add support for quoted atoms to writeq

src/prolog/io.rs

@@ -1,6 +1,7 @@
 use prolog::ast::*;
 use prolog::heap_print::*;
 use prolog::machine::*;
+use prolog::ordered_float::OrderedFloat;
 
 use termion::raw::IntoRawMode;
 use termion::input::TermRead;
@@ -24,17 +25,30 @@ impl fmt::Display for IndexPtr {
 
 impl fmt::Display for Constant {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fn print_atom(f: &mut fmt::Formatter, atom: &ClauseName) -> fmt::Result {
+            let non_quoted_token = |c| {
+                graphic_token_char!(c) || alpha_numeric_char!(c)
+            };
+
+            match atom.as_str() {
+                ";" | "!" => write!(f, "{}", atom.as_str()),
+                s => if s.chars().all(non_quoted_token) {
+                    write!(f, "{}", atom.as_str())
+                } else {
+                    write!(f, "{}", "'".to_owned() + atom.as_str() + "'")
+                }
+            }
+        }
+
         match self {
             &Constant::Atom(ref atom) =>
-                if atom.as_str().chars().any(|c| ".$'\" ".contains(c)) {
-                    write!(f, "'{}'", atom.as_str())
-                } else {
-                    write!(f, "{}", atom.as_str())
-                },
+                print_atom(f, atom),
             &Constant::Char(c) =>
                 write!(f, "'{}'", c as u8),
             &Constant::EmptyList =>
                 write!(f, "[]"),
+            &Constant::Number(Number::Float(ref fl)) if fl == &OrderedFloat(0f64) =>
+                write!(f, "0"),
             &Constant::Number(ref n) =>
                 write!(f, "{}", n),
             &Constant::String(ref s) =>