[shimon]

This is the promise of type inference. Languages like Elm that do a good job inferring types are able to play out potentially invalid implications of how your code uses values without requiring you to separately specify all your types in great detail. You'll spend some time just addressing edge cases as "safe to ignore" but it's a lot lower than explicit typing while delivering many of its benefits.

[skybrian]

Type inference usually makes it harder for a compiler to provide good error messages though. Elm has gone the extra mile on this.

[tlrobinson]

Flow actually does type inference as well.