CSE340 Type Checking

CSE340 Spring 2021 Project 3: Type Checking
Due: Tuesday, Arpil 1, 2021 by 11:59 pm MST
The goal of this project is to give you experience in Hindley-Milner type checking.
We begin by introducing the grammar of our language which is based on the previous project with
additional constructs. Then we will discuss the semantics of our language and type checking rules.
Finally we will go over a few examples and formalize the expected output.

1. Lexical Specification
   Here is the list of tokens that your lexical analyzer should recognize (the new tokens are listed first):
   INT = "int"
   REAL = "real"
   BOOL = "bool"
   TRUE = "true"
   FALSE = "false"
   IF = "if"
   WHILE = "while"
   SWITCH = "switch"
   CASE = "case"
   NOT = "!"
   PLUS = "+"
   MINUS = "-"
   MULT = "*"
   DIV = "/"
   GREATER = ">"
   LESS = "<"
   GTEQ = ">="
   LTEQ = "<="
   NOTEQUAL = "<>"
   LPAREN = "("
   RPAREN = ")"
   NUM = (pdigit digit*) + 0
   REALNUM = NUM "." digit digit*
   PUBLIC = "public"
   PRIVATE = "private"
   EQUAL = "="
   COLON = ":"
   COMMA = ","
   SEMICOLON = ";"
   LBRACE = "{"
   RBRACE = "}"
   ID = letter (letter + digit)*
2. Grammar
   Here is the grammar for our input language:
   program -> global_vars body
   global_vars -> ε
   global_vars -> var_decl_list
   var_decl_list -> var_decl
   var_decl_list -> var_decl var_decl_list
   var_decl -> var_list COLON type_name SEMICOLON
   var_list -> ID
   var_list -> ID COMMA var_list
   type_name -> INT
   type_name -> REAL
   type_name -> BOOL
   body -> LBRACE stmt_list RBRACE
   stmt_list -> stmt
   stmt_list -> stmt stmt_list
   stmt -> assignment_stmt
   stmt -> if_stmt
   stmt -> while_stmt
   stmt -> switch_stmt
   assignment_stmt -> ID EQUAL expression SEMICOLON
   expression -> primary
   expression -> binary_operator expression expression
   expression -> unary_operator expression
   unary_operator -> NOT
   binary_operator -> PLUS | MINUS | MULT | DIV
   binary_operator -> GREATER | LESS | GTEQ | LTEQ | EQUAL | NOTEQUAL
   primary -> ID
   primary -> NUM
   primary -> REALNUM
   primary -> TRUE
   primary -> FALSE
   if_stmt -> IF LPAREN expression RPAREN body
   while_stmt -> WHILE LPAREN expression RPAREN body
   switch_stmt -> SWITCH LPAREN expression RPAREN LBRACE case_list RBRACE
   case_list -> case
   case_list -> case case_list
   case -> CASE NUM COLON body
3. Language Semantics
   3.1. Types
   The language has three built-in types: int , real and bool .
   3.2. Variables
   Programmers can declare variables either explicitly or implicitly.
   Explicit variables are declared in an var_list of a var_decl .
   A variable is declared implicitly if it is not declared explicitly but it appears in the
   program body.
   Example
   Consider the following program written in our language:
   x: int;
   y: bool;
   {
   y = x;
   z = 10;
   w = * z 5;
   }
   This program has four variables declared: x , y , z , and w , with x and y explicitly declared and z
   and w implicitly declared.
   3.3. Type System
   Our language uses structural equivalence for checking type equivalence. Implicit types will
   be inferred from the usage (in a simplified form of Hindley-Milner type inference).
