✨ variable declaration.

doc/grammar.bnf

@@ -1,8 +1,21 @@
 MODULE ::= INSTR*
-INSTR ::= EXPR semicolon
+INSTR ::=
-EXPR ::= BUILTIN
+| EXPR semicolon
+| ASSIGN semicolon
+| ASSIGN_IF semicolon
+| ASSIGN_ADD semicolon
+ASSIGN ::= ident assign EXPR
+ASSIGN_IF ::= ident assign_if EXPR
+ASSIGN_ADD ::= ident assign_add EXPR
+EXPR ::= LITERAL
+LITERAL ::= 
+| BUILTIN 
+| ARRAY 
+| ident
 BUILTIN ::= 
 | bool 
 | float 
 | int
 | string
+
+ARRAY ::= osquare EXPR* csquare

src/ast/lexer.rs

@@ -19,7 +19,8 @@ impl Lexer {
             line: 1,
             text: String::from(""),
             separators: vec![
-                ';'
+                ';', '[', ']',
+                '=', '?', '+'
             ]
         }
     }
@@ -38,21 +39,71 @@ impl Lexer {
         self.line = 1;
     }
 
+    pub fn peek(&mut self, lookahead: i32) -> Option<Node> {
+        let cursor = self.cursor;
+        let line = self.line;
+
+        let mut node: Option<Node> = None;
+
+        for _ in 0..=lookahead {
+            node = self.next();
+        }
+        
+        self.cursor = cursor;
+        self.line = line;
+        node
+    }
+
+    fn is_char_sep(&self, c: char) -> bool {
+        let el = self.separators.iter().find(|&&x| x == c);
+
+        if el.is_some() {
+            return true;
+        }
+
+        return c.is_whitespace();
+    }
+
     fn is_sep(&self, pos: usize) -> bool {
         if let Some(c) = self.text.chars().nth(pos) {
-
+            return self.is_char_sep(c);
-            let el = self.separators.iter().find(|&&x| x == c);
-
-            if el.is_some() {
-                return true;
-            }
-
-            return c.is_whitespace();
         }
 
         false
     }
 
+    fn scan_identifier(&mut self) -> Option<Token> {
+        let mut value = String::from("");
+        let mut first = true;
+
+        for c in self.text.chars().skip(self.cursor) {
+            if self.is_char_sep(c) {
+                break;
+            }
+
+            if first && c.is_digit(10) {
+                break;
+            }
+
+            if !c.is_ascii_alphabetic() && c != '_' 
+            && !c.is_digit(10) {
+                break;
+            }
+
+            value.push(c);
+            first = false;
+        }
+
+        if value.len() > 0 {
+            return Some(Token {
+                position: self.cursor + value.len(),
+                value
+            });
+        }
+
+        None
+    }
+
     fn scan_string(&mut self) -> Option<Token> {
         let mut value : String;
         let mut length = 1;
@@ -62,7 +113,7 @@ impl Lexer {
         } else {
             return None;
         }
-        
+
         let mut escape = false;
         let mut closed = false;
 
@@ -71,7 +122,7 @@ impl Lexer {
                 escape = true;
                 length += 1;
                 continue;
-            } 
+            }
 
             if escape {
                 match c {
@@ -80,7 +131,7 @@ impl Lexer {
                     'n' => value.push('\n'),
                     't' => value.push('\t'),
                     'r' => value.push('\r'),
-                    _ => {} 
+                    _ => {}
                 }
             } else if c == '"' {
                 closed = true;
@@ -105,7 +156,7 @@ impl Lexer {
 
     fn scan_int(&self) -> Option<Token> {
         let mut value = String::from("");
-        
+
         if let Some('-') = self.text.chars().nth(self.cursor) {
             value.push('-');
         }
@@ -117,7 +168,7 @@ impl Lexer {
                 break;
             }
         }
-        
+
         if value.len() > 0 {
             Some(Token {
                 position: self.cursor + value.len(),
@@ -125,12 +176,12 @@ impl Lexer {
             })
         } else {
             None
-        } 
+        }
     }
 
