Parsing Slack /remind command

Photo by Jason Leung on Unsplash

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

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

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 .

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"

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