add ps and early help

crates/nu-engine/src/call_ext.rs

@@ -0,0 +1,47 @@
+use nu_protocol::{ast::Call, engine::EvaluationContext, ShellError};
+
+use crate::{eval_expression, FromValue};
+
+pub trait CallExt {
+    fn get_flag<T: FromValue>(
+        &self,
+        context: &EvaluationContext,
+        name: &str,
+    ) -> Result<Option<T>, ShellError>;
+
+    fn rest<T: FromValue>(
+        &self,
+        context: &EvaluationContext,
+        starting_pos: usize,
+    ) -> Result<Vec<T>, ShellError>;
+}
+
+impl CallExt for Call {
+    fn get_flag<T: FromValue>(
+        &self,
+        context: &EvaluationContext,
+        name: &str,
+    ) -> Result<Option<T>, ShellError> {
+        if let Some(expr) = self.get_flag_expr(name) {
+            let result = eval_expression(context, &expr)?;
+            FromValue::from_value(&result).map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+
+    fn rest<T: FromValue>(
+        &self,
+        context: &EvaluationContext,
+        starting_pos: usize,
+    ) -> Result<Vec<T>, ShellError> {
+        let mut output = vec![];
+
+        for expr in self.positional.iter().skip(starting_pos) {
+            let result = eval_expression(context, expr)?;
+            output.push(FromValue::from_value(&result)?);
+        }
+
+        Ok(output)
+    }
+}