     fn scan_float(&self) -> Option<Token> {
         let mut value = String::from("");
-        
+
         if let Some('-') = self.text.chars().nth(self.cursor) {
             value.push('-');
         }
@@ -142,7 +193,7 @@ impl Lexer {
                 break;
             }
         }
-        
+
         if let Some('.') = self.text.chars().nth(self.cursor + value.len()) {
             value.push('.');
         } else {
@@ -156,7 +207,7 @@ impl Lexer {
                 break;
             }
         }
-        
+
         if value.len() > 0 && value != "." {
             if value.chars().nth(0).unwrap() == '.' {
                 value = format!("0{}", value);
@@ -172,7 +223,7 @@ impl Lexer {
             })
         } else {
             None
-        } 
+        }
     }
 
     fn scan_text(&self, text: &str) -> Option<Token> {
@@ -231,6 +282,21 @@ impl Lexer {
             self.cursor += 1;
         }
     }
+
+    fn skip_comments(&mut self) {
+        while let Some('#') = self.text.chars().nth(self.cursor) {
+            loop {
+                if let Some('\n')
+                = self.text.chars().nth(self.cursor) {
+                    break;
+                }
+
+                self.cursor += 1;
+            }
+
+            self.skip_spaces();
+        }
+    }
 }
 
 impl Iterator for Lexer {
@@ -238,6 +304,32 @@ impl Iterator for Lexer {
 
     fn next(&mut self) -> Option<Self::Item> {
         self.skip_spaces();
+        self.skip_comments();
+
+        if let Some(token) = self.scan_text("+=") {
+            self.cursor = token.position;
+            return Some(Node::AssignAdd);
+        }
+
+        if let Some(token) = self.scan_text("?=") {
+            self.cursor = token.position;
+            return Some(Node::AssignIf);
+        }
+
+        if let Some(token) = self.scan_text("=") {
+            self.cursor = token.position;
+            return Some(Node::Assign);
+        }
+
+        if let Some(token) = self.scan_text("[") {
+            self.cursor = token.position;
+            return Some(Node::OSquare);
+        }
+
+        if let Some(token) = self.scan_text("]") {
+            self.cursor = token.position;
+            return Some(Node::CSquare);
+        }
 
         if let Some(token) = self.scan_keyword("true") {
             self.cursor = token.position;
@@ -273,6 +365,11 @@ impl Iterator for Lexer {
             }
         }
 
+        if let Some(token) = self.scan_identifier() {
+            self.cursor = token.position;
+            return Some(Node::Ident(token.value.clone()));
+        }
+
         None
     }
 }
@@ -324,13 +421,12 @@ mod test {
     }
 
     #[test]
-    fn test_wrong_ident() {
+    fn test_identifier() {
         let mut lex = Lexer::new();
-        let res = lexer_run(&mut lex, " truea ");
+        let res = lexer_run(&mut lex, " truea atrue ").unwrap();
-        assert!(res.is_err());
+        assert_eq!(2, res.len());
-        let mut lex = Lexer::new();
+        assert_eq!(Node::Ident(String::from("truea")), *res.get(0).unwrap());
-        let res = lexer_run(&mut lex, " atrue ");
+        assert_eq!(Node::Ident(String::from("atrue")), *res.get(1).unwrap());
-        assert!(res.is_err());
     }
 
     #[test]
@@ -349,7 +445,7 @@ mod test {
         assert_eq!(Node::Semicolon, *res.get(1).unwrap());
         Ok(())
     }
-    
+
     #[test]
     fn test_integers() -> Result<(), error::AstError> {
         let mut lex = Lexer::new();
@@ -378,14 +474,58 @@ mod test {
     #[test]
     fn test_string() -> Result<(), error::AstError> {
         let mut lex = Lexer::new();
-        
+
-        let res = lexer_run(&mut lex, 
+        let res = lexer_run(&mut lex,
             " \"s\\ta\\\"lut\\n\" ")?;
 
