The Language N
MUST compiler course Fall 2019
Instructor: Zhiyao Liang
1. Motifation
We design a language that can do simple calculation of numbers, therefore the name N.
2. Language features 2.1 Comments
/* some comments */
Same as in C.
2.2 Basic data type
Number A num constant is a fraction, which is a pair of integers. For example: means the integer 3
means the fraction 3/5 is the same as 5:1
are number with signs. Address of num: num *
An address of deeper levels, such as address of address, is not allowed. String:
num
3|1
3|5
5
+5
A string constant is in the form of
A string constant is only used by the built-in function There is no variable for string.
2.3 Array:
Same as C. For example:
.
.
num arr[9];
num * arr[9];
-3|5
“some string here”
is a statement that declares an array of 9 elements with type num. declares an array of 9 addresses of num.
output_string
Nested array is not allowed.
2.4 Function:
The syntax of functions are very similar to C. return type: <\br>
num *
parameter type:
num *
The function definition has the following form:
The body of a function definition is a sequence of statements, that does not contain another function definition.
A smile face 🙂 marks the end of the body of a function definition
A function call is the same as in C, like max(x, 3|5) 2.5 Selection
if statement. It optionally has an else part. 2.6 Loop
while statement 2.7 Operators
Arithmetic operators:
The modular operator is not defined when the operands are not both integers. (Integers are fractions with the denominator as 1). Or you can define the modulo computation with fractions [1].
void
num
void
num
returnType functionName (parameters) –>
statements
🙂
+-*/%
%
Relational operators: > < >= == != The result is 0 or 1.
Logical operators: . The result is 0 or 1.
Address operator: . This operator can be applied to a variable of num and return the address of num .
Index operator: []
Assignment operator: =
The precedence, associativity, and arity (number of operands), and meaning of these operators are the same as in C. The result of an expression applying an operator is always a num .
Input and Output
The prototypes of these built-in functions are listed below.
void print(str) Here the type str represent some string constant. str is not used explicitly as a type in the language N.
Expression
An expression is one of the following kind:
A constant: like 3|5 A variable: like
The naming policy of a variable is the same as in C: a sequence of letters, numbers, and
underscore _ , while the starting character is a letter of underscore.
An operator expression, where some operator is applied (operators are discussed above). An expression wrapped by parenthesis, like: ( some_exp ) .
Statement
A statement can be one of the following kind:
A simple statement which ending with a , like:
&& || !
num read(void)
void write(num)
5
x
num arr[8]; /*array declaration */
;
num x; /* variable declaration */
void fun(num x); /*function declaration */
x = y + 3; /* expression statement */
somefunction(void);
&
/* function call, another kind of expression statement*/
if statement
statement
compound statement, which is a block with { and } at the two ends. function definition, which also be called a function statement.
keywords
while if else return num
Program
A program is a sequence of statements that are executed consequently. Unlike as C, there no need to have a main function as the entrance of a program. The execution of a program starts at the first statement.
Program example.
There are several .n files in the folder N_Program_examples . References
1. “Is it possible to do modulo of a fraction” https://math.stackexchange.com/questions/864568/is- it-possible-to-do-modulo-of-a-fraction
while