Programming Assignment I μGo: A Simple Go Programming Language Solution

Description

Your assignment is to write a scanner for the μGo language with lex. This document gives the lexical definition of the language, while the syntactic definition and code generation will follow in subsequent assignments.

Your programming assignments are based around this division and later assignments will use the parts of the system you have built in the earlier assignments. That is, in the first assignment you will implement the scanner using lex, in the second assignment you will implement the syntactic definition in yacc, and in the last assignment you will generate assembly code for the Java Virtual Machine by augmenting your yacc parser.

This definition is subject to modification as the semester progresses. You should take care in implementation that the codes you write are well-structured and able to be revised easily.

1. μGo Language Features

We highlight the features of μGo by comparing it with C language. It is very important to note that μGo is not Go.

μGo is a static type and strong type language.

μGo statements do not end with semicolons ; .

Conditional expression(s) in if and for does not enclosed by parentheses.

μGo does not define while in its language.

/* Example code. */

var a int32 = 3

var b int32 = 1

if a < 3 {

b = 2

}
var sum int32 =	0
var i int32
for i = 0; i <=	10; i++ {
sum += i
}
println(a) //	3
println(b) //	1
println(sum) //	55

2. Lexical Definitions

Tokens are divided into two classes:

tokens that will be passed to the parser, and

tokens that will be discarded by the scanner (e.g., recognized but not passed to the parser).

2.1 Tokens that will be passed to the parser

The following tokens will be recognized by the scanner and will be eventually passed to the parser.

2.1.1 Delimiters

Each of these delimiters should be passed back to the parser as a token.

Delimiters	Symbols
Parentheses	(	){}[]
Semicolon	;
Comma	,
Quotation	“	“
Newline	\n

2.1.2 Arithmetic, Relational, and Logical Operators

Each of these operators should be passed back to the parser as a token.

Operators Symbols

Arithmetic	+	–	*/%++—
Relational	<	>	<= >= == !=
Assignment	=+=–=*=/=%=
Logical	&&		|| !

2.1.3 Keywords

Each of these keywords should be passed back to the parser as a token.

The following keywords are reserved words of μC:

Types	keywords
Data type	int32	float32 bool string
Conditional	if else for
Variable declaration	var
Build-in functions	print	println

2.1.4 Identifiers

An identifier is a string of letters ( a ~ z , A ~ Z , _ ) and digits ( 0 ~ 9 ) and it begins with a letter or underscore. Identifiers are case-sensative; for example, ident , Ident , and IDENT are not the same identifier. Note that keywords are not identifiers.

2.1.5 Integer Literals and Floating-Point Literals

Integer literals: a sequence of one or more digits, such as 1 , 23 , and 666 .

Floating-point literals: numbers that contain floating decimal points, such as 0.2 and 3.141 .

2.1.6 String Literals

A string literal is a sequence of zero or more ASCII characters appearing between double-quote

( “ ) delimiters. A double-quote appearing with a string must be written after a “ , e.g., “abc” and “Hello world” .

2.2 Tokens that will be discarded

The following tokens will be recognized by the scanner, but should be discarded, rather than returning to the parser.

2.2.1 Whitespace

A sequence of blanks (spaces), tabs, and newlines.

2.2.2 Comments

Symbol	Token	Symbol	Token	Symbol	Token
+	ADD	&&	LAND	print	PRINT
–	SUB	||	LOR	println	PRINTLN
*	MUL	!	NOT	if	IF
/	QUO	(	LPAREN	else	ELSE
%	REM	)	RPAREN	for	FOR
++	INC	[	LBRACK	int32	INT
—	DEC	]	RBRACK	float32	FLOAT
>	GTR	{	LBRACE	string	STRING
<	LSS	}	RBRACE	bool	BOOL
>=	GEQ	;	SEMICOLON	true	TRUE
<=	LEQ	,	COMMA	false	FALSE
==	EQL	“	QUOTA	var	VAR
!=	NEQ	\n	NEWLINE

• ASSIGN

+=	ADD_ASSIGN	Int Number	INT_LIT
–=	SUB_ASSIGN	Float	FLOAT_LIT
		Number
*=	MUL_ASSIGN	String Literal	STRING_LIT
/=	QUO_ASSIGN	Identifier	IDENT
%=	REM_ASSIGN	Comment	COMMENT

3.2 Example of Your Scanner Output

The example input code and the corresponding output that we expect your scanner to generate are as follows.

Input:

var a int32 = 3

var b int32

println(a) /* print a */

b += 10 // Hello world

for a < b {

a++

}

Output:

var VAR

• IDENT

int32INT

• ASSIGN

3INT_LIT NEWLINE

var VAR

• IDENT

int32INT NEWLINE

println PRINTLN

• LPAREN

• IDENT

• RPAREN

/* print a */ C Comment

NEWLINE

• IDENT

+= ADD_ASSIGN

10 INT_LIT

// Hello world C++ Comment

NEWLINE

for FOR

• IDENT

• LSS

• IDENT

{LBRACE

NEWLINE

• IDENT

++INC NEWLINE

}RBRACE

Finish scanning,

total line: 7

comment line: 2

4. Environmental Setup

For Linux

Ubuntu 18.04 LTS

Install dependencies: $ sudo apt install flex bison

For Windows

You may like to install VirtualBox to emulate the Linux environment.

Our grading system uses the Ubuntu environment. We will revise your uploaded code to adapt to our environment. In order to facilitate the automated code revision process, we need your help to arrange your code in the following format as specified in 5. Submission.

5. Submission

Upload your homework to Moodle before the deadline.

Deadline: April 23, 2020 at 23:59

Compress your files with zip or rar . Other file formats are not acceptable.

Your uploaded assignment must be organized illustrated below. Otherwise, our auto-grading tool will ignore it.

If our tool fails to recognize your homework files because you do not comply the rules, you will have to live demo your homework with our TAs (after you realize your graded score is unacceptable low) and there will be a 10% discount of your score for this assignment.

As for the filename of your compressed file, you should replace StudentID with your student id number. That is, your compressed file should have the name like: Compiler_F12345678_HW1.zip .

Compiler_StudentID_HW1.zip/

└── Compiler_StudentID_HW1/

├── compiler_hw1.l

└── Makefile

Three steps to create zip file for the submission.

6. References

Source file src/go/token/token.go: https://golang.org/src/go/token/token.go

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