Gleam is cool. I wrote some services with it to see if I wanted to use it for more projects. It seemed like a good option because it would be easy to teach.

Things I like:

• fast build times (I only tested small apps though, under 2000 LOC)
• strong static types
• runs on the BEAM
• easy to learn
• pattern matching
• immutable + structural sharing
• currying (with parameter holes)

Things I don't like:

• no re-exports
• it's possible to have name collisions between packages; authors have a gentleman's agreement to always create a top-level module with the same name as the package
• some standard library APIs seem missing or immature (it's still pre-1.0)
• it can be hard to get good performance out of idiomatic code for specific tasks (see immutability)
• no format strings; best you can do is "Hello, " <> name. It starts to get cumbersome
• parsing/serialization is all quite manual boilerplate; there's nothing quite like serde
• no field/argument punning
• no method syntax; you just have to scan the docs to figure out what functions can be used with a given type
• you can't define the same variant name twice in the same module; I believe this is a limitation in how the types are translated to Erlang records
• you can't call functions in pattern matching if guards
• you can't have dependency cycles between modules in the same package
• hard to write FFI correctly; you lose all the comfort of types