S0027: type mismatch

Generated from rellum-diagnostics/src/db.rs.

Explanation

Every binding, function parameter, match arm, and feedback state has one concrete type. For feedback state, the initial value establishes the state type for all future ticks; every clause must produce that same type so the state slot has a stable layout.

Common causes

• a feedback clause returns a different type than the initial value
• passing an argument whose type does not match the function parameter
• returning different types from match arms
• using a lambda where a non-function type is expected

Canonical fixes

• make the expression produce the expected type

Before:

count: Int ~ feedback(
    on press => "one",
    0
)

After:

count: Int ~ feedback(
    on press => 1,
    0
)

• change the annotation or initial value when the new type is intended

Before:

count: Int ~ feedback(
    on press => "one",
    0
)

After:

count: String ~ feedback(
    on press => "one",
    "zero"
)

• convert explicitly with a helper such as to_string

Before:

message: String = count

After:

message: String = to_string(count)

Code example

count: Int ~ feedback(
    on press => "one",
    0
)

Links

• RellC diagnostic overview