Platypus

Platypus is a is truely minimal language. In its entirety, it consists of:

• variable assignment
• binary operations
• if conditional
• if-else conditional
• while loops

Grammar

Platypus uses PLY to write the grammar.

program: function

function: FUNCTION ( var_list ) { summary stmt_list RETURN ( var_list ) }

summary: SUMMARY

var_list: VAR var_list

var_list:

stmt_list: stmt stmt_list

stmt_list:

value: VAR

value: NUMBER

condn: value comparison_op value

condn: value

stmt: VAR = value

stmt: VAR = value comparison_op value

stmt: VAR = value arithmatic_op value

stmt: WHILE ( condn ) { stmt_list }

stmt: IF ( condn ) { stmt_list }

stmt: IF ( condn ) { stmt_list } ELSE { stmt_list }

comparison_op: < | > | <= | >= | == | !=

arithmatic_op: + | * | / | - | %

Installation

$ pip install platypus

Usage

The following program computes the sum of the first N numbers and returns it. Save this file as say sum_till_N.platypus

function(N) {
    
# this function calculates the sum of first n numbers #
    i = 0
    sum = 0
    c = 1
    while (c) {
        sum = sum + i
        i = i + 1
        if(i >= N) {
            c = 0
        }
    }
    
    return(sum)
}

Now, run

$ platypus -i sum_till_N.platypus

You would be presented with a shell. To execute the function, simply enter the argument(s) in the shell. In case of sum_till_N(), the only argument is N.

platypus $ 12

The result would look like

[66]

Another example. The following function returns the greatest number among the arguments a1, a2 & a3. Save this file as greater.platypus

function (a1 a2 a3) {
# this function calculates the greatest amongst the three entered numbers #
    
    ans = a1
    if (a2 > a1) {
        ans = a2
        if(a3 > a2) {
            ans = a3
        }
    }
    else {
        if(a3 > a1) {
        ans = a3
        }
    }
    return (ans)
}

Again run platypus and pass in the arguments in the shell.

platypus $ 1 1 10

The result would look like

[10]

Platypus can also be used to return multiple values. Save the following program as fibo_sum.platypus

function (a1 a2 N) {
# returns the Nth fibonacci number & the sum of first N fibonacci numbers#

    if (N == 1) {
        fibo = a1
        sum = a1
    }
    else {
        if (N == 2) {
            fibo = a2
            sum = a1 + a2
        }
        else {
        i = 3
        sum = a1 + a2
        anow = a2
        aprev = a1
            while (i <= N) {
                temp = anow
                anow = anow + aprev
                aprev = temp
                i = i + 1
                sum = sum + anow
            }
            fibo = anow
        }
    }

return (fibo sum)
}

Running this program with a1 = 1, a1 = 2 & N = 8

platypus $ 1 1 8

This should output

[21, 54]