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LDC-E8702 — Parameter value type mismatch

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# LDC-E8702 — Parameter value type mismatch

## What it means

A parameter dataset declares one value type for all its rows, and every
row must carry a value of exactly that kind. A row with a different value
type — or with a currency where the declared kind takes none, a unit
where it takes a currency, or a currency that disagrees with the other
rows — breaks the promise that any row may answer for the parameter, so
the compiler stops at the row.

Align the row with the declared value type: same kind, same currency or
unit convention across all rows.

## Example

```run
{"argv": ["check", "$ROOT"], "files": {"law.toml": "[package]\nname = \"demo.diagnostics\"\nversion = \"0.1.0\"\nlanguage = \"0.2\"\nnamespace = \"urn:demo:diagnostics\"\n", "main.law": "language \"law.core\" version \"0.2\";\npackage demo.diagnostics version \"0.1.0\";\nnamespace \"urn:demo:diagnostics\";\n\nentity Person;\n", "mrp.lawparam.json": "{\"schemaVersion\": \"law.params/0.1\", \"kind\": \"parameter-dataset\", \"id\": \"urn:demo:diagnostics#mrp\", \"parameter\": \"urn:demo:diagnostics#MRP\", \"valueType\": {\"name\": \"urn:law:std#Money\"}, \"timeAxis\": \"legal_time\", \"granularity\": \"date\", \"coverage\": {\"start\": \"2025-01-01\", \"endExclusive\": null}, \"values\": [{\"id\": \"urn:demo:diagnostics#mrp#2025\", \"valid\": {\"start\": \"2025-01-01\", \"endExclusive\": \"2026-01-01\"}, \"value\": {\"kind\": \"value\", \"type\": {\"name\": \"urn:law:std#Decimal\"}, \"value\": \"3932\", \"currency\": \"KZT\"}, \"anchors\": [\"urn:demo:diagnostics#law#article-9\"]}, {\"id\": \"urn:demo:diagnostics#mrp#2026\", \"valid\": {\"start\": \"2026-01-01\", \"endExclusive\": null}, \"value\": {\"kind\": \"value\", \"type\": {\"name\": \"urn:law:std#Money\"}, \"value\": \"4325\", \"currency\": \"KZT\"}, \"anchors\": [\"urn:demo:diagnostics#law#article-9\"]}]}", "law.lock": "{\"lockVersion\": \"0.2\", \"resources\": [{\"capability\": \"compile_time\", \"contentHash\": \"sha256:9a030ae32e08f7c1aabc838b65c81a9429799935d3c952063088a9fd710b6f57\", \"id\": \"urn:demo:diagnostics#mrp\", \"kind\": \"parameter-dataset\", \"path\": \"mrp.lawparam.json\"}]}"}, "expect": "LDC-E8702"}
```

## Fix

```run
{"argv": ["check", "$ROOT"], "files": {"law.toml": "[package]\nname = \"demo.diagnostics\"\nversion = \"0.1.0\"\nlanguage = \"0.2\"\nnamespace = \"urn:demo:diagnostics\"\n", "main.law": "language \"law.core\" version \"0.2\";\npackage demo.diagnostics version \"0.1.0\";\nnamespace \"urn:demo:diagnostics\";\n\nentity Person;\n", "mrp.lawparam.json": "{\"schemaVersion\": \"law.params/0.1\", \"kind\": \"parameter-dataset\", \"id\": \"urn:demo:diagnostics#mrp\", \"parameter\": \"urn:demo:diagnostics#MRP\", \"valueType\": {\"name\": \"urn:law:std#Money\"}, \"timeAxis\": \"legal_time\", \"granularity\": \"date\", \"coverage\": {\"start\": \"2025-01-01\", \"endExclusive\": null}, \"values\": [{\"id\": \"urn:demo:diagnostics#mrp#2025\", \"valid\": {\"start\": \"2025-01-01\", \"endExclusive\": \"2026-01-01\"}, \"value\": {\"kind\": \"value\", \"type\": {\"name\": \"urn:law:std#Money\"}, \"value\": \"3932\", \"currency\": \"KZT\"}, \"anchors\": [\"urn:demo:diagnostics#law#article-9\"]}, {\"id\": \"urn:demo:diagnostics#mrp#2026\", \"valid\": {\"start\": \"2026-01-01\", \"endExclusive\": null}, \"value\": {\"kind\": \"value\", \"type\": {\"name\": \"urn:law:std#Money\"}, \"value\": \"4325\", \"currency\": \"KZT\"}, \"anchors\": [\"urn:demo:diagnostics#law#article-9\"]}]}", "law.lock": "{\"lockVersion\": \"0.2\", \"resources\": [{\"capability\": \"compile_time\", \"contentHash\": \"sha256:4e67c8dd00f9f81714dac9ebb458546f98ab9a868cda961b9f181d474bdcb33d\", \"id\": \"urn:demo:diagnostics#mrp\", \"kind\": \"parameter-dataset\", \"path\": \"mrp.lawparam.json\"}]}"}, "expect": null}
```

## Engine message

The parameter checker reports this in its own wording:

```text
LDC-E8702: value type does not equal dataset.valueType
```

## Related

- [LDC-E8701](/diagnostics/LDC-E8701/) — the neighbouring parameter refusal.