To my surprise when you search for gleam read file in google, they are not much helpful information in the first page and no code example.
There are a post in Erlang Forums where the author of Gleam language pointed to a module that no longer exists in gleam_erlang pacakge, and a abandoned pacakge call gleam_file, and a couple pacakges like simplifile.
It turns out that Gleam has excellent FFI that if you are running it on BEAM (which is the default option unless you compile Gleam to javascript), for a simple case you just need to import the function from erlang, in just two lines of code.
@external(erlang, "file", "read_file")
fn read_file(file_path: String) -> Result(String, Nil)
and you can use it as a normal function to read the file content into a string.
pub fn read_file_as_string(path: String) {
use content <- result.try(
read_file(path)
|> result.map_error(fn(_) { "Failed to read file: " <> path }),
)
content
}