Error handling and small editor

- Error handling to signal what is preventing evaluation instead of
  program crash
- Small editor feature (allow edit new
line of code to complete the previous ones instead of destroying the
input, if an empty line inserted return the error preventing evaluation
- Auto indentation on multiline input based on depth

Still does not parse multi-statement code
- This is a problem when dealing with macros: does not allow
  expressions like `'()` since the atomic `'` hides the list ().
  Need to chose between:
  - Replace `'...` with `(quote ... )` during tokenization (may be
    hard to implement macros later)
  - Allows multi-statement code (this also allows to execute multiple
    statements when reading a file)

Will probably delete auto-indentation since it breaks code's uniformity
too much

src/main.rs

@@ -15,9 +15,34 @@ fn main() -> io::Result<()> {
         let _ = io::stdout().flush();
 
         let mut input = String::new();
+        loop {
+            // Read line to compose program inpug
+            let mut line = String::new();
+            io::stdin().read_line(&mut line)?;
 
-        io::stdin().read_line(&mut input)?;
+            // Append line to input
+            input.push_str(&line);
 
-        println!("{}", rep(&input.replace("\n", " ")));
+            // If there is nothing to evaluate skip rep
+            if input == "\n" {
+                continue;
+            }
+
+            // Perform rep on whole available input
+            match rep(&input) {
+                Ok(output) => println!("{}", output),
+                Err((err, depth)) => {
+                    if line == "\n" {
+                        println!("ERROR: {}", err);
+                    } else {
+                        print!("user> {}", "  ".repeat(depth));
+                        // Flush the prompt to appear before command
+                        let _ = io::stdout().flush();
+                        continue;
+                    }
+                }
+            }
+            break;
+        }
     }
 }

src/printer.rs

@@ -1,30 +1,39 @@
+use crate::types::escape_str;
 use crate::types::MalType;
+use crate::types::MalType::*;
 
-pub fn pr_str(ast: &MalType) -> String {
+pub fn pr_str(ast: &MalType, print_readably: bool) -> String {
     match ast {
-        MalType::Nil => "nil".to_string(),
-        MalType::Symbol(sym) => sym.to_string(),
-        MalType::Integer(val) => val.to_string(),
-        MalType::Bool(val) => val.to_string(),
-        MalType::List(el) => format!(
+        Nil => "nil".to_string(),
+        Symbol(sym) | Keyword(sym) => sym.to_string(),
+        Int(val) => val.to_string(),
+        Bool(val) => val.to_string(),
+        Str(str) => {
+            if print_readably {
+                escape_str(str)
+            } else {
+                str.to_string()
+            }
+        }
+        List(el) => format!(
             "({})",
             el.iter()
-                .map(|sub| pr_str(sub))
+                .map(|e| pr_str(e, print_readably))
                 .collect::<Vec<String>>()
                 .join(" ")
         ),
         // This is truly horrible
-        MalType::Vector(el) => format!(
+        Vector(el) => format!(
             "[{}]",
             el.iter()
-                .map(|sub| pr_str(sub))
+                .map(|e| pr_str(e, print_readably))
                 .collect::<Vec<String>>()
                 .join(" ")
         ),
-        MalType::Map(el) => format!(
+        Map(el) => format!(
             "{{{}}}",
             el.iter()
-                .map(|sub| vec![pr_str(sub.0), pr_str(sub.1)].join(" "))
+                .map(|sub| vec![sub.0.to_string(), pr_str(sub.1, print_readably)].join(" "))
                 .collect::<Vec<String>>()
                 .join(" ")
         ),

src/reader.rs

@@ -1,38 +1,43 @@
-use std::collections::{BTreeMap, VecDeque};
-
-use crate::types::MalType;
+// Specyfy components in "types"
+use crate::types::*;
+// By specifying enum variants it's possible to omit namespace
+use crate::types::MalType::*;
 
 use regex::Regex;
 
 pub struct Reader {
-    tokens: VecDeque<String>,
+    tokens: Vec<String>,
+    ptr: usize,
+    depth: usize,
 }
 
 // TODO: instead of panic on missing ")" try implementing a multi line parsing
 // Status on return should always be The last element of the last opened lists
 // (append to the "last" list) while traversing
-const PAREN_ERROR: &str =
-    "Looks like you reached a dead end, did you perhaps miss any \")\" or left some extra \"(\"?";
-
 impl Reader {
-    fn new(tokens: VecDeque<String>) -> Reader {
-        Reader { tokens }
+    fn new(tokens: Vec<String>) -> Reader {
+        Reader {
+            tokens,
+            ptr: 0,
+            depth: 0,
+        }
     }
 
-    /// Returns the token at the current positioni
-    fn peek(&self) -> &str {
-        match self.tokens.get(0) {
-            Some(token) => token,
-            None => panic!("{}", PAREN_ERROR),
+    /// Returns the token at the current position
+    fn peek(&self) -> Result<String, MalErr> {
+        match self.tokens.get(self.ptr) {
+            Some(token) => Ok(token.to_string()),
+            None => Err("Unexpected EOF, Missing parenthesis?".to_string()),
         }
     }
 
