README.md

MathLang

A calculator language

Introduction

MathLang is a stack based language that uses Polish style notation for its mathematical expressions. Polish notation is also sometimes referred to as prefix notation, meaning that operations are written before the operands. For example: add 1 2 does the 1 + 2 operation.

Syntax

Here is a table of all the syntax keywords and their meaning:

keyword
int	Declares a variable of type int.
float	Declares a variable of type float.
asg	Assigns a value to a variable of the appropriate type.
{ and }	Curly braces are markers for the beginning and end of either the main block, or an exec block as part of the if or while statement.
add	Returns sum of two values.
sub	Returns difference of two values.
mul	Returns product of two values.
div	Returns quotient of division of 2 values.
not	Returns the logical not of a value.
and	Returns the logical and of 2 values.
or	Returns the logical or of 2 values.
lt	Returns comparison result of "less then".
gt	Returns comparison result of "greater then".
eq	Returns the numerical boolean value of an equality. In case of floats checks with precision of 0.001.
print	prints a value to the console.
if	A conditional statement. Is composed of: if a boolean value or expression { a code block } else { alternative codeblock }
while	A loop statement. Is composed of: while a boolean value or expression { a code block }

Grammar

Structure

The structure of a program has 2 main parts:

• The preamble -- where variables are declared:

int a
float b

• And right after the main block between braces:

int a
float b
{
  asg a 44
  asg b 0.01
  print mul a b
}

Here print takes one argument, that being the return value of mul a b.

New lines and padding for inside exec blocks are not mandatory as MathLang keeps track of each operation and the number of its operands in the parser. So this is the same as above:

int a
float b
{ asg a 44 asg b 0.01 print mul a b }

NOTE exec blocks (including the main block) are nothing more than a list of expressions/statements separated at least by a newline or space that are executed consecutively.

Types

Besides number of operands, the MathLang's parser keeps track of one more thing: the types returned by each operations. Because type checking is performed at the parser level, a program with a as integer will refuse to even run in the following case:

asg a mul add a 4 div sub a 0.5

Printing the following error:

Parser Error: attempting to assign `a` of type int a return value of type float on line ...
...

For reference, here are the types returned by MathLang's operations:

• add, sub and mul: when both operands are an integer -- returns an integer, otherwise -- a float;
• div: always returns a float;
• not, and, or, eq, lt, gt: return an integer being either 0 or 1;
• asg and print: return nothing (they are not operations in the true sense of the word)

NOTE all returned values must be consumed. Meaning that operations like add 2 1 by their own are invalid. They must either be an argument to another operation, a value to be printed or assigned or an argument to the if or while statement.

Boolean values

In MathLang logical operations and the if and while statements treat numerical values as boolean:

• 0 and 0.0 are interpreted as false;
• any other int or float is interpreted as true.

Writing your first program

Let us implement a Fibonacci sequence generator step by step

1. First, we define our variables:

int n1 n2 i next

2. We need our building blocks: a 0 and a 1. As MathLang has values initialised with 0, we only need to:

asg n2 1

3. Next, we print our first two numbers:

print n1
print n2

4. And begin generating our Fibonacci up to 25 more numbers:

  while lt i 26 {
    asg next add n1 n2
    print next
    asg n1 n2
    asg n2 next
    asg i add i 1
  }

This while loop is executed as long as lt i 26, in other words as long as i is less that 26. Inside, the loop assigns to the variable next the sum of n1 and n2 and prints it. Then, it reconsiders the last two numbers of the sequence by assigning n2 to n1 and next to n2. Finally, i is incremented.

Here is the complete code:

int n1 n2 i next
{
  asg n2 1
  print n1
  print n2
  while lt i 26 {
    asg next add n1 n2
    print next
    asg n1 n2
    asg n2 next
    asg i add i 1
  }
}

For reference, the same code in C:

#include <stdio.h>

int main() {
    int n1 = 0, n2 = 1, i = 0, next;

    printf("%d\n", n1);
    printf("%d\n", n2);

    while (i < 26) {
        next = n1 + n2;
        printf("%d\n", next);
        n1 = n2;
        n2 = next;
        i++;
    }

    return 0;
}