Compiler

Simple compiler carried out during the Compilers subject in the URV Computer Science degree.

Pre-requisites

• gcc
• flex
• bison

Functioning

Build

$ make

Run

$ ./compiler INPUT_FILE OUTPUT_FILE

You can also put your input files in the input folder and run:

$ make run

Clean

$ make clean

Documentation

This compiler generates a simple three address code. It works with Integers and Floats and all the iterative and conditional sentences specified below.

Modes

The compiler has two functioning modes:

• calc on: compiler set in the calculator mode.
• calc off: compiler set in the program mode.

It has to be indicated in the first line of the input file, so the syntax of the file must be:

calc on_or_off
statement list

Allowed Types

• INTEGER x := 10
• REAL x := 1.500
• STRING x := "hola"
• BOOLEAN x := true | false

Arithmetic Operations

• + Add
• - Substract
• * Multiplication
• / Division
• mod Module
• ** Power
• sqrt Square Root

Relational Operators

• > Bigger than
• >= Bigger or equal than
• < Less than
• <= Less or equal than
• = Equal than
• <> Different from

Boolean Operators

• not
• and
• or

Statements

Statements can be such arithmetic expressions:

They are formed by int, float or string literals, identifiers, arithmetic expressions between parenthesis, and the string concatenation operator (+) and the other arithmetic operators (+ , - , * , / , mod, ** , sqrt ) applied over other arithmetic expressions. The sqrt function is not suported by the compiler mode.

i * (x + i) - i / 4.0
17 + (3 * 1.0)
s + (s + i) + x

boolean expressions:

They are formed by boolean literals and identifiers, boolean operators applied over other boolean expressions and relational expressions applied over arithmetic expressions. Boolean expressions are only suported in conditional and iterative statements in the compiler mode.

true
b or not b
z > 3
(i > 0 and i <= 10) or false

assignations (id := expression):

In an assignation, the identifier type is the same as the expression result type.

z := i * (x + i) - i / 4.0
s := "Hola"
p := "hola" + 5.456
s := 3 --(4)
b := z > 3 or not (i > 0 and i <= 10) or false

• If same type arithmetic expression are operated, the result has the same type.
• If integers and reals are arithmeticaly operated, the result has real type.
• If a string is concatenated (+) with a number, the result has string type.
• All the identifiers that apear in an expression, need to be initialized.

conditional statements:

If statement syntax:

if boolean expression then
    statement list
fi

If else statement syntax:

if boolean expression then
    statement list
else
    statement list
fi

Elsif statement syntax:

if boolean expression then
    statement list
elsif boolean expression then
    statement list
elsif boolean expression then
    statement list
...
else
    statement list
fi

Switch statement syntax:

switch arithmetic expression begin
    case LITERAL :
        statement list
    case LITERAL :
        statement list
    ...
    default :
        statement list
end

or iterative statements:

While statement syntax:

while boolean expression do
    statement list
done

Repeat Until statement syntax:

repeat
    statement list
until boolean expression

For statement syntax:

for id in range do
    statement list
done

Do While statement syntax:

do
    statement list
while boolean expression

The range is defined as: arithmetic expression .. arithmetic expression

The identifier used in the for statement has to be an uninitialized variable.

Error treatment

Conditional and iterative statements are not allowed in the calculator mode, so it will be treated as an error.

The following errors have also been considered:

• It is checked that the expressions type is correct before doing any arithmetic operation.
• If an identifier is used in an expression, is checked if it has been initialized.
• When an assignation is carried out, if it was initialized before, it is checked if the identifier and the expression have the same type.

If any of this errors happens, an error message ( with error kind and the line ) will be send and the program will finish.

Examples

There are some example files in the input folder.

Calculator mode example file:

calc on

// assignations
x := 1.5
i := 5
z := i * (x + i) - i / 4.0
b := z > 3 or not (i > 0 and i <= 10) or false
s := "Hello"
// expressions
x
i + i * 2
s + " " + (s + i) + x
b or not b

Program mode example file:

calc off

// nested sentences
total := 0.0
i := 1
while total < 1000.0 do
    if (i = 1) then
        total := total * 2
    else
        total := total - 1
    fi
    i := -i
done
total

// Fibonacci numbers
n := 50
x := 1
x
y := 1
y
for index in 3..n do
    fib := x + y
    x := y
    y := fib
    fib
done

calc off

// nested sentences
total := 0.0
i := 1
while total < 1000.0 do
    if (i = 1) then
        total := total * 2
    else
        total := total - 1
    fi
    i := -i
    if total > 666.6 or total = 500.0 then
        i := 1
    fi
done
total

Author

• Cristòfol Daudén Esmel - toful