refactor: improved error messages with descriptive type and operator information

src/evaluator/expression/call/mod.rs

@@ -23,7 +23,10 @@ impl Evaluator {
                 self.environment.pop();
                 Ok(block_call_evaluation)
             }
-            _ => anyhow::bail!("UncallableObject"),
+            object => anyhow::bail!(
+                "Cannot call an object of type {}, only functions are callable.",
+                object.type_name()
+            ),
         }
     }
 }

src/evaluator/expression/infix/mod.rs

@@ -13,15 +13,21 @@ impl Evaluator {
             match operator {
                 InfixOperator::Equals => Ok(Object::True),
                 InfixOperator::NotEquals => Ok(Object::False),
-                _ => anyhow::bail!("UnknownOperator"),
+                _ => anyhow::bail!(
+                    "Unknown operator, the {} infix operator is not supported for operands of type BOOLEAN.",
+                    operator
+                ),
             }
         }
 
         fn evaluate_opposite_boolean(operator: InfixOperator) -> anyhow::Result<Object> {
             match operator {
                 InfixOperator::Equals => Ok(Object::False),
                 InfixOperator::NotEquals => Ok(Object::True),
-                _ => anyhow::bail!("UnknownOperator"),
+                _ => anyhow::bail!(
+                    "Unknown operator, the {} infix operator is not supported for operands of type BOOLEAN.",
+                    operator
+                ),
             }
         }
 
@@ -57,17 +63,29 @@ impl Evaluator {
                         false => Ok(Object::False),
                     },
                 },
-                _ => anyhow::bail!("TypeMismatch"),
+                right_hand_object => anyhow::bail!(
+                    "Type mismatch, cannot apply the {} infix operator to operands of type INTEGER and {}.",
+                    operator,
+                    right_hand_object.type_name()
+                ),
             },
             Object::True => match self.evaluate_expression(right_hand)? {
                 Object::True => evaluate_same_boolean(operator),
                 Object::False => evaluate_opposite_boolean(operator),
-                _ => anyhow::bail!("TypeMismatch"),
+                right_hand_object => anyhow::bail!(
+                    "Type mismatch, cannot apply the {} infix operator to operands of type BOOLEAN and {}.",
+                    operator,
+                    right_hand_object.type_name()
+                ),
             },
             Object::False => match self.evaluate_expression(right_hand)? {
                 Object::False => evaluate_same_boolean(operator),
                 Object::True => evaluate_opposite_boolean(operator),
-                _ => anyhow::bail!("TypeMismatch"),
+                right_hand_object => anyhow::bail!(
+                    "Type mismatch, cannot apply the {} infix operator to operands of type BOOLEAN and {}.",
+                    operator,
+                    right_hand_object.type_name()
+                ),
             },
             Object::String { value: left_value } => match self.evaluate_expression(right_hand)? {
                 Object::String { value: right_value } => match operator {
@@ -86,11 +104,22 @@ impl Evaluator {
                             value: concatenated,
                         })
                     }
-                    _ => anyhow::bail!("UnknownOperator"),
+                    _ => anyhow::bail!(
+                        "Unknown operator, the {} infix operator is not supported for operands of type STRING.",
+                        operator
+                    ),
                 },
-                _ => anyhow::bail!("TypeMismatch"),
+                right_hand_object => anyhow::bail!(
+                    "Type mismatch, cannot apply the {} infix operator to operands of type STRING and {}.",
+                    operator,
+                    right_hand_object.type_name()
+                ),
             },
-            _ => anyhow::bail!("UnknownOperator"),
+            left_hand_object => anyhow::bail!(
+                "Unknown operator, the {} infix operator is not supported for operands of type {}.",
+                operator,
+                left_hand_object.type_name()
+            ),
         }
     }
 }

src/evaluator/expression/prefix/mod.rs

@@ -12,7 +12,10 @@ impl Evaluator {
         match object {
             Object::True => Ok(Object::False),
             Object::False => Ok(Object::True),
-            _ => anyhow::bail!("TypeMismatch"),
+            object => anyhow::bail!(
+                "Type mismatch, cannot apply the ! prefix operator to an operand of type {}.",
+                object.type_name()
+            ),
         }
     }
 
@@ -24,7 +27,10 @@ impl Evaluator {
 
         match object {
             Object::Integer { value } => Ok(Object::Integer { value: -value }),
-            _ => anyhow::bail!("TypeMismatch"),
+            object => anyhow::bail!(
+                "Type mismatch, cannot apply the - prefix operator to an operand of type {}.",
+                object.type_name()
+            ),
         }
     }
 }

src/evaluator/model/object/mod.rs

@@ -37,3 +37,16 @@ impl fmt::Display for Object {
         }
     }
 }
+
+impl Object {
+    pub(crate) fn type_name(&self) -> &'static str {
+        match self {
+            Object::Return { .. } => "RETURN",
+            Object::Integer { .. } => "INTEGER",
+            Object::String { .. } => "STRING",
+            Object::True | Object::False => "BOOLEAN",
+            Object::Null => "NULL",
+            Object::Function { .. } => "FUNCTION",
+        }
+    }
+}

src/evaluator/statement/let_statement/mod.rs

@@ -11,7 +11,10 @@ impl Evaluator {
         let expression = self.evaluate_expression(expression)?;
 
         if let Object::Return { value: _ } = expression {
-            anyhow::bail!("UnassignableObject");
+            anyhow::bail!(
+                "Cannot assign an object of type RETURN to the identifier {}.",
+                identifier
+            );
         }
 