     /// Returns the token at current position and increment current position
     // TODO: PLEASE USE THE PEEK FUNCTION
-    fn next(&mut self) -> String {
-        match self.tokens.pop_front() {
-            Some(token) => token,
-            None => panic!("{}", PAREN_ERROR),
+    fn next(&mut self) -> Result<String, MalErr> {
+        self.ptr += 1;
+        match self.tokens.get(self.ptr - 1) {
+            Some(token) => Ok(token.to_string()),
+            None => Err("Unexpected EOF, Missing parenthesis?".to_string()),
         }
     }
 
@@ -41,35 +46,54 @@ impl Reader {
     /// Accumulates results into a MalList
     /// NOTE: `read_list` calls `read_form` -> enable recursion
     /// (lists can contains other lists)
-    fn read_list(&mut self, terminator: &str) -> Vec<MalType> {
-        std::iter::from_fn(|| match self.peek() {
-            ")" | "]" | "}" => {
-                if terminator != self.peek() {
-                    panic!("Unexpected token: {}", self.peek())
+    fn read_list(&mut self, terminator: &str) -> MalRet {
+        self.depth += 1;
+
+        self.next()?;
+
+        let mut vector = Vec::new();
+        loop {
+            let token = self.peek()?;
+            if token == terminator {
+                break;
             }
-                self.next();
-                None
+            vector.push(self.read_form()?)
         }
-            _ => Some(self.read_form()),
-        })
-        .collect()
+        self.next()?;
+        let ret = match terminator {
+            ")" => Ok(List(vector)),
+            "]" => Ok(Vector(vector)),
+            "}" => make_map(vector),
+            _ => Err(format!("Unknown collection terminator: {}", terminator)),
+        };
+        self.depth -= 1;
+        ret
     }
 
     /// Read atomic token and return appropriate scalar ()
-    fn read_atom(&mut self) -> MalType {
-        let token = self.next();
-        // parse the token as an integer
-        match token.parse::<i32>() {
-            // On success assign the value
-            Ok(value) => MalType::Integer(value),
-            // Otherwise assign the symbol
-            Err(_) => match token.as_str() {
-                ")" | "]" | "}" => panic!("Lone parenthesis {}", token),
-                "false" => MalType::Bool(false),
-                "true" => MalType::Bool(true),
-                "nil" => MalType::Nil,
-                _ => MalType::Symbol(token),
-            },
+    fn read_atom(&mut self) -> MalRet {
+        let token = self.next()?;
+        let re_digits = Regex::new(r"^-?[0-9]+$").unwrap();
+        match token.as_str() {
+            ")" | "]" | "}" => Err(format!("Lone parenthesis {}", token)),
+            "false" => Ok(Bool(false)),
+            "true" => Ok(Bool(true)),
+            "nil" => Ok(Nil),
+            _ => {
+                if re_digits.is_match(&token) {
+                    Ok(Int(token.parse::<isize>().unwrap()))
+                } else if token.starts_with('\"') {
+                    if token.ends_with('\"') {
+                        Ok(Str(unescape_str(&token)))
+                    } else {
+                        Err("Unterminated string, expected \"".to_string())
+                    }
+                } else if token.starts_with(':') {
+                    Ok(Keyword(token))
+                } else {
+                    Ok(Symbol(token))
+                }
+            }
         }
     }
 
@@ -78,31 +102,14 @@ impl Reader {
     /// Switch on the first character
     /// "(" -> call `read_list`
     /// otherwise  -> call `read_atom`
-    fn read_form(&mut self) -> MalType {
-        match self.peek() {
+    fn read_form(&mut self) -> MalRet {
+        let token = self.peek()?;
+        // String slice containing the whole string
+        match &token[..] {
             // Consume "(" and parse list
-            "(" => {
-                self.next();
-                MalType::List(self.read_list(")"))
-            }
-            "[" => {
-                self.next();
-                MalType::Vector(self.read_list("]"))
-            }
-            "{" => {
-                self.next();
-                // fallback to C mode for now 😎
-                let list = self.read_list("}");
-                if list.len() % 2 != 0 {
-                    panic!("Missing Map element")
-                }
-                let mut map = BTreeMap::new();
-                for i in (0..list.len()).step_by(2) {
-                    map.insert(list[i].clone(), list[i + 1].clone());
-                }
-                MalType::Map(map)
-            }
-            // read atomically
+            "(" => self.read_list(")"),
+            "[" => self.read_list("]"),
+            "{" => self.read_list("}"),
             _ => self.read_atom(),
         }
     }
@@ -112,23 +119,36 @@ impl Reader {
 /// Create anew Reader with the tokens
 /// Call read_from with the reader instance
 /// TODO: catch errors
-pub fn read_str(input: &str) -> MalType {
-    let ast = Reader::new(tokenize(input)).read_form();
-    // pretty_print(&ast, 0);
-    ast
+pub fn read_str(input: &str) -> Result<MalType, (MalErr, usize)> {
+    let tokens = tokenize(input);
+    match tokens.len() {
+        0 => Ok(Nil),
+        _ => {
+            let mut reader = Reader::new(tokens);
+            match reader.read_form() {
+                Err(err) => Err((err, reader.depth)),
+                Ok(any) => Ok(any),
+            }
+        }
+    }
 }
 
