LDC-E2121 — A wrong parameter count on a parametric type

What it means

Some type names take parameters, and each of them takes a fixed number: one element type for a list or an option, two for a map, and so on. The closed table of parametric names and their counts is part of the language, so a count that does not match the table cannot mean anything the compiler could keep. The compiler stops at the type expression and names the shape it expected.

The fix stays inside the type expression: add the missing parameter or drop the extra one until the count matches the table. A name outside the table takes no parameter at all and is refused under a different code.

Example

Arxo Law

language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

entity KZT;
relation r(x: Option<Integer, Text>) kind empirical;

Fix

Arxo Law

language "law.core" version "0.2";
package demo.diagnostics version "0.1.0";
namespace "urn:law:demo:diagnostics";

entity KZT;
relation r(x: Option<Integer>) kind empirical;

Engine message

The engine reports this in its own wording:

Output

example.law:6:15: error LDC-E2121: type `Option` takes 1 parameter(s) — the §35 table prints `Option<T>`, got 2 (errata E-0201). The list of parametric std names and each one's parameter count are closed by §35 and grow only via errata; on a std name OUTSIDE this list a parameter is rejected under its own code (errata E-0194). Before E-0201 an extra or missing parameter was lowered into the type node `args` and checked by nothing

Related

• Vocabulary — how names are declared and which positions take them.