check molds

A mold is a type expressed as a normalizing function. rune check runs the mold checker over a program without executing it, reporting type mismatches it can catch statically.

All commands run from rs/.

a passing check

echo '6 * 7' > prog.rune
cargo run --bin rune -- check prog.rune

ok

a failing check

Bind a text literal to a numeric mold and the checker rejects it:

printf 'let x: @ud = "hi"\nx' > bad.rune
cargo run --bin rune -- check bad.rune

mold error: text literal bound to `@ud`, expected a text mold (@t)

check exits non-zero when it finds errors, so it composes in scripts and CI.

what is checked today

The checker validates literal-to-mold compatibility at typed binding sites — for example a text literal requires a text mold (@t), and a cell cannot be bound to @ud. The base molds (@ud @da @t @flag @p) and the strata algebra molds are recognised. See model.md for the full mold system.