I love this book! I worked through a bunch of it during my winter break last year and found the incremental teaching style extremely rewarding. For readers of the book, Sandler’s reference OCaml implementation is super useful for getting your bearings. I was kind of thrown off by the use of TACKY as an IR, but it was nice to have a solid reference as I worked through the book. For those more experienced with compilers: what are some good resources for stuff like SSA and optimisation? I’ve looked at some of the resources here https://bernsteinbear.com/pl-resources/ but are there other canonical resources?
You can choose to implement it differently based on your implementation language. Data Classes and If statements work really for this in Python, for example.
This part confused me quite a bit so I turned it into the more verbose format by copy-pasting. I don’t like the boilerplate code generation either so I converted that part too. The whole book is still pretty interesting though.
It probably has nothing to do with recursive descent parsing, which is intuitive, but with the visitor pattern as mentioned. I myself find it very distracting too.
The visitor pattern is a technique for dynamic dispatch on two values (typically one represents 'which variant of data are we working with' and the other 'which operation are we performing'). You would not generally use that in recursive descent parsing, because when parsing you don't have an AST yet, so 'which variant of data' doesn't make sense, you are just consuming tokens from a stream.
My guy... Do you think that parsers just like... concat tokens into tuples or something....??? Do you not understand that after lexing you have tokens (which are a "type") and AST node construction (an "operation") and that the grammar of a language is naturally a graph.... Like where else would you get the "recursion" from....
If that doesn't make sense I invite you to read some literature:
> makeAST():
> asks the tokenizer for the next token t, and then asks t to call the appropriate factory method the int token and the id token call makeLeaf(), the left parenthesis token calls makeBinOp() all other tokens should flag an error! does the above "smell" like the visitor pattern to you or not? Who are the hosts and who are the visitors?
> The crafting interpreting asks the reader to use the visitor pattern...
...or just a big old, plain jane switch statement.
In my current project I modified my ASDL generator to output a C instead of C++ AST and the visitor pattern carried over until realizing a switch statement is just as good (or better) in C so I ripped out that part of the template file. The choice was to write a dispatch function which called the various methods based on the AST node type or have a generated struct full of function pointers with a generated dispatch function which calls the various methods based on the AST node type. Same difference, really, just one has an added level of indirection.
The amazing part is I didn't rewrite the ASDL generator for the fifth time and just decided it's 'good enough' for what I need it for. Aside from one small C++ism, which is easily worked around and turns out wasn't even needed in the C++ template, the thing is 100% language and 'access pattern' agnostic in generating the output code.
There was probably a point I was trying to make when I started typing, dunno?
- You don't need a visitor pattern if you have predetermined the data you are going to work with and all the operations on it (i.e., the open/closed principle does not apply.)
- For the same reason, you don't need dynamic dispatch, which is often how the visitor (and other) pattern(s) are implemented.
- The code is much simpler to understand (and debug) because it's all there in once place. It's also faster than the dynamic dispatch version because it's all known at compile-time.
- Personally: OOP is stupid, confusing, and inefficient; I think universities should only teach it as an optional course. These patterns are 50% lack of functional programming features and 50% sheer stupidity. Universities should go back to teaching real abstraction with Scheme and SICP, a MIPS-style assembly language, and stop confusing students.
I love this book! I worked through a bunch of it during my winter break last year and found the incremental teaching style extremely rewarding. For readers of the book, Sandler’s reference OCaml implementation is super useful for getting your bearings. I was kind of thrown off by the use of TACKY as an IR, but it was nice to have a solid reference as I worked through the book. For those more experienced with compilers: what are some good resources for stuff like SSA and optimisation? I’ve looked at some of the resources here https://bernsteinbear.com/pl-resources/ but are there other canonical resources?
From what the blog author says (I haven’t looked into the book), the approach reminds me of
> Abdulaziz Ghuloum, 2006, An Incremental Approach to Compiler Construction http://scheme2006.cs.uchicago.edu/11-ghuloum.pdf
Oh that’s exactly what the book’s author blog mentions: https://norasandler.com/2017/11/29/Write-a-Compiler.html
You can also find this approach in this book that comes in Racket and Python flavors [0].
