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PL/0 @ NUAA CCST 2020 Compiler Principles

Content

PL/0 compiler and virtual machine

This is a course design for Compiler Principles of NUAA CCST 2020. It includes a PL/0 bytecode compiler and virtual machine.

This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.

What is LL(1)?

LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.

Look at the following grammar:

<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]

As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?

And abviously, <condition> alawys starts with "if", and <loop> always starts with "while". So the answer is:

if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}

And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).

For LL(k), k means some of the rules are determined by the next k(by maximum) tokens. In fact most of the languages used in the industry are LL(1) with some special cases. And of course, some of these languages are LL(k). Languages using LL grammar are usually easier to maintain.

But LL(1) only requires one token lookahead. So it is easy to implement the parser.

What is PL/0?

PL/0 is a simple language. It is a subset of Pascal. The grammar is really simple, so it only requires LL(1) parser. Here's the grammar:

<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>

Build

use this command to compile this project:

make

Usage

To get help:

./pl0 -h

use this command to use pl0 interpreter:

./pl0 -exec <filename>

use this command to use pl0 interpreter(debug):

./pl0 -debug <filename>

About

PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles

Topics

compilercompiler-principlesnuaa

Resources

Readme
Activity

Stars

38 stars

Watchers

1 watching

Forks

5 forks
Report repository

Releases

Packages

Contributors

Languages

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})();
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try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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PL/0 @ NUAA CCST 2020 Compiler Principles
Content
PL/0 compiler and virtual machine
This is a course design for Compiler Principles of NUAA CCST 2020.
It includes a PL/0 bytecode compiler and virtual machine.
This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.
What is LL(1)?
LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.
Look at the following grammar:
<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]
As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?
And abviously, <condition> alawys starts with "if",
and <loop> always starts with "while". So the answer is:
if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}
And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).
For LL(k), k means some of the rules are determined by the next k(by maximum) tokens.
In fact most of the languages used in the industry are LL(1) with some special cases.
And of course, some of these languages are LL(k).
Languages using LL grammar are usually easier to maintain.
But LL(1) only requires one token lookahead.
So it is easy to implement the parser.
What is PL/0?
PL/0 is a simple language. It is a subset of Pascal.
The grammar is really simple, so it only requires LL(1) parser.
Here's the grammar:
<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>
Build
use this command to compile this project:
make
Usage
To get help:
./pl0 -h
use this command to use pl0 interpreter:
./pl0 -exec <filename>
use this command to use pl0 interpreter(debug):
./pl0 -debug <filename>
About
PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles
Topics
compilercompiler-principlesnuaa
Resources
Readme
Activity
Stars
38 stars
Watchers
1 watching
Forks
5 forks
Report repository
Releases
Packages
Contributors
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, 'i');
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var __re = new RegExp('^' + ".*" + '