   Here are all the type rules/constraints that your type checker will enforce (constraints are
   labeled for reference):
   C1: The left hand side of an assignment should have the same type as its right hand side
   C2: The operands of a binary operator ( GTEQ
   , LTEQ , EQUAL and NOTEQUAL
   PLUS , MINUS , MULT , DIV , GREATER , LESS , )
   should have the same type (it can be any type)
   C3: The operand of a unary operator ( NOT ) should be of type bool
   C4: Condition of if and while statements should be of type bool
   C5: The expression that follows the switch keyword in switch_stmt should be of type
   int
   The type of expression binary_operator op1 op2 is the same as the type of op1 and
   op2 if operator is PLUS , MINUS , MULT or DIV . Note that op1 and op2 must have
   the same type due to C2
   The type of expression binary_operator op1 op2 is bool if operator is GREATER ,
   LESS , GTEQ , LTEQ , EQUAL or NOTEQUAL
   The type of expression unary_operator op is bool
   NUM constants are of type int
   REALNUM constants are of type real
   true and false values are of type bool
4. Output
   There are two scenarios:
   There is a type error in the input program
   There are no type errors in the input program
   4.1. Type Error
   If any of the type constraints (listed in the Type System section above) is violated in the
   input program, then the output of your program should be:
   TYPE MISMATCH
   Where is replaced with the line number that the violation occurs and
   should be replaced with the label of the violated type constraint (possible values
   are C1 through C5). Note that you can assume that anywhere a violation can occur it will be on a
   single line.
   4.2. No Type Error
   If there are no type errors in the input program, then you should output type information for all
   variables in the input program in the order they appear in the program. There are two cases:
   If the type of the variable is determined to be one of the builtin types, then output one line in
   the following format:
   : #
   where should be replaced by the variable name and should be
   replaced by the type of the variable.
   If the type of the variable could not be determined to be one of the builtin types, then you
   need to list all variables that have the same type as the target variable and mark all of
   them as printed (so as to not print a separate entry for those later). You should output one
   line in the following format:
   : ? #
   where is a comma-separated list of variables that have the same type
   in the order they appear in the program.
5. Examples
   Given the following:
   a, b: int;
   {
   a = < b 2;
   }
   The output will be the following:
   TYPE MISMATCH 3 C1
   This is because the type of < b 2 is bool , but a is of type int which is a violation of C1.
   Given the following:
   a, b: int;
   {
   a = + b 2.5;
   }
   The output will be the following:
   TYPE MISMATCH 3 C2
   This is because the type of b is int and the type of 2.5 is real which means in the
   expression + b 2.5 , C2 is violated
   Given the following:
   a, b: int;
   {
   a = b;
   }
   The output will be the following:
   a: int #
   b: int #
   Given the following:
   {
   a = b;
   }
   The output will be the following:
   a, b: ? #
   Note that b is not listed separately because it is marked as printed when listed with a on the first
   line of the output.
   Given the following:
   {
   a = + 1 b;
   }
   The output will be the following:
   a: int #
   b: int #
   Given the following:
   {
   if (<= a b)
   {
   a = 2.4;
   }
   }
   The output will be the following:
   a: real #
   b: real #
   Given the following:
   {
   if (a)
   {
   b = * 2 b;
   }
   }
   The output will be the following:
   a: bool #
   b: int #
   Given the following:
   a, b: int;
   c: int;
   {
   x = + a * b c;
   y = ! true;
   }
   The output will be the following:
   a: int #
   b: int #
   c: int #
   x: int #
   y: bool #
   Given the following:
   {
   x = + a * b c;
   y = ! < a x;
   z = w;
   }
   The output will be the following:
   x, a, b, c: ? #
   y: bool #
   z, w: ? #
   Note that z and w are not listed with x .
6. Requirements
   You should use C/C++, no other programming languages are allowed.
   You should submit your code on the course submission website, no other submission
   forms will be accepted.
   Also submit the output file obtained from the server
7. Evaluation
   The submissions are evaluated based on the automated test cases on the submission website.
   Your grade will be proportional to the number of test cases passing. If your code does not
   compile on the submission website, you will not receive any points.
   Here is the breakdown of points for tests in different categories:
   Test cases with assignment statements (no if , while or switch ): 50 points
   Test cases with assignment, if and while statements (no switch ): 30 points
   Test cases with all types of statements: 20 points