[0] https://mitpress.mit.edu/9780262047760/essentials-of-compila...
The author of the book also has a series of blog entries: https://norasandler.com/2017/11/29/Write-a-Compiler.html
This makes the book sound very well structured! I also found Ghuloum's paper inspirational.
Sounds like a great book. I worked through nand2tetris ages ago and remember enjoying it as well.
The crafting interpreting asks the reader to use the visitor pattern, and this was quite a turn off for me, I stopped there.
You can choose to implement it differently based on your implementation language. Data Classes and If statements work really for this in Python, for example.
Statement Data Classes: https://github.com/alabhyajindal/plox/blob/main/stmt.py
If statements in the parser matching against them: https://github.com/alabhyajindal/plox/blob/main/parser.py#L3...
This part confused me quite a bit so I turned it into the more verbose format by copy-pasting. I don’t like the boilerplate code generation either so I converted that part too. The whole book is still pretty interesting though.
Couldn't you write the interpreter without it?
Lolol weirdest reason to reject that book - 90% of production parsers are recursive descent parsers.
It probably has nothing to do with recursive descent parsing, which is intuitive, but with the visitor pattern as mentioned. I myself find it very distracting too.
.... They're the same thing....
What?
The visitor pattern is a technique for dynamic dispatch on two values (typically one represents 'which variant of data are we working with' and the other 'which operation are we performing'). You would not generally use that in recursive descent parsing, because when parsing you don't have an AST yet, so 'which variant of data' doesn't make sense, you are just consuming tokens from a stream.
> you are just consuming tokens from a stream.
My guy... Do you think that parsers just like... concat tokens into tuples or something....??? Do you not understand that after lexing you have tokens (which are a "type") and AST node construction (an "operation") and that the grammar of a language is naturally a graph.... Like where else would you get the "recursion" from....
If that doesn't make sense I invite you to read some literature:
> makeAST():
> asks the tokenizer for the next token t, and then asks t to call the appropriate factory method the int token and the id token call makeLeaf(), the left parenthesis token calls makeBinOp() all other tokens should flag an error! does the above "smell" like the visitor pattern to you or not? Who are the hosts and who are the visitors?
https://www.clear.rice.edu/comp212/02-fall/labs/11/
> The crafting interpreting asks the reader to use the visitor pattern...
...or just a big old, plain jane switch statement.
In my current project I modified my ASDL generator to output a C instead of C++ AST and the visitor pattern carried over until realizing a switch statement is just as good (or better) in C so I ripped out that part of the template file. The choice was to write a dispatch function which called the various methods based on the AST node type or have a generated struct full of function pointers with a generated dispatch function which calls the various methods based on the AST node type. Same difference, really, just one has an added level of indirection.
The amazing part is I didn't rewrite the ASDL generator for the fifth time and just decided it's 'good enough' for what I need it for. Aside from one small C++ism, which is easily worked around and turns out wasn't even needed in the C++ template, the thing is 100% language and 'access pattern' agnostic in generating the output code.
There was probably a point I was trying to make when I started typing, dunno?
My takeaway from your verbose description is:
- You don't need a visitor pattern if you have predetermined the data you are going to work with and all the operations on it (i.e., the open/closed principle does not apply.)
- For the same reason, you don't need dynamic dispatch, which is often how the visitor (and other) pattern(s) are implemented.
- The code is much simpler to understand (and debug) because it's all there in once place. It's also faster than the dynamic dispatch version because it's all known at compile-time.
- Personally: OOP is stupid, confusing, and inefficient; I think universities should only teach it as an optional course. These patterns are 50% lack of functional programming features and 50% sheer stupidity. Universities should go back to teaching real abstraction with Scheme and SICP, a MIPS-style assembly language, and stop confusing students.
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