         assert_eq!(1, res.len());
-        assert_eq!(Node::String(String::from("s\ta\"lut\n")), 
+        assert_eq!(Node::String(String::from("s\ta\"lut\n")),
             *res.get(0).unwrap());
-        
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_comments() -> Result<(), error::AstError> {
+        let mut lex = Lexer::new();
+
+        let res = lexer_run(&mut lex,
+            " # aze \n 4 ")?;
+
+        assert_eq!(1, res.len());
+        assert_eq!(Node::Int(4),
+            *res.get(0).unwrap());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_arrays() -> Result<(), error::AstError> {
+        let mut lex = Lexer::new();
+
+        let res = lexer_run(&mut lex,
+            " [ ] ")?;
+
+        assert_eq!(2, res.len());
+        assert_eq!(Node::OSquare, *res.get(0).unwrap());
+        assert_eq!(Node::CSquare, *res.get(1).unwrap());
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_variables() -> Result<(), error::AstError> {
+        let mut lex = Lexer::new();
+
+        let res = lexer_run(&mut lex,
+            " = ?= += ananas ")?;
+
+        assert_eq!(4, res.len());
+        assert_eq!(Node::Assign, *res.get(0).unwrap());
+        assert_eq!(Node::AssignIf, *res.get(1).unwrap());
+        assert_eq!(Node::AssignAdd, *res.get(2).unwrap());
+        assert_eq!(Node::Ident(String::from("ananas")), *res.get(3).unwrap());
+
         Ok(())
     }
 }

src/ast/node.rs

@@ -6,6 +6,16 @@ pub enum Node {
     Int(i32),
     Float(f64),
     String(String),
+    OSquare,
+    CSquare,
+    Array(Vec<Node>),
+    Assign,
+    AssignIf,
+    AssignAdd,
+    AssignInstr(Box<Node>, Vec<Node>),
+    AssignIfInstr(Box<Node>, Vec<Node>),
+    AssignAddInstr(Box<Node>, Vec<Node>),
+    Ident(String),
     Semicolon
 }
 

src/ast/parser.rs

@@ -45,51 +45,143 @@ impl Parser {
         Ok(Some(n))
     }
 
+    fn ensure_semicolon(&mut self, result: ParseResult)
+        -> ParseResult {
+        match self.lexer.next() {
+            Some(Node::Semicolon) => result,
+            _ => Err(error::AstError {
+                msg: String::from("missing semicolon"),
+                line: self.lexer.line()})
+        }
+    }
+
     fn parse_instr(&mut self) -> ParseResult {
-        match self.parse_expr() {
+        match self.lexer.peek(1) {
-            Ok(Some(expr)) => {
+            Some(Node::Assign) => {
-                match self.lexer.next() {
+                    let assign = self.parse_assign();
-                    Some(Node::Semicolon) => Ok(Some(expr)),
+                    self.ensure_semicolon(assign)
-                    None => Ok(None),
-                    _ => Err(error::AstError {
-                        msg: String::from("missing semicolon"),
-                        line: self.lexer.line()})
-                }
             },
-            Err(err) => { Err(err) },
+
-            Ok(None) => Ok(None)
+            Some(Node::AssignIf) => {
+                    let assign = self.parse_assign_if();
+                    self.ensure_semicolon(assign)
+            },
+
+            Some(Node::AssignAdd) => {
+                    let assign = self.parse_assign_add();
+                    self.ensure_semicolon(assign)
+            },
+
+            _ =>
+                match self.parse_expr() {
+                    Ok(Some(expr)) =>
+                        self.ensure_semicolon(Ok(Some(expr))),
+                    Err(err) => { Err(err) },
+                    Ok(None) => Ok(None)
+                }
+        }
+    }
+
+    fn assign_helper(&mut self)
+            -> Result<(Box<Node>, Vec<Node>), error::AstError> {
+        let mut rhs: Vec<Node> = vec![];
+
+        if let Some(Node::Ident(value)) = self.lexer.next() {
+            let _assign = self.lexer.next();
+
+            loop {
+                match self.lexer.peek(0) {
+                    Some(Node::Semicolon) | None => {
+                        break;
+                    },
+
+                    Some(v) => { self.lexer.next(); rhs.push(v); }
+                }
+            }
+
+            Ok((Box::new(Node::Ident(value)), rhs))
+
+        } else {
+            Err(error::AstError {
+                msg: String::from("cannot assign value to node"),
+                line: self.lexer.line()
+            })
+        }
+    }
+
+    fn parse_assign(&mut self) -> ParseResult {
+        match self.assign_helper() {
+            Ok((lhs, rhs)) 
+                => Ok(Some(Node::AssignInstr(lhs, rhs))),
+            Err(err) => Err(err)
+        }
+    }
+
+    fn parse_assign_if(&mut self) -> ParseResult {
+        match self.assign_helper() {
+            Ok((lhs, rhs)) 
+                => Ok(Some(Node::AssignIfInstr(lhs, rhs))),
+            Err(err) => Err(err)
+        }
+    }
+
+    fn parse_assign_add(&mut self) -> ParseResult {
+        match self.assign_helper() {
+            Ok((lhs, rhs)) 
+                => Ok(Some(Node::AssignAddInstr(lhs, rhs))),
+            Err(err) => Err(err)
         }
     }
 
     fn parse_expr(&mut self) -> ParseResult {
-        self.parse_builtin()
+        self.parse_literal()
     }
 
