Format fixes in 1996/august
I am aware, however, of at least one possible bug. I've not addressed this or put it in bugs.md. I will first look at it a bit more as at first in linux I got a segfault but then I had the same problem under macOS - a freeze. I want to see if I can duplicate the crash again before I write about any bugs.
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@@ -1,3 +1,6 @@
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august
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august.oc
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test.oo
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fac.oo
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parse.oo
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prog.oc
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+134
-94
@@ -1,65 +1,85 @@
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# Best of Show
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Lennart Augustsson
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CR&T
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Stora Badhusgatan 18-20
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S-411 21 Goteborg
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Sweden
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Lennart Augustsson
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CR&T
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Stora Badhusgatan 18-20
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S-411 21 Goteborg
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Sweden
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## To build:
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make all
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```sh
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make all
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```
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## To run:
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cat august.c test.oc | ./august > test.oo
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./august < test.oo
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```sh
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cat august.c test.oc | ./august > test.oo
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./august < test.oo
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```
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NOTE: Some compilers will compile this code into infinite loops!
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If the above cat line does not execute in a very short amount
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of time, then you may need to fix your compiler or use gcc.
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It should print a `!` followed by a newline.
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NOTE: Some compilers will compile this code into infinite loops!
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If the above cat line does not execute in a very short amount
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of time, then you may need to fix your compiler or use gcc.
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## Try:
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cat august.c fac.oc | ./august > fac.oo
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./august < fac.oo
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```sh
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cat august.c fac.oc | ./august > fac.oo
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./august < fac.oo
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cat august.c fac.oc | ./august | ./august
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cat august.c fac.oc | ./august | ./august
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cat august.c parse.oc | ./august > parse.oo
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cat parse.oo fac.oc | ./august | ./august
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cat august.c parse.oc | ./august > parse.oo
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cat parse.oo fac.oc | ./august | ./august
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```
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## Judges' remarks:
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This entry can feed on itself. If you C preprocess the source,
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This entry can feed on itself. If you C pre-process the source,
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you compile the interpreter:
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make august.oc
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```sh
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make august.oc
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```
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We can now compile the interpreter as follows:
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cat august.c august.oc | ./august > august.oo
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```sh
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cat august.c august.oc | ./august > august.oo
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```
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and use the compiled interpreter to execute some previously
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compiled code:
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cat august.oo test.oo | ./august
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```sh
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cat august.oo test.oo | ./august
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```
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And we can have the compiled interpreter interpret itself which
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in turn compiles the test program:
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cat august.oo august.oo fac.oo | ./august
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```sh
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cat august.oo august.oo fac.oo | ./august
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```
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And if you have lots of spare time, you can recurse one level deeper:
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cat august.oo august.oo august.oo fac.oo | ./august
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```sh
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cat august.oo august.oo august.oo fac.oo | ./august
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```
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We (the judges) recommend that you spend some time studying this
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entry as it surely will make the 'best of the IOCCC' list. It was
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very well received by those who attended the IOCCC BOF.
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## Author's remarks
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## Author's remarks:
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This program is a bytecode interpreter. This fact is not
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particularly obfuscated; any experienced C programmer can see that
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@@ -86,70 +106,88 @@ The compiler has absolutely no error checking, so things
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can go wrong. But this is what seasoned C programmers are used to.
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Assume that the interpreter has been compiled (source in prog.c and
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binary in prog) and that we have this in a file named test.oc:
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binary in prog) and that we have this in a file named `test.oc`:
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main() { putchar('!'); putchar('\n'); exit(0); }
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```
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main() { putchar('!'); putchar('\n'); exit(0); }
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```
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We can then compile by
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cat august.c test.oc | ./august > test.oo
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```sh
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cat august.c test.oc | ./august > test.oo
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```
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And run the compiled program by
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./august < test.oo
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```sh
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./august < test.oo
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```
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Or even simpler:
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cat august.c test.oc | ./august | ./august
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A larger example is included fac.oc.
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```sh
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cat august.c test.oc | ./august | ./august
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```
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The compiler for OC is naturally written in OC (where did you think
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the byte code came from?). It is in the file parse.oc.
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A larger example is included [fac.oc](fac.oc).
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Hmm... So now we have an interpreter written in OC and a compiler
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for OC, can we compile the interpreter? Yes, we can! The OC
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compiler does not have a preprocessor (hey, what do you expect from
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a program that is this small), so we need to use an external one.
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To preprocess august.c use the command from the build file, but add
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the -E flag and change 60000 to 40000, i.e.:
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The compiler for OC is naturally written in OC (where did you think the byte
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code came from?). It is in the file [parse.oc](parse.oc).
