Programming Assignment I μGo: A Simple Go Programming Language Solution

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:

1
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



2
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

Comments can be added in several ways:

C-style is texts surrounded by /* and */ C++-style comments are a text following a



delimiters, which may span more than one line;

    • delimiter running up to the end of the line.


Whichever comment style is encountered first remains in effect until the appropriate comment close is encountered. For example,

    • this is a comment // line */ /* with /* delimiters */ before the end

and


/* this is a comment // line with some /* and C delimiters */

are both valid comments.

2.2.3 Other characters

The undefined characters or strings should be discarded by your scanner during parsing.

3. What should Your Scanner Do?


3.1 Assignment Requirements

We have prepared 11 μGo programs, which are used to test the functionalities of your scanner.

Each test program is 10pt and the total score is 110pt. You will get 110pt if your scanner successfully generates the answers for all eleven programs.

The output messages generated by your scanner must use the given names of token classes listed below.





3

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

4
    • 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.


5
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
































6