Assignment #2 implement the relevant semantics




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COMP 520 Compiler Design
Individual Assignment #2

Given the lexical and syntactic choices from the first assignment, your second assignment is to
implement the relevant semantics for each language construct. Note that as you implement your
compiler, some decisions may be more difficult to implement than you first thought – or we might
have missed out a key detail you need. In these cases, bring them up in class and we can discuss
possible changes. By the end of this assignment you will have produced your first full compiler!
A program in MiniLang consists of a list of interwoven variable declarations and statements.
Variable declarations must follow the following rules or emit a compile time error “Error: <description”.
• Variable identifiers must be defined before being used
var a : int;
b = 5; // Error: (line 2) “b” is not declared
• Variable identifiers must not be redeclared (regardless of type)
var a : int;
var a : int; // Error: (line 2) “a” is already declared
• Variable identifiers follow typical static nested scoping rules. Identifiers may be re-declared in
nested scopes and shadow parent declarations, but are not visible in sibling or parent scopes.
var a : int;
if (true) {
var a : float;
a = 5.0; // Uses the inner-most declaration (float)
var b : int;
b = 5; // Error: (line 7) “b” is not declared
For this assignment, we will be using the following types from C
• Integers: int
• Float: float
• Strings: char*
• Booleans: bool (look into stdbool.h)
COMP 520 Winter 2019 – Assignment 2 Specifications Page 1/ 3
Variable Initialization
Variable initialization (i.e. the initial value specified in a declaration) must follow the assignment
compatibility rules described in the section below. If an initial value is not specified, it should be
automatically initialized in the generated code according to the following rules:
• Integers: 0
• Float: 0.0
• Strings: “”
• Booleans: false
• Read into a variable according to C scanf semantics. Use %d for integers, %f for floats, and
%s for strings and booleans (buffer size of 1024).
Note that booleans must be read in as either “true” or “false” (case-sensitive) and converted
to the appropriate true or false value. Anything else should produce a runtime error (i.e.
an error produced by your generated code).
• Print an expression according to C printf semantics for integers, floats, and strings. For
booleans, print “true” or “false”.
print(x * x);
• Assignment into a variable. Assignment compatibility is as follows:
int := int
float := float, int
string := string
boolean := boolean
Note that floats may not be assigned to ints.
• If statement, with zero or more else if and optional else branch. The conditions (<expression)
for all branches must be booleans
if (<expression) {
[else if (<expression) {
[else {
COMP 520 Winter 2019 – Assignment 2 Specifications Page 2/ 3
• While loop. The condition <expression must be a boolean
while (<expression) {
Literals in MiniLang have their corresponding types. i.e. an integer literal is of type int, etc.
Binary Operations
Given a binary expression <expr1 <op <expr2 where <op is one of +, -, *, /:
• int <op int is OK and results in type int
• float <op float is OK and results in type float
• int <op float (and vice-versa) is OK and results in type float
• string + string is OK and results in type string. The semantics of this operation are string
Given a binary expression <expr1 <op <expr2 where <op is one of &&, ||
• <expr1 and <expr2 must be of type bool
• The resulting expression has type bool
Given a binary comparison <expr1 <op <expr2 where <op is one of ==, !=:, <, , <=, =
• <expr1 and <expr2 can be of any type
• <expr1 and <expr2 must be of the same type
• The resulting expression has type bool
Unary Operations
Given a unary minus expression -<expression
• <expression must be either of type int or of type float
• The resulting expression has the same type as <expression
Given a unary not expression !<expression
• <expression must be of type bool
• The resulting expression has type bool
COMP 520 Winter 2019 – Assignment 2 Specifications Page 3/ 3