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cc -E -DZ=40000 .... august.c > prog.oc
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Hmm... So now we have an interpreter written in OC and a compiler for OC, can
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we compile the interpreter? Yes, we can! The OC compiler does not have a
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preprocessor (hey, what do you expect from a program that is this small), so we
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need to use an external one. To pre-process [august.c](august.c) use the
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command from the Makefile, but add the `-E` flag and change 60000 to 40000,
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i.e.:
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If prog.oc contain some junk line starting with a `#' (most likely
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```sh
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cc -E -DZ=40000 .... august.c > prog.oc
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```
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If `prog.oc` contain some junk line starting with a `#' (most likely
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it does) then remove it.
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OK, we can now compile the interpreter:
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cat august.c prog.oc | ./august > prog.oo
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```sh
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cat august.c prog.oc | ./august > prog.oo
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```
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And we can run it:
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cat prog.oo test.oo | ./august
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```sh
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cat prog.oo test.oo | ./august
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```
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Here we have the interpreter interpreting another interpreter that runs
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the program. Did you think that was too fast? Just throw in another
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level of interpretation:
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cat prog.oo prog.oo test.oo | ./august
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```sh
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cat prog.oo prog.oo test.oo | ./august
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```
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And another...
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cat prog.oo prog.oo prog.oo test.oo | ./august
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```sh
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cat prog.oo prog.oo prog.oo test.oo | ./august
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```
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*****
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---
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Fitting the byte code for the compiler into the initial comment
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was a challenge. I had to strip the compiler/interpreter of
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a lot of functionality to bring down their sizes. The initial
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version had a full set of binary operators as well as prefix &.
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version had a full set of binary operators as well as prefix `&`.
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Given a handful more bytes it would be easy to put them back.
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Anyway, the bytecode from the compiler is first optimized in
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an external optimizer (not supplied here); this brings down the
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size of it by about 30%. The remaining code is then LZ-compressed
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(roughly) with a sliding window of 255 bytes. The most common
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occuring bytes are then encoded using " \n\t;{}" to avoid having
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occuring bytes are then encoded using `" \n\t;{}"` to avoid having
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them counted as significant. About 200 bytes of the interpreter
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handles the unpacking of the byte code (this is a lot, but it pays
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off).
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@@ -161,75 +199,77 @@ coder), but decompression then takes up too much code. Maybe this
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would be a way to fit it all into the 1536 bytes, but I'm don't have
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time to try it.
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*****
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---
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Execution starts at main(). Nothing can be used before it is
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defined. getchar() and putchar() are predefined functions.
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Execution starts at `main()`. Nothing can be used before it is
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defined. `getchar()` and `putchar()` are predefined functions.
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The following is a description of the OC grammar:
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Below is a description of the OC grammar.
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OC grammar
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==========
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### OC grammar
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Terminals are in quotes, () is used for bracketing.
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Terminals are in quotes, `()` is used for bracketing.
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program: decl*
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```
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program: decl*
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decl: vardecl
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fundecl
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decl: vardecl
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fundecl
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vardecl: type NAME ;
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type NAME "[" INT "]" ;
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vardecl: type NAME ;
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type NAME "[" INT "]" ;
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fundecl: type NAME "(" args ")" "{" body "}"
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fundecl: type NAME "(" args ")" "{" body "}"
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args: /*empty*/
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( arg "," )* arg
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args: /*empty*/
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( arg "," )* arg
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arg: type NAME
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arg: type NAME
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body: vardecl* stmt*
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body: vardecl* stmt*
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stmt: ifstmt
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whilestmt
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dowhilestmt
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"return" expr ";"
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expr ";"
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"{" stmt* "}"
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";"
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stmt: ifstmt
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whilestmt
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dowhilestmt
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"return" expr ";"
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expr ";"
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"{" stmt* "}"
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";"
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ifstmt: "if" "(" expr ")" stmt
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"if" "(" expr ")" stmt "else" stmt
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ifstmt: "if" "(" expr ")" stmt
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"if" "(" expr ")" stmt "else" stmt
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whilestmt: "while" "(" expr ")" stmt
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whilestmt: "while" "(" expr ")" stmt
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dowhilestmt: "do" stmt "while" "(" expr ")" ";"
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dowhilestmt: "do" stmt "while" "(" expr ")" ";"
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expr: expr binop expr
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unop expr
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expr "[" expr "]"
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"(" expr ")"
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expr "(" exprs ")"
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NAME
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INT
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CHAR
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STRING
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expr: expr binop expr
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unop expr
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expr "[" expr "]"
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"(" expr ")"
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expr "(" exprs ")"
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NAME
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INT
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CHAR
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STRING
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exprs: /*empty*/
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(expr ",")* expr
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exprs: /*empty*/
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(expr ",")* expr
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binop: "+" | "-" | "*" | "/" | "%" |
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"=" |
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"<" | "==" | "!="
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binop: "+" | "-" | "*" | "/" | "%" |
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"=" |
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"<" | "==" | "!="
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unop: "!" | "-" | "*"
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unop: "!" | "-" | "*"
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type: "int" stars
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"char" stars
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type: "int" stars
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"char" stars
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stars: "*"*
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stars: "*"*
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*****
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```
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---
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Well, that is enough ranting for now.
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Reference in new issue
Block a user