This MR finishes up all remaining Pre V1 goals

* add a posix exit() builtin
* improve separation of concerns regarding standard library structure

src/stl/posix.rs

@@ -31,7 +31,7 @@ use {
         run,
     },
     libc::{
-        sigaddset, sigemptyset, sigprocmask,
+        sigaddset, sigemptyset, sigprocmask, exit,
         SIGINT, SIGCHLD, SIGTTOU, SIGTTIN, SIGQUIT, SIGTSTP,
         SIG_BLOCK, SIG_UNBLOCK
     },
@@ -633,6 +633,19 @@ fn q_callback(_ast: &Seg, _syms: &SymTable, state: &mut ShellState) -> Result<Ct
     Ok(Ctr::Integer(state.last_exit_code.into()))
 }
 
+const EXIT_DOCSTRING: &str = "Takes on integer input. calls libc exit() with given argument.";
+fn exit_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, Traceback> {
+    let mut ret = -1;
+    if let Ctr::Integer(i) = *ast.car {
+        ret = i;
+    } else {
+        eprintln!("WARNING: input was not an integer. Exiting -1.")
+    }
+    unsafe {
+        exit(ret as i32);
+    }
+}
+
 const BG_DOCSTRING: &str = "Calls a binary off disk with given arguments.
 Arguments may be of any type except lambda. If a symbol is not defined it will be passed as a string.
 first argument (command name) will be found on path (or an error returned).
@@ -681,7 +694,7 @@ fn bg_callback(ast: &Seg, syms: &mut SymTable, state: &mut ShellState) -> Result
     }
 }
 
-pub const FG_DOCSTRING: &str = "takes one argument (an integer).
+const FG_DOCSTRING: &str = "takes one argument (an integer).
 Integer is presumed to be a PID of a running background job.
 If PID corresponds with a background job, fg will try to foreground it.
 If PID is not a current running background job, fg will return an error.
@@ -689,7 +702,7 @@ If PID is not a current running background job, fg will return an error.
 Examples:
   (bg vim) (fg 13871)
 ";
-pub fn fg_callback(
+fn fg_callback(
     ast: &Seg,
     _syms: &mut SymTable,
     shell_state: &mut ShellState
@@ -709,9 +722,9 @@ pub fn fg_callback(
     }
 }
 
-pub const CD_DOCSTRING: &str =
+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, Traceback> {
+fn cd_callback(ast: &Seg, _syms: &mut SymTable) -> Result<Ctr, Traceback> {
     if let Ctr::String(ref dir) = *ast.car {
         let dirp = Path::new(dir);
         if let Err(s) = set_current_dir(&dirp) {
@@ -913,4 +926,28 @@ pub fn load_posix_shell(syms: &mut SymTable, shell_state: Rc<RefCell<ShellState>
             ..Default::default()
         },
     );
+
+    syms.insert(
+        String::from("exit"),
+        Symbol {
+            name: String::from("exit"),
+            args: Args::Strict(vec![Type::Integer]),
+            conditional_branches: false,
+            docs: String::from(EXIT_DOCSTRING),
+            value: ValueType::Internal(Rc::new(exit_callback)),
+            ..Default::default()
+        },
+    );
+
+    syms.insert(
+        "cd".to_string(),
+        Symbol {
+            name: String::from("cd"),
+            args: Args::Strict(vec![Type::String]),
+            conditional_branches: false,
+            docs: CD_DOCSTRING.to_string(),
+            value: ValueType::Internal(Rc::new(cd_callback)),
+            ..Default::default()
+        },
+    );
 }