The terraform fmt command is used to rewrite Terraform configuration files to a canonical format and style. This command applies a subset of the Terrra Terraform language style conventions, along with other minor adjustments for readability.

The Terraform language will automatically convert number and bool values to string values when needed, and vice-versa as long as the string contains a valid representation of a number or boolean value.
Example
* true converts to "true", and vice-versa
* false converts to "false", and vice-versa
* 15 converts to "15", and vice-versa
Where possible, Terraform automatically converts values from one type to another in order to produce the expected type. If this isn't possible, Terraform will produce a type mismatch error and you must update the configuration with a more suitable expression.
https://www.terraform.io/docs/configuration/expressions.html#type-conversion

Explanation
A terraform list is a sequence of values identified by consecutive whole numbers starting with zero.
https://www.terraform.io/docs/configuration/types.html#structural-types