+    fn parse_literal(&mut self) -> ParseResult {
+        match self.lexer.peek(0) {
+            Some(Node::Ident(id)) 
+                => { self.lexer.next(); Ok(Some(Node::Ident(id))) },
+            Some(Node::OSquare) => self.parse_array(),
+            Some(_) => self.parse_builtin(),
+            None => { self.lexer.next(); Ok(None) }
+        }
+    }
 
     fn parse_builtin(&mut self) -> ParseResult {
-        match self.lexer.next() {
+        let node = self.lexer.next().unwrap();
-            Some(Node::Int(value))
+        match node {
+            Node::Int(value)
                 => Ok(Some(Node::Int(value))),
 
-            Some(Node::Float(value))
+            Node::Float(value)
                 => Ok(Some(Node::Float(value))),
 
-            Some(Node::Bool(value))
+            Node::Bool(value)
                 => Ok(Some(Node::Bool(value))),
 
-            Some(Node::String(value))
+            Node::String(value)
                 => Ok(Some(Node::String(value))),
 
-            Some(other) => {
+            _ => {
                 Err(error::AstError {
-                    msg: String::from(format!("unexpected {:?}", other)),
+                    msg: String::from(format!("unexpected {:?}", node)),
                     line: self.lexer.line()
                 })
             }
-
-            None => Ok(None)
         }
     }
+
+    fn parse_array(&mut self) -> ParseResult {
+        let mut elements: Vec<Node> = vec![];
+
+        let _osquare = self.lexer.next();
+
+        while let Ok(Some(expr)) = self.parse_expr() {
+            elements.push(expr);
+        }
+
+        Ok(Some(Node::Array(elements)))
+    }
 }
 
 #[cfg(test)]
@@ -179,4 +271,59 @@ mod test {
 
         Ok(())
     }
+
+    #[test]
+    fn assign_variables() -> TestResult {
+        test_parser(
+            Node::Module("mod".to_owned(), vec![
+                Node::AssignInstr(
+                    Box::new(Node::Ident(String::from("HELLO"))),
+                    vec![Node::Int(4), Node::Bool(true)]
+                )
+            ]),
+            " HELLO = 4 true; "
+        )?;
+
+        test_parser(
+            Node::Module("mod".to_owned(), vec![
+                Node::AssignIfInstr(
+                    Box::new(Node::Ident(String::from("HELLO_2"))),
+                    vec![Node::Int(4)]
+                )
+            ]),
+            " HELLO_2 ?= 4; "
+        )?;
+
+        test_parser(
+            Node::Module("mod".to_owned(), vec![
+                Node::AssignAddInstr(
+                    Box::new(Node::Ident(
+                        String::from("HELLO_WORLD"))
+                    ),
+                    vec![
+                        Node::Int(4),
+                        Node::Int(1),
+                        Node::Int(2)
+                    ]
+                )
+            ]),
+            " HELLO_WORLD += 4 1 2; "
+        )?;
+        Ok(())
+    }
+    #[test]
+    fn arrays() -> TestResult {
+        test_parser(
+            Node::Module("mod".to_owned(), vec![
+                Node::Array(vec![
+                    Node::Int(2),
+                    Node::Float(3.2),
+                    Node::Bool(true)
+                ])
+            ]),
+            " [2 3.2 true]; "
+        )?;
+
+        Ok(())
+    }
 }

src/eval/evaluator.rs

@@ -2,12 +2,13 @@ use crate::{
     ast::node::Node,
     eval::{
         value::Value,
-        error::EvalError
+        error::EvalError,
+        symtable::SymTable
     }
 };
 
 pub struct Evaluator {
-
+    table: SymTable
 }
 
 type EvalResult = Result<Option<Value>, EvalError>;
@@ -15,6 +16,7 @@ type EvalResult = Result<Option<Value>, EvalError>;
 impl Evaluator {
     pub fn new() -> Self {
         Self {
+            table: SymTable::new()
         }
     }
 
