Show location of error in parse error

schala-lang/language/src/lib.rs

@@ -90,7 +90,8 @@ impl Schala {
 }
 
 //TODO rejigger the signature of these methods so you don't awkwardly have the input in the middle
-fn load_source<'a>(_handle: &mut Schala, input: &'a str, comp: Option<&mut UnfinishedComputation>) -> Result<&'a str, String> {
+fn load_source<'a>(handle: &mut Schala, input: &'a str, _comp: Option<&mut UnfinishedComputation>) -> Result<&'a str, String> {
+  handle.source_reference.load_new_source(input);
   Ok(input)
 }
 
@@ -131,13 +132,25 @@ fn parsing(handle: &mut Schala, input: Vec<tokenizing::Token>, comp: Option<&mut
       Some(ref x) => println!("Bad parsing debug option: {}", x),
     };
   });
-  ast.map_err(|error: parsing::ParseError| {
-    let location_frag = match error.token {
-      Some(tok) => format!(" at line: {} column: {}", tok.offset.0, tok.offset.1),
-      None => "".into()
-    };
-    format!("'{}'{}", error.msg, location_frag)
-  })
+  ast.map_err(|err| format_parse_error(err, handle))
+}
+
+fn format_parse_error(error: parsing::ParseError, handle: &mut Schala) -> String {
+  //TODO make token no longer be Optoinal
+  if let Some(tok) = error.token {
+    let line = tok.offset.0;
+    let ch = tok.offset.1;
+    let line_from_program = handle.source_reference.get_line(line);
+    let location_pointer = format!("{}^", " ".repeat(ch));
+    format!(r#"
+{}
+|
+| {}
+| {}
+"#, error.msg, line_from_program, location_pointer)
+  } else {
+    format!("{}", error.msg)
+  }
 }
 
 fn symbol_table(handle: &mut Schala, input: ast::AST, comp: Option<&mut UnfinishedComputation>) -> Result<ast::AST, String> {
@@ -183,15 +196,20 @@ fn eval(handle: &mut Schala, input: reduced_ast::ReducedAST, comp: Option<&mut U
 }
 
 struct SourceReference {
-
+  lines: Option<Vec<String>>
 }
 
 impl SourceReference {
   fn new() -> SourceReference {
-    SourceReference { }
+    SourceReference { lines: None }
   }
 
-  fn load_new_source(&mut self, source: String) {
+  fn load_new_source(&mut self, source: &str) {
+    //TODO this is a lot of heap allocations - maybe there's a way to make it more efficient?
+    self.lines = Some(source.lines().map(|s| s.to_string()).collect());
+  }
 
+  fn get_line(&self, line: usize) -> String {
+    self.lines.as_ref().and_then(|x| x.get(line).map(|s| s.to_string())).unwrap_or(format!("NO LINE FOUND"))
   }
 }