LilyPond Contributor's Guide: 10.15.2 Conversion

### 10.15.2 Conversion

### General definitions

#### bool to_boolean (SCM b)

Return `true` if b is `SCM_BOOL_T`, else return `false`.

This should be used instead of `scm_is_true` and `scm_is_false` for properties since empty lists are sometimes used to unset them.

#### [C type] ly_scm2[C type] (SCM s)

Behave the same as scm_to_[C type] would do if it existed.

#### [C type] robust_scm2[C type] (SCM s, [C type] d)

Behave the same as scm_to_[C type] would do if it existed. Return d if type verification fails.

#### LilyPond — Contributor’s Guide v2.22.2 (stable-branch).