better errors and interaction and lex parse

Author: alexhallam

CHANGELOG.md

@@ -1,5 +1,55 @@
 # Changelog
 
+## [0.2.3] - 2025-09-05
+
+### ✨ Added
+
+- **Enhanced Error Messages**: Added colored, user-friendly error reporting with contextual information
+  - Pretty-printed syntax errors show original formula, successful lexemes (green), and failed lexemes (red)
+  - Clear "Expected Token:" labels with clean token names
+  - Contextual display of parsing progress with colored highlighting using `owo-colors`
+- **Improved Parser Error Context**: Parse errors now include the exact position and context where parsing failed
+
+### 🔧 Improved
+
+- **Error Message Quality**: Cleaned up error messages to show "Function or ColumnName" instead of "Function token or ColumnName"
+- **Code Style**: Eliminated clippy warnings throughout the codebase
+  - Removed unnecessary `to_string()` calls in format strings
+  - Converted instance methods to static methods where appropriate
+  - Removed unnecessary return statements
+  - Fixed redundant pattern matching in examples
+
+### 🐛 Fixed
+
+- **Error Display**: Fixed duplicate and malformed error message formatting
+- **Documentation**: Removed duplicate doc comments and improved consistency
+
+### 📚 Documentation
+
+- **Error Handling**: Updated parser documentation to reflect new pretty error functionality
+- **Examples**: Added comprehensive error testing examples demonstrating colored output
+
+### 🧹 Code Quality
+
+- **Dead Code**: Eliminated all dead code warnings in main library
+- **Clippy Compliance**: Achieved zero clippy warnings for main library code
+- **Performance**: Optimized error formatting to avoid unnecessary string allocations
+
+### 🔄 Internal Changes
+
+- **Error Processing**: Streamlined error handling pipeline to preserve original `ParseError::Unexpected` for better formatting
+- **String Processing**: Improved error message generation to be more efficient and readable
+
+#### Example Output Format:
+```
+Syntax error- Unexpected Token
+Formula: y ~ x +
+Show: y ~ x + <eoi>
+Expected Token: Function or ColumnName
+```
+
+These changes maintain backward compatibility while significantly improving the developer experience when working with formula parsing errors.
+
 ## [0.2.2] - 2025-09-05
 
 added `lex_formula` for users to inspect raw lexer output

Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 description = "High-performance modern Wilkinson's formula parsing for statistical models. Parses R-style formulas into structured JSON metadata supporting linear models, mixed effects, and complex statistical specifications."
 name = "fiasto"
-version = "0.2.2"
+version = "0.2.3"
 edition = "2021"
 authors = ["Alex Hallam <alexhallam6.28@gmail.com>"]
 license = "MIT"

examples/test_pretty.rs

@@ -2,7 +2,7 @@ use fiasto::parse_formula;
 
 fn main() {
     // Test different error scenarios
-    let test_cases = vec![
+    let test_cases = [
         "y ~ x +",           // trailing plus
         "y ~ + x",           // leading plus  
         "~ x",               // missing response
@@ -13,7 +13,7 @@ fn main() {
     for (i, formula) in test_cases.iter().enumerate() {
         println!("\n=== Test case {} ===", i + 1);
         println!("Formula: {}", formula);
-        if let Err(_) = parse_formula(formula) {
+        if parse_formula(formula).is_err() {
             // Error is already printed by parse_formula via eprintln!
         }
     }

src/internal/meta_builder.rs

@@ -324,8 +324,8 @@ impl MetaBuilder {
         right: &crate::internal::ast::Term,
     ) {
         // Extract variable names from the interaction terms
-        let left_name = self.extract_variable_name(left);
-        let right_name = self.extract_variable_name(right);
+        let left_name = Self::extract_variable_name(left);
+        let right_name = Self::extract_variable_name(right);
 
         if let (Some(left_var), Some(right_var)) = (left_name, right_name) {
             // Ensure both variables exist
@@ -366,7 +366,7 @@ impl MetaBuilder {
     }
 
     /// Extracts variable name from a term
-    fn extract_variable_name(&self, term: &crate::internal::ast::Term) -> Option<String> {
+    fn extract_variable_name(term: &crate::internal::ast::Term) -> Option<String> {
         match term {
             crate::internal::ast::Term::Column(name) => Some(name.clone()),
             crate::internal::ast::Term::Function { name: _name, args } => {
@@ -381,7 +381,7 @@ impl MetaBuilder {
                 right: _right,
             } => {
                 // For nested interactions, we'll use the left side for now
-                self.extract_variable_name(left)
+                Self::extract_variable_name(left)
             }
             crate::internal::ast::Term::RandomEffect(_) => None,
         }

src/internal/parse_arg.rs

@@ -1,7 +1,5 @@
 use crate::internal::{ast::Argument, errors::ParseError, lexer::Token};
 
-/// Parses a single argument within a function call.
-
 /// Parses a single argument within a function call.
 ///
 /// This function handles individual arguments that can appear in function calls.

src/internal/parse_random_effect.rs

@@ -225,9 +225,9 @@ fn parse_correlation_type<'a>(
                     Some(id_slice.to_string()),
                 ))
             } else {
-                return Err(ParseError::Syntax(
+                Err(ParseError::Syntax(
                     "expected second '|' after correlation ID".into(),
-                ));
+                ))
             }
         } else {
             Ok((CorrelationType::Correlated, None))

src/internal/parser.rs

@@ -146,7 +146,7 @@ impl<'a> Parser<'a> {
                 out.push_str(&format!("{}\n", failed.red()));
 
                 // Expected Token: list expected tokens
-                out.push_str(&format!("Expected Token: {}\n", expected.to_string()));
+                out.push_str(&format!("Expected Token: {}\n", expected));
 
                 out
             }