feat: display more information when an invalid expression construct i…

…s encountered (related to #10)

src/bridge/expr.rs

@@ -32,8 +32,8 @@ pub enum Expr {
 
 #[derive(Error, Debug, Clone)]
 pub enum EvalError {
-    #[error("encountered a terminal that cannot be evaluated")]
-    InvalidTerminal,
+    #[error("encountered a terminal that cannot be evaluated: {terminal}")]
+    InvalidTerminal{ terminal: String },
 }
 
 impl Expr {
@@ -102,7 +102,7 @@ impl Expr {
                 ) =>
             unsafe { ((**a).get_tristate_value() != (**b).get_tristate_value()).into() },
             Expr::Terminal(Terminal::Symbol(s)) => unsafe { (**s).get_tristate_value() },
-            Expr::Terminal(_) => return Err(EvalError::InvalidTerminal),
+            Expr::Terminal(t) => return Err(EvalError::InvalidTerminal{ terminal: format!("{:?}", t) }),
         })
     }
 

src/bridge/satisfier.rs

@@ -20,8 +20,8 @@ pub enum SolveError {
     Unsatisfiable,
     #[error("complex negated expressions are unsupported")]
     ComplexNot,
-    #[error("expression contains unsupported constructs")]
-    UnsupportedConstituents,
+    #[error("expression contains at least one unsupported construct: {description}")]
+    UnsupportedConstituents { description: String },
     #[error("expression contains an ambiguous comparison")]
     AmbiguousComparison,
     #[error("encountered an invalid symbol")]
@@ -219,7 +219,7 @@ impl Solver for SimpleSolver {
     fn satisfy(&self, bridge: &Bridge, expr: &Expr, desired_value: Tristate) -> Result<Assignments, SolveError> {
         // If the expression already evaluates to at least the desired value,
         // we don't have to change any variables
-        if expr.eval().map_err(|_| SolveError::UnsupportedConstituents)? >= desired_value {
+        if expr.eval().map_err(|e| SolveError::UnsupportedConstituents{ description: e.to_string() })? >= desired_value {
             return Ok(HashMap::new());
         }
 
@@ -262,7 +262,7 @@ impl Solver for SimpleSolver {
                     }
                 }
                 Expr::Terminal(Terminal::Symbol(s)) => self.satisfy_eq(&bridge.wrap_symbol(*s), Tristate::No)?,
-                Expr::Terminal(_) => return Err(SolveError::UnsupportedConstituents),
+                Expr::Terminal(k) => return Err(SolveError::UnsupportedConstituents{ description: format!("{:?}", k) }),
                 _ => return Err(SolveError::ComplexNot),
             },
             Expr::Terminal(Terminal::Eq(a, b)) => {
@@ -298,7 +298,7 @@ impl Solver for SimpleSolver {
                 };
                 self.satisfy_neq(&s, Tristate::No, desired_value)?
             }
-            Expr::Terminal(_) => return Err(SolveError::UnsupportedConstituents),
+            Expr::Terminal(k) => return Err(SolveError::UnsupportedConstituents{ description: format!("{:?}", k)}),
         })
     }
 }