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PL/0 @ NUAA CCST 2020 Compiler Principles
Content
PL/0 compiler and virtual machine
This is a course design for Compiler Principles of NUAA CCST 2020.
It includes a PL/0 bytecode compiler and virtual machine.
This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.
What is LL(1)?
LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.
Look at the following grammar:
<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]
As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?
And abviously, <condition> alawys starts with "if",
and <loop> always starts with "while". So the answer is:
if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}
And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).
For LL(k), k means some of the rules are determined by the next k(by maximum) tokens.
In fact most of the languages used in the industry are LL(1) with some special cases.
And of course, some of these languages are LL(k).
Languages using LL grammar are usually easier to maintain.
But LL(1) only requires one token lookahead.
So it is easy to implement the parser.
What is PL/0?
PL/0 is a simple language. It is a subset of Pascal.
The grammar is really simple, so it only requires LL(1) parser.
Here's the grammar:
<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>
Build
use this command to compile this project:
make
Usage
To get help:
./pl0 -h
use this command to use pl0 interpreter:
./pl0 -exec <filename>
use this command to use pl0 interpreter(debug):
./pl0 -debug <filename>
About
PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles
Topics
compilercompiler-principlesnuaa
Resources
Readme
Activity
Stars
38 stars
Watchers
1 watching
Forks
5 forks
Report repository
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Packages
Contributors
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, 'i');
if (__m === '*' || __re.test(location.href)) {
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var ref = document.referrer;
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function highlight(node) {
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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PL/0 @ NUAA CCST 2020 Compiler Principles
Content
PL/0 compiler and virtual machine
This is a course design for Compiler Principles of NUAA CCST 2020.
It includes a PL/0 bytecode compiler and virtual machine.
This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.
What is LL(1)?
LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.
Look at the following grammar:
<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]
As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?
And abviously, <condition> alawys starts with "if",
and <loop> always starts with "while". So the answer is:
if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}
And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).
For LL(k), k means some of the rules are determined by the next k(by maximum) tokens.
In fact most of the languages used in the industry are LL(1) with some special cases.
And of course, some of these languages are LL(k).
Languages using LL grammar are usually easier to maintain.
But LL(1) only requires one token lookahead.
So it is easy to implement the parser.
What is PL/0?
PL/0 is a simple language. It is a subset of Pascal.
The grammar is really simple, so it only requires LL(1) parser.
Here's the grammar:
<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>
Build
use this command to compile this project:
make
Usage
To get help:
./pl0 -h
use this command to use pl0 interpreter:
./pl0 -exec <filename>
use this command to use pl0 interpreter(debug):
./pl0 -debug <filename>
About
PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles
Topics
compilercompiler-principlesnuaa
Resources
Readme
Activity
Stars
38 stars
Watchers
1 watching
Forks
5 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
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'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
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var changed = false;
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} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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PL/0 @ NUAA CCST 2020 Compiler Principles
Content
PL/0 compiler and virtual machine
This is a course design for Compiler Principles of NUAA CCST 2020.
It includes a PL/0 bytecode compiler and virtual machine.
This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.
What is LL(1)?
LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.
Look at the following grammar:
<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]
As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?
And abviously, <condition> alawys starts with "if",
and <loop> always starts with "while". So the answer is:
if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}
And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).
For LL(k), k means some of the rules are determined by the next k(by maximum) tokens.
In fact most of the languages used in the industry are LL(1) with some special cases.
And of course, some of these languages are LL(k).
Languages using LL grammar are usually easier to maintain.
But LL(1) only requires one token lookahead.
So it is easy to implement the parser.
What is PL/0?
PL/0 is a simple language. It is a subset of Pascal.
The grammar is really simple, so it only requires LL(1) parser.
Here's the grammar:
<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>
Build
use this command to compile this project:
make
Usage
To get help:
./pl0 -h
use this command to use pl0 interpreter:
./pl0 -exec <filename>
use this command to use pl0 interpreter(debug):
./pl0 -debug <filename>
About
PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles
Topics
compilercompiler-principlesnuaa
Resources
Readme
Activity
Stars
38 stars
Watchers
1 watching
Forks
5 forks
Report repository
Releases
Packages
Contributors
Languages