 /// Read a string and return a list of tokens in it (following regex in README)
 // Add error handling for strings that are not terminated
-fn tokenize(input: &str) -> VecDeque<String> {
-    let mut tokens = VecDeque::new();
+fn tokenize(input: &str) -> Vec<String> {
+    let mut tokens = Vec::new();
 
-    let re =
-        Regex::new(r###"[\s,]*(~@|[\[\]{}()'`~^@]|"(?:\\.|[^\\"])*"?|;.*|[^\s\[\]{}('"`,;)]*)"###)
+    let re = Regex::new(
+        r###"[\s,]*(~@|[\[\]{}()'`~^@]|"(?:\\.|[^\\"])*"?|;.*\n|[^\s\[\]{}('"`,;)]*)"###,
+    )
     .unwrap();
     for match_str in re.captures_iter(input) {
-        if match_str[1].len() > 0 {
-            tokens.push_back(match_str[1].to_string());
+        if !match_str[1].is_empty() {
+            // Drop comments
+            if match_str[1].starts_with(';') {
+                continue;
+            }
+            tokens.push(match_str[1].to_string());
         }
     }
 

src/step1_read_print.rs

@@ -6,12 +6,15 @@
 
 use crate::printer::pr_str;
 use crate::reader::read_str;
-use crate::types::MalType;
+use crate::types::{MalErr, MalType};
 
 #[allow(non_snake_case)]
 /// Read input and generate an ast
-fn READ(input: &str) -> MalType {
-    read_str(input)
+fn READ(input: &str) -> Result<MalType, (MalErr, usize)> {
+    match read_str(input) {
+        Ok(ast) => Ok(ast),
+        Err((err, depth)) => Err((format!("Unexpected error during READ: {}", err), depth)),
+    }
 }
 
 #[allow(non_snake_case)]
@@ -24,11 +27,11 @@ fn EVAL(ast: MalType) -> MalType {
 #[allow(non_snake_case)]
 /// Print out the result of the evaluation
 fn PRINT(input: MalType) -> String {
-    pr_str(&input)
+    pr_str(&input, true)
 }
 
-pub fn rep(input: &str) -> String {
-    let ast = READ(input);
+pub fn rep(input: &str) -> Result<String, (MalErr, usize)> {
+    let ast = READ(input)?;
     let out = EVAL(ast);
-    PRINT(out /*&result*/)
+    Ok(PRINT(out))
 }

src/types.rs

@@ -1,16 +1,69 @@
 // TODO: use enums for MalTypes
 
-use std::collections::BTreeMap;
+use std::collections::HashMap;
 
 // All Mal types should inherit from this
-#[derive(Debug, Ord, Eq, PartialEq, PartialOrd, Clone)]
+#[derive(Debug, Clone)]
 pub enum MalType {
     List(Vec<MalType>),
     Vector(Vec<MalType>),
-    // HashMap cannot implement Hash
-    Map(BTreeMap<MalType, MalType>),
+    Map(HashMap<String, MalType>),
     Symbol(String),
-    Integer(i32),
+    Keyword(String),
+    Str(String),
+    Int(isize),
     Bool(bool),
     Nil,
 }
+
+// Stolen, but this way it's easier to handle errors
+
+/*
+#[derive(Debug)]
+pub enum MalErr {
+    Str(String), // Messages to the user
+                 // Val(MalType),
+                 // Messages to the program
+} TEMP TEMP  */
+pub type MalErr = String;
+
+pub type MalArgs = Vec<MalType>;
+pub type MalRet = Result<MalType, MalErr>;
+
+use MalType::{Map, Symbol};
+
+pub fn make_map(list: MalArgs) -> MalRet {
+    if list.len() % 2 != 0 {
+        return Err("Map length is odd: missing value".to_string());
+    }
+
+    let mut map = HashMap::new();
+
+    for i in (0..list.len()).step_by(2) {
+        match &list[i] {
+            Symbol(k) => {
+                let v = list[i + 1].clone();
+                map.insert(k.to_string(), v);
+            }
+            _ => return Err(format!("Map key not valid: {:?}", list[i])),
+        }
+    }
+    Ok(Map(map))
+}
+
+pub fn escape_str(s: &str) -> String {
+    format!(
+        "\"{}\"",
+        String::from(s)
+            .replace('\\', "\\\\")
+            .replace('\n', "\\n")
+            .replace('\"', "\\\"")
+    )
+}
+
+pub fn unescape_str(s: &str) -> String {
+    String::from(&s[1..s.len() - 1])
+        .replace("\\\\", "\\")
+        .replace("\\n", "\n")
+        .replace("\\\"", "\"")
+}