Assignment #1 implement the scanner and parser

COMP 520 Compiler Design
Individual Assignment #1
Language Specifications
Overview
Given the example program sqrt.min and the discussion in class, your first assignment is to
implement the scanner and parser for the MiniLang programming language. Note that as you
design your compiler, some language features may be more difficult to support than you first
thought - or we might have missed out on a key detail that you need. In these cases, bring them
up in class and we can discuss possible changes!
sqrt.min
// Approximate the square root of x
var x: float = 0.0;
var guess: float = 1.0;
var iter: int = 10;
read(x);
while (iter) {
var quot: float = x / guess;
guess = 0.5 * (guess + quot);
iter = iter - 1;
}
print(guess);
print(guess * guess);
Specifications
A program in MiniLang consists of a list of interwoven variable declarations and statements. Note
that the list of declarations and statements may be empty - that is, the empty program, programs
with just declarations, and programs with just statements are valid.
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General
The reserved words may not be used as identifiers, and are case-sensitive.
var string else print
float boolean while true
int if read false
Comments are single line, and start with the double forward slash. There are no block comments.
// This is a comment
Unidentified symbols (those not valid in any token) must cause the program to be rejected. Whitespace (spaces, tables, newlines) is ignored.
Declarations
A variable declaration consists of keyword var, an identifier, the variable type, and an optional initialization. The identifier and type are separated by a colon, and declarations end with semicolons.
var a: float = 0.0;
var b: int;
Types supported by MiniLang are:
• boolean: either true or false
• int: 32-bit integer with no leading zero (unless it is zero)
• float: 32-bit floating point number with digits on both sides of the decimal. (i.e. 3. or .3
are not valid floating point numbers). They may not contain any leading zeros on the LHS
of the decimal, but may have any number of trailing zeros. In other words, the LHS of the
decimal must be a valid integer according to our specification.
– leading: 0.01 is OK, while 000.01 and 01.3 are all errors
– trailing: 0.00000, 0.01000, etc... all OK
• string: a sequence of characters surrounded by quotation marks (i.e. "..."). String literals
may contain the following characters:
– Spaces
– Alphanumerics: [a-zA-Z0-9]
– Symbols: ~ @ # $ % ^ & * - + / ‘ (i.e. backtick) < = |
’ (i.e. singlequote) . , ; : ! ? { } [ ] ( )
– Escape sequences: \a \b \f \n \r \t \v \" \\ (other escape sequences are invalid)
Note that in this language we will accept escaped quotation marks within the string. This
means that "derp\"derp" should be treated as a valid string.
Numeric literals (integers and floatings) do not have a sign - the sign is part of a unary expression.
An identifier must start with either: a letter (uppercase or lowercase) or an underscore. Subsequent
characters can either be letters, underscores, or digits. Identifiers are case sensitive (this will matter
for later phases of the compiler).
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Statements
Statements in the language can be one of the following. Note the first 3 (read, print and assignment) are all terminated by a semicolon. Statement lists (<stmts) are a list of zero or more
statements/declarations (declarations and statements may be interwoven).
• Read into a variable
read(<variable);
• Print an expression
print(<expression);
• Assignment into a variable
<variable = <expression;
• If statement, with 0 or more else-if branches, and an optional else branch
if (<expression) {
<stmts
} [else if (<expression) {
<stmts
}]* [else {
<stmts
}]
• While loop
while (<expression) {
<stmts
}
Expressions
Expressions follow typical math notation found in modern programming languages, and consist of:
• Binary operations: +, -, *, /, ==, !=, =, <=, , <, &&, ||
• Unary operations: - (i.e. -3 is a valid expression), !
• Matched parentheses
• Left associativity for all operators
• Precedence (highest to lowest)
– Unary operators
– Typical math precedence of operations for math operators
– Comparison operators (=, <=, , <)
– Relational operators (== and !=)
– Logical and (&&)
– Logical or (||)
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