# LibTmux.Query.Expr

- **Package:** libtmux-haskell
- **Language:** Haskell
- **Kind:** data type
- **Source:** https://github.com/libtmux/libtmux-haskell/blob/663e212622a02aa74a9bdc8ff71e2b45fcb1d4d5/internal/LibTmux/Internal/Query.hs#L100
- **Page:** https://libtmux.org/en/haskell/latest/reference/libtmux-query-t-expr/

```haskell
data Expr row
```

A pure predicate description for one row type. Field and relationship
 tokens retain their identity; arbitrary application functions stay outside
 this portable representation. Nominal roles prevent cross-row coercion.