Cleanup recite(), custom errors, fixed forking

First off, moved the giant match statements out of recite(), and into
macros in src/recite/ps.rs. There still needs to be two, since any verse
using the 'couplet' meter will need to redirect its STDOUT. Now the
recite() function returns a Result<(), Mishap>, which can be invoked
when calling the incant_ functions.

Custom errors were added in the form of 'Mishap''s. They are intended to
be returned from the incant_ functions, in the event that something goes
wrong with the Command::spawn() or Child::wait(). They each take a
String, which should be the verb or stanza that was entered by the user.

The incant_ functions separate the functionality of each type of meter
from the recite() function. They return a Result<i32, Mishap>, where
i32 is the exit code of the program that ran, and Mishap is a possible
error.

Before, the shell was cheating at forking a process to the background.
It would actually spawn a thread to wait for that process to finish.
Now, the program simply registers a handler for SIGCHLD, and uses libc's
waitpid() function to reap the child process, and print some output to
the user, indicating that it's finished.

1 files changed, 16 insertions, 4 deletions

diff --git a/src/main.rs b/src/main.rs
index 986e006..44f2726 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,5 @@
 mod recite;
+use libc::{waitpid, WNOHANG};
 use recite::path::prefresh;
 use recite::Poem;
 use std::io::{self, Write};
@@ -53,11 +54,12 @@ fn repl(path: &Vec<&Path>, prompt: &str) {
         // Parse a poem
         let poem = Poem::read(poetry);
         match poem {
-            Some(poem) => {
-                poem.recite(path, &mut bins);
-            }
+            Some(poem) => match poem.recite(path, &mut bins) {
+                Ok(_) => {}
+                Err(e) => eprintln!("dwvsh: {}", e),
+            },
             None => {}
-        }
+        };
     }
 }
 
@@ -87,6 +89,16 @@ fn main() {
             io::stdout().flush().unwrap();
         })
         .unwrap();
+
+        signal_hook::low_level::register(signal_hook::consts::SIGCHLD, move || {
+            let mut status: i32 = -1;
+            let pid: i32 = waitpid(-1, &mut status, WNOHANG);
+            if pid != -1 {
+                print!("[&]  + done  {}", pid);
+                io::stdout().flush().unwrap();
+            }
+        })
+        .unwrap();
     };
 
     // Begin evaluating commands