1 files changed, 72 insertions, 0 deletions
diff --git a/src/syntax/span.rs b/src/syntax/span.rs
new file mode 100644
index 00000000..aa494224
--- /dev/null
+++ b/src/syntax/span.rs
@@ -0,0 +1,72 @@
+//! Spans map elements to the part of source code they originate from.
+
+use std::fmt::{self, Display, Formatter};
+
+/// Annotates a value with the part of the source code it corresponds to.
+#[derive(Copy, Clone, Eq, PartialEq)]
+pub struct Spanned<T> {
+    pub val: T,
+    pub span: Span,
+}
+
+impl<T> Spanned<T> {
+    pub fn new(val: T, span: Span) -> Spanned<T> {
+        Spanned { val, span }
+    }
+
+    pub fn value(self) -> T {
+        self.val
+    }
+
+    pub fn span_map<F, U>(self, f: F) -> Spanned<U> where F: FnOnce(T) -> U {
+        Spanned::new(f(self.val), self.span)
+    }
+}
+
+impl<T> Display for Spanned<T> where T: std::fmt::Debug {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "({:?}:{})", self.val, self.span)
+    }
+}
+
+debug_display!(Spanned; T where T: std::fmt::Debug);
+
+/// Describes a slice of source code.
+#[derive(Copy, Clone, Eq, PartialEq)]
+pub struct Span {
+    pub start: usize,
+    pub end: usize,
+}
+
+impl Span {
+    pub fn new(start: usize, end: usize) -> Span {
+        Span { start, end }
+    }
+
+    pub fn merge(a: Span, b: Span) -> Span {
+        Span {
+            start: a.start.min(b.start),
+            end: a.end.max(b.end),
+        }
+    }
+
+    pub fn at(index: usize) -> Span {
+        Span { start: index, end: index + 1 }
+    }
+
+    pub fn pair(&self) -> (usize, usize) {
+        (self.start, self.end)
+    }
+
+    pub fn expand(&mut self, other: Span) {
+        *self = Span::merge(*self, other)
+    }
+}
+
+impl Display for Span {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        write!(f, "[{}, {}]", self.start, self.end)
+    }
+}
+
+debug_display!(Span);