LDC-E2108 — Operands of incompatible kinds

For LLMs5 sections

What it means

Arithmetic and comparison work on matching kinds: adding a date to money, or ordering values that have no order, is rejected where it stands. The language performs no silent conversions between kinds — each operand must already be what the operation expects.

Rewriting the expression so both sides share a kind, or picking the operation that fits the kinds at hand, fixes it. The message names the two kinds found, which points straight at the side to change.

Example

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

relation out(x: Text, a: Money) kind institutional;
relation m(x: Text, a: Money) kind empirical;
relation d(x: Text, t: Date) kind empirical;
rule R strict { for x: Text; for a: Money; for t: Date; when m(x, a) and d(x, t); then out(x, (t + a)); }

Fix

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

relation out(x: Text, a: Money) kind institutional;
relation m(x: Text, a: Money) kind empirical;
relation d(x: Text, t: Date) kind empirical;
rule R strict { for x: Text; for a: Money; for b: Money; when m(x, a) and m(x, b); then out(x, (a + b)); }

Engine message

The engine reports this in its own wording:

example.law:8:96: error LDC-E2108: «+»: incompatible kinds Date and Money — §58 requires matching kinds for addition and subtraction; the §49 scalar rule applies ONLY to multiplication (§48: no implicit conversions)

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