Make expr displayable

src/expr.rs

@@ -1,3 +1,5 @@
+use std::fmt;
+use self::Expr::*;
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum Expr {
@@ -21,6 +23,52 @@ pub enum Expr {
     Error(Problem),
 }
 
+impl fmt::Display for Expr {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            // PRIMITIVES
+            Int(num) => write!(f, "{} : Int", *num),
+            Frac(numerator, denominator) => {
+                if *denominator == 10 {
+                    write!(f, "{} : Frac", (*numerator as f64 / 10.0))
+                } else {
+                    write!(f, "{}/{} : Frac", numerator, denominator)
+                }
+            },
+            Str(string) => {
+                let escaped_str =
+                    (*string)
+                        .replace("\\", "\\\\")
+                        .replace("\"", "\\\"")
+                        .replace("\t", "\\t")
+                        .replace("\n", "\\n")
+                        .replace("\r", "\\r");
+
+                write!(f, "\"{}\" : String", escaped_str)
+            },
+            Char(ch) => write!(f, "'{}' : Char", *ch),
+            Bool(true) => write!(f, "True : Bool"),
+            Bool(false) => write!(f, "False : Bool"),
+            Closure(args, _) => write!(f, "<{}-argument function>", args.len()),
+
+            // ERRORS
+            Error(Problem::UnrecognizedVarName(name)) => write!(f, "NAMING ERROR: Unrecognized var name `{}`", name),
+            Error(Problem::TypeMismatch(info)) => write!(f, "TYPE ERROR: {}", info),
+            Error(Problem::ReassignedVarName(name)) => write!(f, "REASSIGNED CONSTANT: {}", name),
+            Error(Problem::WrongArity(expected_arity, provided_arity)) => {
+                if provided_arity > expected_arity {
+                  write!(f, "TOO MANY ARGUMENTS: needed {} arguments, but got {}", expected_arity, provided_arity)
+                } else {
+                  write!(f, "MISSING ARGUMENTS: needed {} arguments, but got {}", expected_arity, provided_arity)
+                }
+            }
+
+            // UNFORMATTED
+            _ => write!(f, "<partially evaluated expression>")
+        }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq)]
 pub enum Problem {
     UnrecognizedVarName(String),
@@ -29,7 +77,6 @@ pub enum Problem {
     WrongArity(u32 /* Expected */, u32 /* Provided */),
 }
 
-
 #[derive(Clone, Debug, PartialEq)]
 pub enum Pattern {
     Identifier(String),