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kojix2
kojix2

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Embedding the Crystal Compiler in Your Program

#crystal

Introduction

The Crystal compiler can be used as a library.
This document explains how to set it up and use it.

Creating the Project

First, create a new Crystal project.

crystal init app duck_egg cd duck_egg
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Editing shard.yml

Edit the shard.yml file as follows.
In this example, we add markd and reply to the dependencies section.

name: duck_egg version: 0.1.0 targets: 🥚: main: src/duck_egg.cr dependencies: markd: github: icyleaf/markd reply: github: I3oris/reply
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Creating duck_egg.cr

Create src/duck_egg.cr and add the following code.

require "compiler/requires" BIRDS = [ { "🐔", "cluck!" }, { "🐓", "cock-a-doodle-doo" }, { "🦃", "gobble" }, { "🦆", "quack" }, { "🦉", "hoot" }, { "🦜", "squawk" }, { "🕊", "coo" }, { "🦢", "honk" }, { "🦩", "brrrrt" }, { "🐧", "honk honk" }, { "🦤", "boop" }, { "🦕", "Bwooooon!!" }, { "🦖", "Raaaaawr!!" } ] bird, sound = BIRDS.sample compiler = Crystal::Compiler.new source = Crystal::Compiler::Source.new(bird, %Q(puts "#{bird} < #{sound}")) compiler.compile source, bird
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In this program, the Crystal compiler is embedded in the target 🥚.
When 🥚 is executed, a random bird is selected.
The embedded compiler generates a binary that displays the bird and its sound.

Building and Running

First, build the program.

shards build
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Next, check the CRYSTAL_PATH environment variable to find the location of the Crystal standard library.

crystal env
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The Crystal compiler requires the standard library even for very simple code such as puts 0.
Therefore, CRYSTAL_PATH must be set to include the path to the standard library.

export CRYSTAL_PATH=lib:/usr/local/bin/../share/crystal/src
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Run the program:

bin/🥚
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Example output:

🦖
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Run the generated binary:

./🦖
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Output:

🦖 < Raaaaawr!!
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Summary

By using the Crystal compiler as a library, you can generate and compile code dynamically. This technique can be applied in many interesting ways.

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