Formula language reference

Formulas are string expressions evaluated at transaction build time. They appear in output/input amount_sat, validation expr, hook set values, and witness expr.

Operators

Operator	Description
`+` `-` `*` `/`	Integer arithmetic (division truncates)
`==` `!=` `<` `<=` `>` `>=`	Comparison (returns boolean)
`&&` `\|\|` `!`	Boolean logic
`(` `)`	Grouping

References

Syntax	Description
`compile_params.NAME`	Compile parameter by name
`params.NAME`	Action parameter by name
`args.NAME`	Action argument by name
`input_id.amount_sat`	Satoshi amount of a resolved input
`input_id.asset`	Asset ID of a resolved input (hex string)
`input_id.present`	Boolean — whether an optional input was found
`output_id.amount_sat`	Satoshi amount of a constructed output (post-construction)
`fees`	Estimated transaction fee (used in change formulas)

Functions

Function	Signature	Description
`pow(base, exp)`	(u64, u64) → u64	Integer exponentiation
`index_of(id)`	(input or output id) → u32	Transaction index of a named input/output
`concat(a, b, …)`	(bytes…) → bytes	Byte concatenation (`OP_RETURN` `data` only)

See Spec.md §9 for the authoritative grammar.