merge with master

src/main.rs

@@ -1,6 +1,7 @@
 extern crate crossterm;
 #[macro_use]
 extern crate downcast;
+extern crate git_version;
 extern crate indexmap;
 #[macro_use]
 extern crate lazy_static;
@@ -11,6 +12,7 @@ extern crate prolog_parser;
 #[macro_use]
 extern crate ref_thread_local;
 
+use git_version::git_version;
 use nix::sys::signal;
 
 mod prolog;
@@ -19,6 +21,7 @@ use crate::prolog::machine::*;
 use crate::prolog::machine::streams::*;
 use crate::prolog::read::*;
 
+use std::env;
 use std::sync::atomic::Ordering;
 
 extern fn handle_sigint(signal: libc::c_int) {
@@ -32,6 +35,11 @@ fn main() {
     let handler = signal::SigHandler::Handler(handle_sigint);
     unsafe { signal::signal(signal::Signal::SIGINT, handler) }.unwrap();
 
+    if env::args().skip(1).any(|a| a == "-v" || a == "--version") {
+        println!("{:}", git_version!());
+        return;
+    }
+
     let mut wam = Machine::new(readline::input_stream(), Stream::stdout());
     wam.run_top_level();
 }

src/prolog/examples/least_time.pl

@@ -4,7 +4,7 @@
  *
  *  find_min_time/2 solves a problem sometimes posed in the first round
  *  of Google interviews: given a time of day in 24 H format, what is the
- *  lexographically least permutation of the time that is itself a
+ *  lexicographically least permutation of the time that is itself a
  *  valid time in 24 H format?
  *
  *  Full generality is achieved using the reif library.