cd function

Signed-off-by: Ava Hahn <ava@sunnypup.io>

src/stl/posix.rs

@@ -15,18 +15,33 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-use crate::segment::{Ctr, Seg};
-use crate::sym::{SymTable, ValueType, Symbol, Args};
-use crate::eval::eval;
-use crate::run;
-use std::collections::VecDeque;
-use std::cell::RefCell;
-use std::rc::Rc;
-use std::fs::File;
-use std::process::{Command, Child, Stdio};
-use nix::unistd;
-use ctrlc;
-use std::fs::OpenOptions;
+use {
+    crate::{
+        segment::{Ctr, Seg},
+        sym::{
+            SymTable, ValueType,
+            Symbol, Args,
+        },
+        eval::eval,
+        run,
+    },
+
+    std::{
+        collections::VecDeque,
+        cell::RefCell,
+        rc::Rc,
+        fs::{File, OpenOptions},
+        path::Path,
+        process::{
+            Command, Child,
+            Stdio,
+        },
+        env::set_current_dir,
+    },
+
+    nix::unistd,
+    ctrlc,
+};
 
 pub struct ShellState {
     pub parent_pid: unistd::Pid,
@@ -54,7 +69,8 @@ pub fn args_from_ast(ast: &Seg, syms: &mut SymTable) -> Vec<String> {
                         _ => args.push(res_ctr.to_string()) == (),
                     }
                 } else {
-                    eprintln!("couldnt eval args!") != ()
+                    eprintln!("couldnt eval args: {}",
+                              eval_res.err().unwrap()) != ()
                 }
             },
             Ctr::Seg(ref form) => {
@@ -67,7 +83,8 @@ pub fn args_from_ast(ast: &Seg, syms: &mut SymTable) -> Vec<String> {
                         _ => args.push(res_ctr.to_string()) == (),
                     }
                 } else {
-                    eprintln!("couldnt eval args!") != ()
+                    eprintln!("couldnt eval args: {}",
+                              eval_res.err().unwrap()) != ()
                 }
             },
             Ctr::Lambda(_) => eprintln!("lambda passed as shell parameter") != (),
@@ -443,6 +460,21 @@ fn bg_callback(_ast: &Seg, _syms: &mut SymTable, _state: &mut ShellState) -> Res
     unimplemented!()
 }
 
+pub const CD_DOCSTRING: &str =
+    "Expects 1 argument (a string). Changes to a new directory";
+pub fn cd_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, String> {
+    if let Ctr::String(ref dir) = *ast.car {
+        let dirp = Path::new(dir);
+        if let Err(s) = set_current_dir(&dirp) {
+            Err(format!("{}", s))
+        } else {
+            Ok(Ctr::None)
+        }
+    } else {
+        Err(format!("impossible err: arg not a string"))
+    }
+}
+
 pub fn load_posix_shell(syms: &mut SymTable, shell_state: Rc<RefCell<ShellState>>) {
     let pid = unistd::getpid();
     let pgid_res = unistd::getpgid(Some(pid));