Compile errors¶

situ fails closed: everything outside the compiled dialect, the seam, or the composition envelope is a CompileError raised at compile time, so problems surface as visible errors while you develop. In dev the error appears on your framework's debug page (Litestar's or Flask's); in the lint loop, tests and situ check catch it. The compiler carries 111 distinct rejection sites; the inline messages are maintained as part of the API. This page catalogs the ones you'll actually meet, with their fixes.

The seam¶

The dialect¶

An operand whose type is not known¶

cannot compile this comparison: the type of `id` is not known here, and situ will not decide it
with a runtime coercion. Give it a type — annotate the handler parameter (`def go(id: int)`),
declare the signal's element type (`Local[list[Row]]`), or declare the row's record with
`data-row="<Record>"` — and the comparison compiles to the lowering its types imply.

Situ compiles == / != / in from the operand types: str == str is a plain compare, int == int normalizes through Number(), list == list is structural. When it cannot establish a type, there is no rule to apply, so it refuses.

It used to guess. A runtime helper coerced both sides through Number() and compared, which reported 3 == [3] as true and made a non-numeric value (a status string, a filter id) never compare equal. That helper is gone as of 0.4.0.

Most often the operand is a handler parameter missing an annotation, and situ already infers those from their call sites: go(t.id) with t.id: int types go's parameter for you. You see this error when inference could not settle it: the call sites disagree, one of them passes something untypable, or the handler is never called.

The three fixes, in the order you will usually reach for them:

# 1. annotate the parameter; always works, and says what you meant
def go(id: int):
    if id == selected:
        ...

# 2. declare the signal's element type, so a row read has one
rows: Local[list[Issue]] = []      # not a bare Local[list]

# 3. declare the row's record, so `t.field` is decoded to its real type
#    <li :each="t in rows" data-row="Issue">
class Issue(TypedDict):
    id: int
    title: str

Templates¶

Composition¶

declui¶