You can see that the sum package is specified as a local dependency in the math package's package.json. This is OK, because pnpm will convert the local dependency into a semver dependency on publish.

pnpm configuration

Some of the configs are changed in order to make pnpm work well with the monorepo. There is an .npmrc file in the root of the monorepo with three config values. Lets see what each of them are doing.

link-local = true

This is the most important change for a monorepo. The link-local config makes pnpm synlink local dependencies and convert them to semver depencies before publish. More detailes about this option at: usage in monorepos

store-path = ~/.store

This makes pnpm use a global store. Packages in monorepos usually have a big set of common dependencies. A common store will keep all the dependencies in one place, giving a huge boost to the installation time. More detailes about shared stores here.

save-exact = false

Specifying a save-exact config in the root of your monorepo is not obligatory but a good thing. It will guarantee consistency upon how pnpm publish will convert the local dependencies into semver dependencies. Will it use exact or not exact versions.