diff options
Diffstat (limited to 'dhall_syntax/src/core.rs')
| -rw-r--r-- | dhall_syntax/src/core.rs | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/dhall_syntax/src/core.rs b/dhall_syntax/src/core.rs index c8a2425..389f037 100644 --- a/dhall_syntax/src/core.rs +++ b/dhall_syntax/src/core.rs @@ -60,7 +60,7 @@ pub enum Const { /// The `Int` field is a DeBruijn index. /// See dhall-lang/standard/semantics.md for details #[derive(Debug, Clone, PartialEq, Eq)] -pub struct Var<Label>(pub Label, pub usize); +pub struct Var<VarLabel>(pub VarLabel, pub usize); // Definition order must match precedence order for // pretty-printing to work correctly @@ -529,6 +529,19 @@ impl<'a> From<&'a Label> for Var<Label> { } } +/// Trait for things that capture a label used for variables. +/// Allows normalization to be generic in whether to alpha-normalize or not. +pub trait VarLabel: std::fmt::Display + Clone { + /// Is `self` the default variable (i.e. "_") ? + fn is_underscore_var(&self) -> bool; +} + +impl VarLabel for Label { + fn is_underscore_var(&self) -> bool { + &String::from(self) == "_" + } +} + /// `shift` is used by both normalization and type-checking to avoid variable /// capture by shifting variable indices /// See https://github.com/dhall-lang/dhall-lang/blob/master/standard/semantics.md#shift |