@@ -29,15 +31,158 @@ impl Evaluator {
 
                 Ok(res)
             },
-            
+
+            Node::Ident(name) => {
+                match self.table.get(name) {
+                    Some(val) => {
+                        Ok(Some(val))
+                    },
+
+                    None => Err(EvalError {
+                        msg: format!("cannot find <{}>", name),
+                        line: 0
+                    })
+                }
+            },
+
+            Node::AssignAddInstr(target, values) => {
+                match &**target {
+                    Node::Ident(name) => {
+                        let mut val_array: Vec<Value> = vec![];
+
+                        match self.table.get(name) {
+                            Some(Value::Array(existing_arr)) => {
+                                val_array = existing_arr;
+                            },
+                            Some(val) => {
+                                val_array.push(val);
+                            },
+                            None => {
+                            }
+                        }
+
+                        for node_val in values {
+                            let val = self.run(node_val)?;
+                            if let Some(v) = val {
+                                val_array.push(v);
+                            }
+                        }
+
+                        let value = Value::Array(val_array);
+                        self.table.set(name, value);
+                    },
+                    _ => {
+                        return Err(EvalError {
+                            msg: format!(
+                                "cannot assign to target <{:?}>",
+                                target
+                            ),
+                            line: 0
+                        });
+                    }
+                }
+
+                Ok(None)
+            },
+
+            Node::AssignIfInstr(target, values) => {
+                match &**target {
+                    Node::Ident(name) => {
+                        match self.table.get(name) {
+                            Some(_) => {},
+                            None => {
+                                if let Some(value)
+                                    = self.nodes_to_value(values)? {
+                                    self.table.set(name, value);
+                                }
+                            }
+                        }
+                    },
+                    _ => {
+                        return Err(EvalError {
+                            msg: format!(
+                                "cannot assign to target <{:?}>",
+                                target
+                            ),
+                            line: 0
+                        });
+                    }
+                }
+
+                Ok(None)
+            },
+
+            Node::AssignInstr(target, values) => {
+                match &**target {
+                    Node::Ident(name) => {
+                        if let Some(value) = self.nodes_to_value(values)? {
+                            self.table.set(name, value);
+                        }
+                    },
+                    _ => {
+                        return Err(EvalError {
+                            msg: format!(
+                                "cannot assign to target <{:?}>",
+                                target
+                            ),
+                            line: 0
+                        });
+                    }
+                }
+
+                Ok(None)
+            },
+
             Node::Bool(value) => Ok(Some(Value::Bool(*value))),
             Node::Int(value) => Ok(Some(Value::Int(*value))),
             Node::Float(value) => Ok(Some(Value::Float(*value))),
-            Node::String(value) => Ok(Some(Value::String(value.clone()))),
+            Node::String(value)
+                => Ok(Some(Value::String(value.clone()))),
+            Node::Array(nodes) => {
+                let mut values: Vec<Value> = vec![];
+
+                for node in nodes {
+                    match self.run(node) {
+                        Ok(Some(value)) => {
+                            values.push(value);
+                        },
+
+                        _ => {
+                            return Err(EvalError {
+                                msg: String::from("invalid array element"),
+                                line: 0
+                            });
+                        }
+                    }
+                }
+
+                Ok(Some(Value::Array(values)))
+            }
 
             _ => Ok(None)
         }
     }
+
+    fn nodes_to_value(&mut self, nodes: &Vec<Node>) -> EvalResult {
+        let mut val_array: Vec<Value> = vec![];
+
+        for node in nodes {
+            match self.run(node) {
+                Ok(Some(val)) => val_array.push(val),
+                Ok(None) => {},
+                Err(err) => { return Err(err); }
+            }
+        }
+
+        if val_array.len() == 0 {
+            Ok(None)
+        } else if val_array.len() == 1 {
+            let val = val_array.get(0).unwrap();
+            Ok(Some(val.clone()))
+        } else {
+            Ok(Some(Value::Array(val_array)))
+        }
+    }
 }
 
