Thanks for sharing, this is really helping me to understand in a little more detail how compilers work. And the doge example gave me a good chuckle.
Learn C and build your own Lisp
51–60 of 150 posts
Re: Learn C and build your own Lisp
#52I am new to programming. What is it so special about Lisp that I keep hearing about it in Hacker's News (often in Machine Learning and from old programmers)?
Re: Learn C and build your own Lisp
#53Of course C is not the only option, and perhaps not an option at all for newbies.
JavaCC can be a good medium to build your own language too. They recently added the ability to generate C/C++ code (https://java.net/projects/javacc)
Is there any tree building capabilities using C?
Re: Learn C and build your own Lisp
#54How good is this book for a complete beginner? I am starting to learn C in my free time and I have no objective way to judge this book.
Like others, I would suggest K&R. Perhaps after that, Lourdon's "Mastering algorithms with C". I've found that structuring any program around well understood datastructures and keeping it KISS after that takes you a very long way. Also applies to C. Like others have commented, stylistically the code in the linked book is perhaps not the best place to learn the best conventions for C. But! Writing an interpreter gives…
I disagree with recommendation of Lua. Lua is a production-grade interpreter, and a production-grade interpreter is usually not a good educational material for those "interested in interpreters".
In particular, Lua uses no intermediate representation (there is no Lua AST!), which makes its compiler portion a quite confusing read. Its interpreter portion is no less confusing, being a register VM with a register window scheme and a non-recursive eval using goto and a separate call stack. Do not be fooled by "not too large" aspect. Lua is worth studying, but it is definitely not a beginner material.
Re: Learn C and build your own Lisp
#55Does it use a generator to generate lexer and parser or author is suggesting to write them manually?
Author here. A parser combinator library is used to do the parsing.
Too bad, always everyone who teaches how to write a programming language uses generators but actual production programming languages never use them. Except of a few langugages.
I wonder why...
Re: Learn C and build your own Lisp
#56Please don't. Rather pick something like "Compiler Construction" from Niklaus Wirth and learn how to write compilers using memory safe system programming languages. http://www.ethoberon.ethz.ch/WirthPubl/CBEAll.pdf
Perhaps you could suggest your favorite method as an alternative? If I get to know you, i might change my opinion, but from the little I know I would suggest you avoid a career in teaching.
I did suggest an alternative book.
As for your remark, I did teach back in 1998 - 1999 for first year CS students, Pascal and C++.
Re: Learn C and build your own Lisp
#57I am new to programming. What is it so special about Lisp that I keep hearing about it in Hacker's News (often in Machine Learning and from old programmers)?
You will get different answers from different people. There doesn't appear to be any commonly accepted universal truths in Lisp (otherwise we'd all be programming in some variant of it by now). However there are plenty of good ideas which many more popular languages have adopted.
What made it special for me was discovering the link between symbolic computing and the lambda calculus. The kernel at the center of every Lisp is a substrate upon which languages are built. eval knows nothing about your program but can read some Lisp forms and turn itself into a machine that can execute it. This is immensely powerful. From a shockingly small number or primitives you could build, theoretically, any language you need.
The more superficial qualities, for me, are a distinct lack of frivolous, obfuscating syntax; its uniformity; and its direct representation. I don't have to maintain an exhaustive mental mapping of syntactic digraphs and operators, I don't have to remember precedence rules, I don't have to remember the grammatical distinctions between expressions and statements, and I certainly don't have to maintain a running interpreter/compiler in my head. Armed with a simplified mental model of the lambda calculus such as the substitution method is enough to work out what any program is doing (and indeed due to the nature of Lisps is also easy to interactively verify).
Every other language I've worked with requires memorizing a laundry list of special cases and weird rules (ie: how array and pointer parameters are changed by the compiler in C, precedence rules as mentioned, etc) imposed for efficiency's sake and often maligned with good engineering practices. Some strange monkey-brained part of me fools myself into believing I am becoming a better programmer when I pollute my mind with these things... but I've learned over the years that it's just a trick. The ideas are important and the implementation is just the painful cost we pay to make them reality.
Lisp just happens to have the least cognitive load in my case.
Re: Learn C and build your own Lisp
#58Using this guide, is it possible to create a programming language in a non-English language?
Re: Learn C and build your own Lisp
#59I am new to programming. What is it so special about Lisp that I keep hearing about it in Hacker's News (often in Machine Learning and from old programmers)?
Basically Lisp is based on a very different paradigm than most mainstream languages. So if you know Lisp and program in something else, then half of the time you are reminded that the current problem would be really easy in lisp.
Re: Learn C and build your own Lisp
#60I always find it so hard to help out proof-reading code for causes like this. Often, the code is more complicated than I find reasonable, while omitting things that make a lot of sense in "real" code, and it's very hard to know as an outside reader what the exact motivation for each decision was, by the author. A few such things that caused me to WTF: The initial few examples use a pointlessly static and global line…
I would agree, like all code this author definitely has a few quirks about how they write their C code, and I think all of your criticisms are valid. Their readline implementation is definitely sloppy, but they also just throw it in there without really talking about it. Adding to the readline issue, they definitely should have const'd the strings for readline and add_history. It's not just good practice, in this cas…
Well, yes, I know what the strlen() is for, that's why I wrote truncate (not terminate); it is shortening the string by 1 character.
I see two problems with your code: it's over-allocating, since it's going to do the truncation there's no need to add 1 for the termination, it balances out with the newline; and there's absolutely no point in using strcpy() when you know the length.