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Running a Prolog Script

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Introduction

Prolog is intended primarily as a declarative programming language: the program logic is expressed in terms of relations, represented as facts and rules. A computation is initiated by running a query over these relations. Prolog is well-suited for specific tasks that benefit from rule-based logical queries such as searching databases, voice control systems, and filling templates.

TD;LR

A quick guide on how to run a hello world script on Bacalhau

Prerequisites

To get started, you need to install the Bacalhau client, see more information here

Running Locally​

To get started, install swipl

%%bash
sudo add-apt-repository ppa:swi-prolog/stable
sudo apt-get update
sudo apt-get install swi-prolog

Create a file called helloworld.pl. The following script prints ‘Hello World’ to the stdout

%%writefile helloworld.pl
hello_world :- write('Hello World'), nl,
halt.

Running the script to print out the output

%%bash
swipl -q -s helloworld.pl -g hello_world

After the script has run successfully locally we can now run it on Bacalhau.

Before running it on Bacalhau we need to upload it to IPFS.

Using the IPFS cli

!wget https://dist.ipfs.io/go-ipfs/v0.4.2/go-ipfs_v0.4.2_linux-amd64.tar.gz
!tar xvfz go-ipfs_v0.4.2_linux-amd64.tar.gz
!mv go-ipfs/ipfs /usr/local/bin/ipfs
!ipfs init
!ipfs cat /ipfs/QmYwAPJzv5CZsnA625s3Xf2nemtYgPpHdWEz79ojWnPbdG/readme
!ipfs config Addresses.Gateway /ip4/127.0.0.1/tcp/8082
!ipfs config Addresses.API /ip4/127.0.0.1/tcp/5002
!nohup ipfs daemon > startup.log &

Run the command below to check if our script has been uploaded. This command outputs the CID.

!ipfs add helloworld.pl

Copy the CID of the file which in this case is QmYq9ipYf3vsj7iLv5C67BXZcpLHxZbvFAJbtj7aKN5qii

Since the data uploaded To IPFS isn’t pinned, we will need to do that manually. Check this information on how to pin your data We recommend using NFT.Storage.

Running a Bacalhau Job

To submit a job, run the following Bacalhau command:

%%bash --out job_id
bacalhau docker run \
-i ipfs://QmYq9ipYf3vsj7iLv5C67BXZcpLHxZbvFAJbtj7aKN5qii:/helloworld.pl \
--wait \
--id-only \
swipl \
-- swipl -q -s helloworld.pl -g hello_world

Structure of the Command

-i: ipfs://< CID >:/< name-of-the-script >: we will mount the script to the container using the -v flag

Swipl: flag

-q: running in quiet mode

-s: load file as a script in this case we want to run the script helloworld.pl

-g: is the name of the function you want to execute in this case its hello_world

When a job is submitted, Bacalhau prints out the related job_id. We store that in an environment variable so that we can reuse it later on.

Checking the State of your Jobs

  • Job status: You can check the status of the job using bacalhau list.
%%bash
bacalhau list --id-filter ${JOB_ID} --wide

When it says Published or Completed, that means the job is done, and we can get the results.

  • Job information: You can find out more information about your job by using bacalhau describe.
%%bash
bacalhau describe ${JOB_ID}
  • Job download: You can download your job results directly by using bacalhau get. Alternatively, you can choose to create a directory to store your results. In the command below, we created a directory and downloaded our job output to be stored in that directory.
%%bash
rm -rf results && mkdir -p results
bacalhau get $JOB_ID --output-dir results

Viewing your Job Output

To view the file, run the following command:

%%bash
cat results/stdout