Chapter 27 : Preprocessor

Instead of writing the LIGO code in a single file, it is possible to split the code into different files or include some external code into our file. The pre-processor is responsible for handling code inclusion. While working with multiple files we may encounter a problem of cyclic inclusion. To prevent such situation some pre-processor commands are available.

  • #if
  • #define
  • #include

⚠️ Notice all pre-processor command names start with a #.

Include

Pre-processor command #include permits code inclusion. It allows to merge some code into your file. Command #include requires a path to a ligo file.

#include "tzip-12/fa2_interface.mligo"

Define

Pre-processor command #define allows to introduce tags.

#define FA2_NFT_TOKEN

Such tags can be used with a conditionnal command.

Conditionnal

Pre-processor commands #if, #else and #endif allows to consider / ignore some part of the file depending on tags. Tags are defined with the #define command.

#if !FA2_NFT_TOKEN

#define FA2_NFT_TOKEN
#include "tzip-12/fa2_interface.mligo"

let substr_special (s: string) : string =
  String.sub 0n 4n s

#else
#include "test/fa2_int.mligo"

let substr_special (s: string) : string =
  String.sub 0n 3n s

#endif

⚠️ Notice that the conditionnal #if can be used to customize your includes.

⚠️ Notice that this pattern prevents variable or type redefinition in case of cyclic inclusion.

#if !X#define X

Your mission

We are implementing a smart contract with a modular approach.

As you can see in our exercise, when the WITH*EXTRA tag is defined then the code in extra.mligo file is included. The module _extra* defines the tag EXTRA and implements a function doSomethingExtra.

We want you to make the code responsive to the tag EXTRA.

1- Modify the function doSomethingInventory in the inventory contract inventory so as to execute doSomethingExtra on the given parameter if the EXTRA tag is defined. Otherwise execute removeFirst on the given parameter.