 #[cfg(test)]
@@ -80,6 +225,24 @@ mod test {
         }
     }
 
+    fn test_eval_fail(source: &str) -> TestResult {
+        let mut lex = Lexer::new();
+        lex.prepare(source);
+
+        let mut parser = Parser::new("mod", lex);
+        let root = parser.run()?.unwrap();
+
+        let mut evaluator = Evaluator::new();
+
+        match evaluator.run(&root) {
+            Err(_) => Ok(()),
+            _ => Err(Box::new(EvalError {
+                msg: format!("\"{}\" should fail", source),
+                line: 0
+            }))
+        }
+    }
+
     #[test]
     fn simple_boolean() -> TestResult {
         test_eval_value(Value::Bool(true), " true; false; true; ")?;
@@ -98,9 +261,98 @@ mod test {
 
     #[test]
     fn strings() -> TestResult {
-        test_eval_value(Value::String(String::from(" pizzza!!!")), 
+        test_eval_value(Value::String(String::from(" pizzza!!!")),
             " \" pizzza!!!\"; ")?;
 
         Ok(())
     }
+
+    #[test]
+    fn arrays() -> TestResult {
+        test_eval_value(
+            Value::Array(
+                vec![
+                    Value::Int(2),
+                    Value::Int(4),
+                    Value::Float(6.1)
+                ]
+            ),
+            " [2 4 6.1]; ")?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn simple_variable() -> TestResult {
+        test_eval_fail("X = V;")?;
+
+        test_eval_value(
+            Value::Int(4),
+            " X = 4; X; ")?;
+
+        test_eval_value(
+            Value::Float(7.2),
+            " X = 4; X = 7.2; X; ")?;
+
+        test_eval_value(
+            Value::Array(
+                vec![
+                    Value::Int(4),
+                    Value::Int(9),
+                    Value::Float(5.2),
+                ]
+            ),
+            " X = 4 9 5.2; X; ")?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn variable_assign_if() -> TestResult {
+        test_eval_fail(" X ?= V; ")?;
+
+        test_eval_value(
+            Value::Int(4),
+            " X ?= 4; X; ")?;
+
+        test_eval_value(
+            Value::Int(4),
+            " X ?= 4; X ?= 9; X; ")?;
+
+        Ok(())
+    }
+
+    #[test]
+    fn variable_assign_add() -> TestResult {
+        test_eval_fail("X += V; ")?;
+
+        test_eval_value(
+            Value::Array(
+                vec![
+                    Value::Int(4),
+                ]
+            ),
+            " X += 4; X; ")?;
+
+        test_eval_value(
+            Value::Array(
+                vec![
+                    Value::Int(4),
+                    Value::Float(3.3)
+                ]
+            ),
+            " X = 4; X += 3.3; X; ")?;
+
+        test_eval_value(
+            Value::Array(
+                vec![
+                    Value::Int(4),
+                    Value::Int(1),
+                    Value::Float(3.3)
+                ]
+            ),
+            " X = 4 1; X += 3.3; X; ")?;
+
+        Ok(())
+    }
 }

src/eval/mod.rs

@@ -1,3 +1,4 @@
 pub mod value;
 pub mod evaluator;
 pub mod error;
+pub mod symtable;

src/eval/symtable.rs

@@ -0,0 +1,42 @@
+use crate::eval::value::Value;
+use std::collections::HashMap;
+
+struct Sym {
+    value: Value
+}
+
+pub struct SymTable {
+    table: HashMap<String, Sym>
+}
+
+impl SymTable {
+    pub fn new() -> Self {
+        Self {
+            table: HashMap::new()
+        }
+    }
+
+    pub fn set(&mut self, name: &str, value: Value) {
+        self.table.insert(name.to_owned(), Sym { value });
+    }
+
+    pub fn get(&mut self, name: &str) -> Option<Value> {
+        match self.table.get(name) {
+            Some(sym) => Some(sym.value.clone()),
+            None => None
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn declare_new_value() {
+        let mut sym = SymTable::new();
+        assert!(sym.get("hello").is_none());
+        sym.set("hello", Value::Int(34));
+        assert_eq!(Value::Int(34), sym.get("hello").unwrap());
+    }
+}

src/eval/value.rs

@@ -1,9 +1,11 @@
 #[derive(PartialEq)]
 #[derive(Debug)]
+#[derive(Clone)]
 pub enum Value {
     Bool(bool),
     Int(i32),
     Float(f64),
-    String(String)
+    String(String),
+    Array(Vec<Value>)
 }