Shawn (Jan 30 2024 at 07:06): Shawn (Jan 30 2024 at 07:06):How come this doesn't work? It doesn't seem to infer that .firstName and .lastName need to be strings
main =
Stdout.line (greet { firstName: "Rocy", lastName: "Balboa" })
greet = "Hello $(.firstName) $(.lastName)!"
── TYPE MISMATCH in main.roc ───────────────────────────────────────────────────
This argument to this string interpolation has an unexpected type:
15│ greet = "Hello $(.firstName) $(.lastName)!"
^^^^^^^^^
This .lastName value is a:
{ lastName : a }b -> a
But this string interpolation needs its argument to be:
Str
────────────────────────────────────────────────────────────────────────────────
String interpolation is a syntax sugar for Str.concat so roc expects all passed arguments to be strings (see Str.concat type)
But .firstName and .lastName are getters of a record field
Also, roc has no currying so the function must be defined explicitly. So greet in your example is not a function but a string. As a result, you want smth like:
main =
Stdout.line (greet { firstName: "Rocy", lastName: "Balboa" })
greet = \user -> "Hello $(user.firstName) $(user.lastName)!"
Last updated: Jul 26 2025 at 12:14 UTC