I told my 2nd year CS students to create a programming language [RESULTS] | Hacker News Reader

I told my 2nd year CS students to create a programming language [RESULTS]

dovyski.com

17 pointsdovyski13 comments

This is a very cool experiment, this should be standard practice in teaching CS. I'm a little surprised at the limitations of their interpreters, given the fact that they are 2nd year already - but then again, they were given the task do develop a language for a very specific test case.

The absence of support for nested loop/if constructs probably means they didn't write parsers that generate trees, but rather chose to execute scripts line-by-line, right?

I'd like to ask you fellow hackers: if you created a toy programming language today, what features would it have?

Thanks! I was a little surprised too, but I think they focused too much on the test case, not the language itself.

About your (first) question, yes, they all execute scripts line-by-line.

Ok, I'll be the slow witted one in the room - When creating your own language, what did you write it in? If you're using Java or C, are you still using it's compiler but coming up with your own syntax? I'm a little confused how it worked.

Good question. You can write a language in any other language. Say you create a language called LASERD and chose to write it in C:

You write a program in C that is able to transform LASERD source files in to a form that it can interpret and then execute.

One way to do this is to create a simple virtual machine as part of your C program that is sort of like a virtual CPU (with registers, pretend memory and simple opcodes like ADD, SUBtract, MOVe etc.

The C program takes the LASERD source file interprets the syntax and generates code that can 'run' on the virtual CPU.

This is basically how Lua, Python, Ruby, Java etc work.

Does that make sense?

It makes sense to me. Even though this is the "right" way of creating an "interpreted" language, the assignment I asked my students was way more simple: they had to interpret the source code and react to it immediately. There was no intermediate instructions (such as Java byte-code).

Awesome, thanks for the explanation :)

There exists tons of "toy" language implementation available online. I wonder why no students came up with a forth or lisp like solution that would have been able to handle nested loops, ifs, etc...

When I was in my 2nd year as a CS student, one of the assignment was to reimplement the Unix's M4 preprocessor (a superset of C's preprocessor), based on its manual... It includes an expression evaluator, we were told that tools like lex and yacc would help...

Well... that was 25 years ago.

I guess I forgot to mention, but one pair of students came up with a Forth like solution. Their interpreter was even able to parse the source code backwards.

"I think it happened because they wrote just C code until now (they will meet PHP next semester)."

This surprises me. Of the higher-level languages you (or your school) could choose, why PHP? I understand for beginners, but why for students coming from a C background?

When I arrived, PHP was already chosen. I think PHP was chosen because it is very similar to C and it lowers the learning curve for the students.

I know PHP sucks sometimes, but it's still a cool language to play with.

PHP hate is often a knee-jerk reaction here on HN. It's a language that has both some very cool features and some legacy baggage it carries around - and it's absolutely possible to use it for good (and to use it well). I think PHP's image problem comes from the perception that there is some very low-quality code out there, but it's definitely mainly an in-group coolness issue.

It's one of those things that (negatively) surprised me about Hacker News, actually. People go around and unproductively bash each other's programming languages when they could use their energy to elaborate on the stuff they actually like. The group consensus seems to be that Lisp is the best thing a language can hope to be; and since very few people actually develop in Lisp-likes, they fall over each other to claim the next-best place in the All-Time Universal Programming Language Hierarchy(tm).

I believe the origin of this behavior might be a somewhat mistaken PG essay[1] implying that all non-Lisp languages are "Blub", which is a synonym for "sucky, powerless, inferior language".

[1] http://www.paulgraham.com/avg.html

I totally agree with you! I think every language has its own benefits/problems, the programmer is the one that makes the difference.

I'm sure I can find crappy Ruby/Lisp/whatever code and excellent PHP code out there. If you are a bad programmer, you write bad code. Of couse there are languages that try to prevent that forcing you to follow certain patterns, but it will not stop bad programmers.

yea I thought the same.. why PHP!! there are a lot of other languages to learn, Java, ruby, python etc etc

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