Add support for positive integer ranges

Including support for variables and subexpressions as range bounds.

crates/nu-protocol/src/ast/expr.rs

@@ -1,4 +1,4 @@
-use super::{Call, Expression, Operator};
+use super::{Call, Expression, Operator, RangeOperator};
 use crate::{BlockId, Signature, Span, VarId};
 
 #[derive(Debug, Clone)]
@@ -6,6 +6,11 @@ pub enum Expr {
     Bool(bool),
     Int(i64),
     Float(f64),
+    Range(
+        Option<Box<Expression>>,
+        Option<Box<Expression>>,
+        RangeOperator,
+    ),
     Var(VarId),
     Call(Box<Call>),
     ExternalCall(Vec<u8>, Vec<Vec<u8>>),

crates/nu-protocol/src/ast/expression.rs

@@ -7,6 +7,7 @@ pub struct Expression {
     pub span: Span,
     pub ty: Type,
 }
+
 impl Expression {
     pub fn garbage(span: Span) -> Expression {
         Expression {
@@ -15,6 +16,7 @@ impl Expression {
             ty: Type::Unknown,
         }
     }
+
     pub fn precedence(&self) -> usize {
         match &self.expr {
             Expr::Operator(operator) => {

crates/nu-protocol/src/ast/operator.rs

@@ -1,3 +1,5 @@
+use crate::Span;
+
 use std::fmt::Display;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -46,3 +48,24 @@ impl Display for Operator {
         }
     }
 }
+
+#[derive(Debug, Copy, Clone, PartialEq)]
+pub enum RangeInclusion {
+    Inclusive,
+    RightExclusive,
+}
+
+#[derive(Debug, Copy, Clone)]
+pub struct RangeOperator {
+    pub inclusion: RangeInclusion,
+    pub span: Span,
+}
+
+impl Display for RangeOperator {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self.inclusion {
+            RangeInclusion::Inclusive => write!(f, ".."),
+            RangeInclusion::RightExclusive => write!(f, "..<"),
+        }
+    }
+}