         self.environment.set(identifier, expression);

src/syntax_analysis/expression/utilities/mod.rs

@@ -65,7 +65,9 @@ impl SyntaxAnalysis<'_> {
                         }
                     },
                     None => {
-                        anyhow::bail!("A {context} ended abruptly.");
+                        anyhow::bail!(
+                            "A {context} ended abruptly, expecting either a Comma or ClosingRoundBracket token."
+                        );
                     }
                 }
             }

src/syntax_analysis/model/syntax_tree_node/mod.rs

@@ -71,3 +71,20 @@ pub(crate) enum Expression {
         arguments: Vec<Expression>,
     },
 }
+
+impl std::fmt::Display for InfixOperator {
+    fn fmt(&self, formatter: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        let operator = match self {
+            InfixOperator::Plus => "+",
+            InfixOperator::Minus => "-",
+            InfixOperator::Multiply => "*",
+            InfixOperator::Divide => "/",
+            InfixOperator::Equals => "==",
+            InfixOperator::NotEquals => "!=",
+            InfixOperator::LesserThan => "<",
+            InfixOperator::GreaterThan => ">",
+        };
+
+        formatter.write_str(operator)
+    }
+}

src/tests/evaluation_error/type_mismatch_boolean_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_boolean_infix_expression__test_type_mismatch_boolean_infix_expression_case_1_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 31
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the == infix operator to operands of type BOOLEAN and INTEGER.",
 )

src/tests/evaluation_error/type_mismatch_boolean_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_boolean_infix_expression__test_type_mismatch_boolean_infix_expression_case_2_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 31
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the == infix operator to operands of type STRING and BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_boolean_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_boolean_infix_expression__test_type_mismatch_boolean_infix_expression_case_3_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 31
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the != infix operator to operands of type INTEGER and STRING.",
 )

src/tests/evaluation_error/type_mismatch_boolean_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_boolean_prefix_expression__test_type_mismatch_boolean_prefix_expression_case_1_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 26
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - prefix operator to an operand of type BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_boolean_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_boolean_prefix_expression__test_type_mismatch_boolean_prefix_expression_case_2_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 26
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - prefix operator to an operand of type BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_boolean_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_boolean_prefix_expression__test_type_mismatch_boolean_prefix_expression_case_3_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 26
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - prefix operator to an operand of type BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_boolean_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_boolean_prefix_expression__test_type_mismatch_boolean_prefix_expression_case_4_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 26
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - prefix operator to an operand of type BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_10_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - infix operator to operands of type STRING and INTEGER.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_11_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the + infix operator to operands of type STRING and INTEGER.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_12_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - infix operator to operands of type STRING and INTEGER.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_13_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the * infix operator to operands of type STRING and INTEGER.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_14_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the * infix operator to operands of type INTEGER and STRING.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_1_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the + infix operator to operands of type INTEGER and BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_2_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - infix operator to operands of type INTEGER and BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_3_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the * infix operator to operands of type BOOLEAN and INTEGER.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_4_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the / infix operator to operands of type INTEGER and BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_5_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the + infix operator to operands of type STRING and BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_6_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the - infix operator to operands of type BOOLEAN and STRING.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_7_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the * infix operator to operands of type BOOLEAN and STRING.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_8_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the / infix operator to operands of type STRING and BOOLEAN.",
 )

src/tests/evaluation_error/type_mismatch_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_infix_expression__test_type_mismatch_integer_infix_expression_case_9_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 48
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the + infix operator to operands of type INTEGER and STRING.",
 )

src/tests/evaluation_error/type_mismatch_integer_prefix_expression/snapshots/monkey_interpreter__tests__evaluation_error__type_mismatch_integer_prefix_expression__test_type_mismatch_integer_prefix_expression_case_1_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 23
 expression: error
 ---
 Err(
-    "TypeMismatch",
+    "Type mismatch, cannot apply the ! prefix operator to an operand of type INTEGER.",
 )

src/tests/evaluation_error/unknown_operator_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__unknown_operator_integer_infix_expression__test_unknown_operator_integer_infix_expression_case_1_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 32
 expression: error
 ---
 Err(
-    "UnknownOperator",
+    "Unknown operator, the + infix operator is not supported for operands of type BOOLEAN.",
 )

src/tests/evaluation_error/unknown_operator_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__unknown_operator_integer_infix_expression__test_unknown_operator_integer_infix_expression_case_2_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 32
 expression: error
 ---
 Err(
-    "UnknownOperator",
+    "Unknown operator, the - infix operator is not supported for operands of type BOOLEAN.",
 )

src/tests/evaluation_error/unknown_operator_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__unknown_operator_integer_infix_expression__test_unknown_operator_integer_infix_expression_case_3_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 32
 expression: error
 ---
 Err(
-    "UnknownOperator",
+    "Unknown operator, the * infix operator is not supported for operands of type BOOLEAN.",
 )

src/tests/evaluation_error/unknown_operator_integer_infix_expression/snapshots/monkey_interpreter__tests__evaluation_error__unknown_operator_integer_infix_expression__test_unknown_operator_integer_infix_expression_case_4_evaluation_error.snap

@@ -4,5 +4,5 @@ assertion_line: 32
 expression: error
 ---
 Err(
-    "UnknownOperator",
+    "Unknown operator, the / infix operator is not supported for operands of type BOOLEAN.",
 )