 15y ago

equals: other ^ PTrue new The implementation of ifTrue isn't done. The branching was just deferred to the equals function, which has to somehow choose between PTrue and PFalse. Will it take advantage of the ifTrue function you're building? Will it resort to some nasty arithmetic? Will it call some baked-in feature of smalltalk? Without an answer here, the "implementation" of if is just an illusion.

gjm11 15y ago
I don't think that's fair. Being able to implement if doesn't mean that the entire remainder of the system is built without any conditional instructions anywhere in its implementation. (The point, after all, isn't some sort of mystical purity; it's that if you can implement if then you can probably also implement whatever other control structures you happen to fancy. Which you can.)
- chc 15y ago
  Actually, that really is how Smalltalk does if.
  - pupeno 15y ago
    In the blog post I include a screenshot of it... but my server is dying at the moment.
- JoelMcCracken 15y ago
  The problem is that reading this seems very bait-and-switch-y. Basically, author is doing: (define (my-if cond t f) (if cond (t) (f))) (my-if #t (lambda () ....) (lambda () ....)) The trickyness about if lies in the order of argument evaluation. If you ignore that, then it is relatively easy to implement if in any reasonable language. Even C (I had to leave out the function pointer types, as I haven't worked with c in a few years, and forget the syntax): void my_if(bool cond, t, f) { if(cond) { t(); } else { f(); } } void if_true() { ... } void if_false() { } my_if(true, if_true, if_false); Point being, I think redxaxder may have been coming from a scheme background, realizing that if needs to be a builtin. It would indeed be fancy to be able to implement an if that doesn't rely upon other logical branching, though!

draegtun 15y ago

The syntax is quite unique to Smalltalk. The message, otherwise known as “method call” in other languages, is called show: (including the colon) and it takes an argument. self also uses this method call syntax. However this syntax can get quite confusing, see this example from http://en.wikipedia.org/wiki/Self_(programming_language) http://en.wikipedia.org/wiki/Self_(programming_language) valid: base bottom between: ligature bottom + height and: base top / scale factor. Smalltalk version provided gets even more verbose: valid := self base bottom between: self ligature bottom + self height and: self base top / self scale factor. Personally I prefer Io message syntax because it has far less ambiguity. See Why not use an infix message syntax like Smalltalk? in the FAQ - http://iolanguage.com/about/faq/ http://iolanguage.com/about/faq/

eterps 15y ago
So, what would the syntax be in Io? Like this? valid := base bottom between(ligature bottom + height, base top / scale factor)
- draegtun 15y ago
  Yes, unless I've totally misunderstood that Self/Smalltalk code! Also instead of between method with two args you could also create an and message/method: valid := base bottom between(ligature bottom + height) and(base top / scale factor)
pupeno 15y ago
As far as I know both Self and Slate are very strongly inspired by Smalltalk.
treetrouble 15y ago
Thank you, I wasn't familiar with Io before
- draegtun 15y ago
  Your very welcome. Like Smalltalk, its a beautifully designed language. Some quick examples: 10 repeat("Hello world" println) (y < 10) ifTrue(x := y) ifFalse(x := 2) if (y < 10, x := y, x := 2) More example Io code can be found here: http://iolanguage.com/about/samplecode/ http://iolanguage.com/about/samplecode/

xradionut 15y ago

I like Smalltalk, but like Forth and Lisp it's just not practical in most of my computing tasks, career or hobby-wise. It's a shame that Smalltalk didn't evolve enough to challenge Java in the '90s. But my buds that knew it well and also had some C chops are in demand as Objective C coders.

pupeno 15y ago
I agree with you about Smalltalk and most Lisps not being practical. I think Clojure has the power to change that though.
Xurinos 15y ago
The word you were looking for was "popular", not "practical". Our industry is largely internally rife with fads, marketing, and anecdotal discussion, rather than objective analysis and scientific measurement. And then, this statement is just blaming the tools rather than the developers. "C chops" means less than "has good logical thinking skills and exposure to many programming approaches/patterns".
- pupeno 15y ago
  I disagree. Every time I tried to put together an app with any of Common Lisp, Scheme or Smalltalk I found myself fighting idiosyncrasies unrelated to my app. Obviously it can be done, but the advantage of using those languages start to diminish. It's not about popularity, it's about practicality. I found making Java web applications unpractical in a similar way although I haven't tried enough.
  - Xurinos 15y ago
    This is an example of an anecdotal piece of evidence, and without a close examination of the "idiosyncrasies" and your definition of "practical", it is difficult to have a discussion. I recognize, though, that people have different opinions on what language is most familiar/useful to them, and at the end of the day, people get work done and make money, whatever they use.

hboon 15y ago

It covers some of the minimal syntax of Smalltalk but didn't touch on Smalltalk images, which is a major signature of Smalltalk. A Smalltalk image contains every Smalltalk object. This includes classes (which are Smalltalk objects), instances of the classes, source code, the current running state, everything. You work within the image and interact with it. Think of the image as a copy of your IDE, along with the compiler, your current project's source code, the compiled classes, methods, everything. You can save your image (state) at any time, not unlike the sleep feature of Windows and Mac. It's a live environment. During a programming session, you edit and save the code of class (it's automatically compiled) and every instance of that class is updated. This sounds like what you commonly have in many dynamic languages, but Smalltalk takes it to an extreme. You can re-configure your "IDE" as you go along since they are running in the same image, all the classes and objects are accessible. Or you can set breakpoints and step through code, changing code on the fly and resuming, all without stopping the "program" and starting again. Not unlike a graphical REPL. Does anyone know if there's a similar tool utilizing the same concept other than Self?

pupeno 15y ago
I consider the image an implementation detail of Squeak or the original Smalltalk-implementation. You can implement Smalltalk the language without the image: http://smalltalk.gnu.org/ http://smalltalk.gnu.org/