Parsing Slack /remind command

3 min readJul 22, 2020

Have you ever wondered how Slack /remind commands works under the hood?

You just type

/remind @sibelius work tomorrow

and Slack knows that it should remind @sibelius to work tomorrow.

It feels Slack understanding natural language.

However, this is not a fancy machine learning algorithm, neither GPT3.

You can achieve the same behavior creating a simple parser in a few lines

Understanding Slack /remind command structure

The /remind command has 4 parts:

/remind: word that tells slack that we want to remind someone or a channel about something in the future
@someone or #channel: who or which channel we want to remind
what: what do we want to remind someone or some channel
when: when do we want the reminder to happen

Basic Grammar concepts

Grammar is a group of rules.

A rule can be a terminal or a non-terminal

A terminal rule does not expand anymore and does not use other rules example:

when -> (“today” | “tomorrow” | “next week”)

The rule above tells us that when can be today or tomorrow or next week .

A non-terminal rule is build of other rules, example:

someone_channel -> someone:? channel:?

In the rule above someone_channel can be something produced by someone rule or something produced by channel .

Building a Simple Grammar to parse it

main -> "/remind" _ someone_channel _ what _ when

Our main rule (non-terminal) will just describe the /remind command.

The remind commands need the /remind string, followed by a space(_ represents an obligatory space), followed by a someone_channel , then space , then what , then space then when .

Everything that is not inside quotes or _ needs to be defined by other rules.

Let's take a look at the definition of the rest of the rules:

Let's explain each of those.

someone_channel needs someone or channel , both are optional (?), you need to make sure the input has at least one of them.

someone is a "@" followed by a nickname, in this case, we are using Regex to match 1 or more letters

channel is a "#" followed by a channel name, that followed the same pattern as the nickname.

what is a regex matching, it can be improved to match numbers and more than one word

when for now only matches today tomorrow next week , feel free to improve it.

Give a Try

You can give a try to a working version of this grammar in this repository slack-reminder-grammar.

You can give a try right now from your terminal

npx slack-reminder-grammar "/remind #general party next week"

What's Next?

You can build your own simple languages to power your SaaS business or just for fun.

Ping me on twitter if you wanna talk https://twitter.com/sseraphini

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