Make variable assignment convert streams to full values

TODO.md

@@ -14,12 +14,15 @@
 - [x] parsing tables
 - [x] Block params
 - [x] Ranges
+- [ ] Iteration (`each`) over tables
+- [ ] ctrl-c support
 - [ ] Column path
 - [ ] ...rest without calling it rest
 - [ ] operator overflow
 - [ ] finish operator type-checking
 - [ ] Source
 - [ ] Autoenv
+- [ ] Externals
 - [ ] let [first, rest] = [1, 2, 3]
   
 ## Maybe: 

crates/nu-protocol/src/engine/evaluation_context.rs

@@ -22,6 +22,29 @@ impl EvaluationContext {
     }
 
     pub fn add_var(&self, var_id: VarId, value: Value) {
+        // We need to make values concreate before we assign them to variables, as stream values
+        // will drain and remain drained.
+        //
+        // TODO: find a good home for this
+        // TODO: add ctrl-c support
+
+        let value = match value {
+            Value::RowStream {
+                headers,
+                stream,
+                span,
+            } => Value::Table {
+                headers,
+                val: stream.collect(),
+                span,
+            },
+            Value::ValueStream { stream, span } => Value::List {
+                val: stream.collect(),
+                span,
+            },
+            x => x,
+        };
+
         self.stack.add_var(var_id, value);
     }
 

src/tests.rs

@@ -228,3 +228,11 @@ fn range_iteration2() -> TestResult {
 fn simple_value_iteration() -> TestResult {
     run_test("4 | each { $it + 10 }", "14")
 }
+
+#[test]
+fn concrete_variable_assignment() -> TestResult {
+    run_test(
+        "let x = (1..100 | each { |y| $y + 100 }); $x | length; $x | length",
+        "100",
+    )
+}