Issue #514: Use cases for f[T](), a type named in brackets at a call (NK1233 asks for them)

Open and answer this issue on GitHub.

note · opened 2026-10-07 · updated 2026-10-26 · 0 comments

What this issue is for

Nikaia allows a call to name its type arguments in brackets: parse[Config](text). Every such call draws the warning NK1233, which links here.

Please leave a comment with:

• the call you wrote;
• why the type could not come from an argument (f(x)), or from the type passed where the parameter list holds one (schema(User), ADR-330 D1);
• what you would have written instead, if anything.

Why it is allowed, with a warning

This came up in the decision round on describing a type without a value (ADR-330).

• Two forms were weighed. schema(User) was chosen for describing a type: the type sits where the parameter list holds it. f[T]() had been rejected in ADR-323 §3 as “a new form for the whole language, for one use”.
• Hints that it may be needed:
  • a function whose result type is the only place T appears;
  • meta::column.
• Why a warning: the owner chose to allow it and collect the real use cases. NK1233 exists for that purpose.

Known costs:

• f[x] reads like an index; only the declaration of f tells the two apart.
• There are two ways to name a type at a call.

What happens with the answers

• The use cases decide one of three outcomes:
  • the warning goes, and f[T]() stays;
  • f[T]() is removed in favour of schema(T);
  • f[T]() is limited to the cases that need it.
• The status stays note until enough cases are in. The decision itself is an issue of its own, labelled decision.

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