How would I go about writing an interpreter in C?
I'd love some references, or tips, possibly an e-book or two. I'm not looking to write a compiler, just looking for a tutorial I could follow along and modify as I go. Thank you for being understanding!
BTW: It must be C.
Any more replies would be appreciated.
Answer
A great way to get started writing an interpreter is to write a simple machine simulator. Here's a simple language you can write an interpreter for:
The language has a stack and 6 instructions:
push <num> # push a number on to the stack
pop # pop off the first number on the stack
add # pop off the top 2 items on the stack and push their sum on to the stack. (remember you can add negative numbers, so you have subtraction covered too). You can also get multiplication my creating a loop using some of the other instructions with this one.
ifeq <address> # examine the top of the stack, if it's 0, continue, else, jump to <address> where <address> is a line number
jump <address> # jump to a line number
print # print the value at the top of the stack
dup # push a copy of what's at the top of the stack back onto the stack.
Once you've written a program that can take these instructions and execute them, you've essentially created a very simple stack based virtual machine. Since this is a very low level language, you won't need to understand what an AST is, how to parse a grammar into an AST, and translate it to machine code, etc. That's too complicated for a tutorial project. Start with this, and once you've created this little VM, you can start thinking about how you can translate some common constructs into this machine. e.g. you might want to think about how you might translate a C if/else statement or while loop into this language.
Edit:
From the comments below, it sounds like you need a bit more experience with C before you can tackle this task.
What I would suggest is to first learn about the following topics:
- scanf, printf, putchar, getchar - basic C IO functions
- struct - the basic data structure in C
- malloc - how to allocate memory, and the difference between stack memory and heap memory
- linked lists - and how to implement a stack, then perhaps a binary tree (you'll need to understand structs and malloc first)
Then it'll be good to learn a bit more about the string.h library as well - strcmp, strdup - a couple useful string functions that will be useful.
In short, C has a much higher learning curve compared to python, just because it's a lower level language and you have to manage your own memory, so it's good to learn a few basic things about C first before trying to write an interpreter, even if you already know how to write one in python.