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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PL/0 @ NUAA CCST 2020 Compiler Principles
Content
PL/0 compiler and virtual machine
This is a course design for Compiler Principles of NUAA CCST 2020.
It includes a PL/0 bytecode compiler and virtual machine.
This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.
What is LL(1)?
LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.
Look at the following grammar:
<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]
As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?
And abviously, <condition> alawys starts with "if",
and <loop> always starts with "while". So the answer is:
if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}
And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).
For LL(k), k means some of the rules are determined by the next k(by maximum) tokens.
In fact most of the languages used in the industry are LL(1) with some special cases.
And of course, some of these languages are LL(k).
Languages using LL grammar are usually easier to maintain.
But LL(1) only requires one token lookahead.
So it is easy to implement the parser.
What is PL/0?
PL/0 is a simple language. It is a subset of Pascal.
The grammar is really simple, so it only requires LL(1) parser.
Here's the grammar:
<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>
Build
use this command to compile this project:
make
Usage
To get help:
./pl0 -h
use this command to use pl0 interpreter:
./pl0 -exec <filename>
use this command to use pl0 interpreter(debug):
./pl0 -debug <filename>
About
PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles
Topics
compilercompiler-principlesnuaa
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38 stars
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1 watching
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, 'i');
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// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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PL/0 @ NUAA CCST 2020 Compiler Principles
Content
PL/0 compiler and virtual machine
This is a course design for Compiler Principles of NUAA CCST 2020.
It includes a PL/0 bytecode compiler and virtual machine.
This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.
What is LL(1)?
LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.
Look at the following grammar:
<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]
As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?
And abviously, <condition> alawys starts with "if",
and <loop> always starts with "while". So the answer is:
if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}
And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).
For LL(k), k means some of the rules are determined by the next k(by maximum) tokens.
In fact most of the languages used in the industry are LL(1) with some special cases.
And of course, some of these languages are LL(k).
Languages using LL grammar are usually easier to maintain.
But LL(1) only requires one token lookahead.
So it is easy to implement the parser.
What is PL/0?
PL/0 is a simple language. It is a subset of Pascal.
The grammar is really simple, so it only requires LL(1) parser.
Here's the grammar:
<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>
Build
use this command to compile this project:
make
Usage
To get help:
./pl0 -h
use this command to use pl0 interpreter:
./pl0 -exec <filename>
use this command to use pl0 interpreter(debug):
./pl0 -debug <filename>
About
PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles
Topics
compilercompiler-principlesnuaa
Resources
Readme
Activity
Stars
38 stars
Watchers
1 watching
Forks
5 forks
Report repository
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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PL/0 @ NUAA CCST 2020 Compiler Principles
Content
PL/0 compiler and virtual machine
This is a course design for Compiler Principles of NUAA CCST 2020.
It includes a PL/0 bytecode compiler and virtual machine.
This repo was used to store the code, but now let's make it more useful. This repo will help you to learn a simple implementation of compiler of a simple language PL/0, which uses LL(1) grammar.
What is LL(1)?
LL(1) grammar means that every production rule can be determined by the first symbol of itself. To make it more understandable, we can use a simple example to illustrate it.
Look at the following grammar:
<code_block>::="begin" {<stmt>} "end"<stmt>::= <condition> | <loop>
<loop>::="while" <expr> "do" <code_block>
<condition>::="if" <expr> "then" <code_block> ["else" <code_block>]
As we could see, <stmt> accept two kinds of statement: <condition> and <loop>. But how to distinguish them?
And abviously, <condition> alawys starts with "if",
and <loop> always starts with "while". So the answer is:
if (lookahead(tok_kind::keyword_if)) {
// parse <condition>
} elseif (lookahead(tok_kind::keyword_while)) {
// parse <loop>
}
And we could see that we could use lookahead() to check the next 1 token, then we will definitely know what kind of statement we will parse. That's what 1 means in LL(1).
For LL(k), k means some of the rules are determined by the next k(by maximum) tokens.
In fact most of the languages used in the industry are LL(1) with some special cases.
And of course, some of these languages are LL(k).
Languages using LL grammar are usually easier to maintain.
But LL(1) only requires one token lookahead.
So it is easy to implement the parser.
What is PL/0?
PL/0 is a simple language. It is a subset of Pascal.
The grammar is really simple, so it only requires LL(1) parser.
Here's the grammar:
<program>::="program" <id> ";" <block>
<decl>::= <var-decl>
| <const-decl>
| <procedure-decl>
<var-decl>::="var" <id> [":=" <expr>] ";"<const-decl>::="const" <id> [":=" <expr>] {"," <id> [":=" <expr>]} ";"<procedure-decl>::="procedure" <id> "(" [<param-list>] ")"";" <block>
<param-list>::= <id> {"," <id>}
<block>= {<decl>} <body>
<body>="begin" <stmt> {";" <stmt>} "end"<stmt>::= <assign-stmt>
| <if-stmt>
| <while-stmt>
| <call-stmt>
| <read-stmt>
| <write-stmt>
| <block>
<assign-stmt>::= <id> ":=" <expr>
<if-stmt>::="if" <expr> "then" <stmt> [ "else" <stmt> ]
<while-stmt>::="while" <expr> "do" <stmt>
<call-stmt>::="call" <id> "(" [<actual-param-list>] ")"<actual-param-list>::= <expr> {"," <expr>}
<read-stmt>::="read""(" <id> {"," <id>} ")"<write-stmt>::="write""(" [<expr> {"," <expr>}] ")"<expr>::= <term> {("+"|"-") <term>}
<term>::= <factor> {("*"|"/") <factor>}
<factor>::= <id>
| <number>
|"(" <expr> ")"|"-" <factor>
Build
use this command to compile this project:
make
Usage
To get help:
./pl0 -h
use this command to use pl0 interpreter:
./pl0 -exec <filename>
use this command to use pl0 interpreter(debug):
./pl0 -debug <filename>
About
PL/0 compiler & vm, course design for NUAA CCST 2020 Compiler Principles
Topics
compilercompiler-principlesnuaa
Resources
Readme
Activity
Stars
38 stars
Watchers
1 watching
Forks
5 forks
Report repository
Releases
Packages
Contributors
Languages