Introduction

Who said Perl is old? Here is an example using Perl with Object Oriented Programming

The code implements a number calculator using a REST API and a CLI.

It uses Perl 6, OOP, Dancer for the web API, GetOpts long for the CLI and a few other things. This is part of a quick project to test some "new" functionalities in Perl.

Project Structure

The code is structured in 4 files.

• calc_cli.pl: the CLI driver
• calc_api.pl: the web api driver
• CalcCore.pm: the shared code or the main class of the app
• CalcResult.pm: return object, for both the CLI and Web API.

Requirements

You can use a perl package manager like "pm" or use the packet manager from your OS.

This is one way to install the requirements in Ubuntu:

sudo apt get install libdancer-perl libtemplate-perl libscalar-util-numeric-perl libdancer-plugin-rest-perl libjson-perl

Command line usage

To start the Dancer webserver simply call:

./calc_api.pl

Then you can visit some URLs, which will give you valid json responses:

http://0.0.0.0:3000/multiply/3/44

{
  result: "132",
  message: "multiplication result of 3 44 = 132 ",
  error: "0"
}

http://0.0.0.0:3000/factorial/3

{
result: "6",
message: "factorial 3! = 6 ",
error: "0"
}

http://0.0.0.0:3000/factorial/3sdf

{
result: "-1",
message: "Error. Cannot do a factorial of 3sdf because it is not a non-negative integer ",
error: "1"
}

http://0.0.0.0:3000/divide/3/0

{
result: "",
message: "Error. Not even us can divide by 0 (3 / 0) ",
error: "1"
}

http://0.0.0.0:3000/add/3/3

{
result: "6",
message: "add result of 3 3 = 6 ",
error: "0"
}

The field error indicates if an error occurred and the message field adds a human touch to its interface.

Command Line usage

To run calc_cli.pl just make sure it is executable chmod +x calc_api.pl

./calc_api.pl -h

Options: 

-h 
print help

-t 
 basic tests
 
-add [float] -add [float] ... 
 add several floats
 
-multiply [float] -multiply [float] ... 
 multiply several floats
 
-substract1 [float] -substract2 [float]
 substract1-substract2 floats
 
-divide1 [float] -divide2 [float]
 divide1/divide2 floats
 
-factorial [integer]
 factorial integer!

Try calc_api.pl -t to run some tests. Results are not checked with a testing library just to make this test a bit shorter but they would obviously be if it was done through a normal job.

The app is preventing some apps to receive incorrectly strings, and other invalid parameters (such as a float when expecting a natural number)

./calc_cli.pl -t

add result of 2 = 2
add result of 2 3 = 5
add result of 2 3 3 4 = 12
error: substraction of : we only can substract two numbers.
error: substraction of 2: we only can substract two numbers.
substraction result of 2 3 = -1
error: substraction of 2 3 3 4: we only can substract two numbers.
multiplication result of 2 3 3 4 = 72
division result 2 / 3 = 0.666666666666667
error: Not even us can divide by 0 (2 / 0)
error: Not even us can divide by 0 (2 / )
error: Cannot do a factorial of -2 because it is not a non-negative integer
factorial 5! = 120
error: Cannot do a factorial of 5.3 because it is not a non-negative integer
factorial 0! = 1
add result of saf-2 = 0

Since it is using GetOpts long some parameters allow a variable number of arguments:

./calc_cli.pl -a 3 -a 3 -add 5

add result of 3 3 5 = 11

./calc_cli.pl -f 3

 factorial 3! = 6

Give a try to test the rest of the options described in help.