Added let statement parser

src/parser/ast/mod.rs

@@ -1,5 +1,6 @@
-use super::ParserError;
-use crate::lexer::Lexer;
+use super::ParseError;
+use crate::lexer::Token;
+use crate::parser::Parser;
 use std::error::Error;
 
 pub trait Node {
@@ -7,8 +8,8 @@ pub trait Node {
     fn validate(&self) -> Result<(), Box<dyn Error>>;
 }
 
-pub trait Statement: Node {
-    fn parse(&mut Lexer) -> Self
+pub(crate) trait Statement: Node {
+    fn parse(&mut Parser) -> Result<Self, Box<dyn Error>>
     where
         Self: Sized;
 }
@@ -21,11 +22,16 @@ pub struct LetStatement {
     // value: dyn Expression,
 }
 
+impl LetStatement {
+    pub fn new(identifier: Identifier) -> LetStatement {
+        LetStatement { name: identifier }
+    }
+}
 impl Node for LetStatement {
     fn validate(&self) -> Result<(), Box<dyn Error>> {
         if self.token_literal() != "let" {
-            return Err(Box::new(ParserError::new(
-                "self.token_literal is not set, got=".to_owned() + self.token_literal(),
+            return Err(Box::new(ParseError::new(
+                &("self.token_literal is not set, got=".to_owned() + self.token_literal()),
             )));
         }
         Ok(())
@@ -37,19 +43,52 @@ impl Node for LetStatement {
 }
 
 impl Statement for LetStatement {
-    fn parse(lexer: &mut Lexer) -> LetStatement {
-        LetStatement {
-            name: Identifier { name: "potato" },
-            // value: "",
+    fn parse(parser: &mut Parser) -> Result<LetStatement, Box<dyn Error>> {
+        let name;
+        //TODO: Add expression parser
+        match parser.lexer.next() {
+            Some(v) => match v {
+                Token::Ident(q) => name = Identifier { name: q },
+                n @ _ => {
+                    return Err(Box::new(ParseError::new(&format!(
+                        "expected IDENT, Found {:?}",
+                        n
+                    ))))
+                }
+            },
+            None => {
+                return Err(Box::new(ParseError::new(
+                    "expected IDENT after let, Could not find it",
+                )))
+            }
+        };
+
+        if !parser.expect_peek(Token::Assign) {
+            return Err(Box::new(ParseError::new("expected =, Could not find it")));
         }
+
+        while !parser.current_token_is(Token::Semicolon) {
+            println!("prev_token={:?}", parser.current_token);
+            parser.current_token = parser.lexer.next();
+            println!("current_token={:?}", parser.current_token);
+        }
+
+        Ok(LetStatement { name })
     }
 }
 
 #[derive(Debug)]
 pub struct Identifier {
-    name: &'static str,
+    name: String,
 }
 
+impl Identifier {
+    pub fn new(name: &str) -> Identifier {
+        Identifier {
+            name: name.to_owned(),
+        }
+    }
+}
 impl Node for Identifier {
     fn validate(&self) -> Result<(), Box<dyn Error>> {
         Ok(())

src/parser/mod.rs

@@ -5,37 +5,76 @@ pub use self::program::Program;
 
 use self::ast::{LetStatement, Statement};
 use crate::lexer::{Lexer, Token};
+use std::iter::Peekable;
 
-struct Parser {}
+pub(crate) struct Parser<'a> {
+    lexer: Peekable<Lexer<'a>>,
+    current_token: Option<Token>,
+}
 
-impl Parser {
-    fn parse_statement(token: Token, lexer: &mut Lexer) -> Option<Box<dyn ast::Statement>> {
-        match token {
-            Token::Let => Some(Box::new(LetStatement::parse(lexer))),
-            _ => unimplemented!(),
+impl<'a> Parser<'a> {
+    fn new(lexer: Lexer<'a>) -> Parser {
+        Parser {
+            lexer: lexer.peekable(),
+            current_token: None,
         }
     }
+    fn parse_statement(&mut self, token: Token) -> Option<Box<dyn ast::Statement>> {
+        match token {
+            Token::Let => {
+                let stmt = match LetStatement::parse(self) {
+                    Ok(v) => v,
+                    Err(_) => return None, //TODO: Return appropriate error
+                };
+
+                Some(Box::new(stmt))
+            }
+            n @ _ => {
+                println!("{:?}", n);
+                None
+            }
+        }
+    }
+
+    fn expect_peek(&mut self, token: Token) -> bool {
+        if let Some(v) = self.lexer.peek() {
+            if v == &token {
+                self.lexer.next();
+                true
+            } else {
+                false
+            }
+        } else {
+            false
+        }
+    }
+
+    fn current_token_is(&self, token: Token) -> bool {
+        self.current_token == Some(token)
+    }
 }
 
 #[derive(Debug)]
-struct ParserError {
+struct ParseError {
     desc: String,
 }
 
-impl std::fmt::Display for ParserError {
+impl std::fmt::Display for ParseError {
     fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
-        write!(f, "ParserError: ")
+        write!(f, "ParseError: {}", self)
     }
 }
 
-impl std::error::Error for ParserError {
+impl std::error::Error for ParseError {
     fn description(&self) -> &str {
         &self.desc
     }
 }
 
-impl ParserError {
-    fn new(desc: String) -> ParserError {
-        ParserError { desc }
+impl ParseError {
+    fn new(desc: &str) -> ParseError {
+        ParseError {
+            desc: desc.to_owned(),
+        }
     }
 }

src/parser/program.rs

@@ -1,5 +1,5 @@
 use crate::lexer::{Lexer, Token};
-use crate::parser::ast::{LetStatement, Statement};
+use crate::parser::ast::Statement;
 use crate::parser::Parser;
 
 pub struct Program {
@@ -7,24 +7,16 @@ pub struct Program {
 }
 
 impl Program {
-    pub fn token_literal(&self) -> &'static str {
-        if self.statements.len() > 0 {
-            self.statements[0].token_literal()
-        } else {
-            ""
-        }
-    }
-
-    pub fn parse(mut lexer: Lexer) -> Program {
+    pub fn parse(lexer: Lexer) -> Program {
         let mut statements = vec![];
-
+        let mut parser = Parser::new(lexer);
         loop {
-            if let Some(token) = lexer.next() {
+            if let Some(token) = parser.lexer.next() {
                 if token == Token::EOF {
                     break;
                 }
 
-                if let Some(stmt) = Parser::parse_statement(token, &mut lexer) {
+                if let Some(stmt) = parser.parse_statement(token) {
                     statements.push(stmt);
                 } else {
                     continue;
@@ -41,8 +33,8 @@ impl Program {
 #[cfg(test)]
 mod tests {
     use crate::lexer::Lexer;
+    use crate::parser::ast::{Identifier, LetStatement};
     use crate::parser::Program;
-
     #[test]
     fn let_statements() {
         let ip = "
@@ -50,12 +42,21 @@ mod tests {
         let qq = 10;
         let foobar = 8388383;
         ";
-
+        let out = Program {
+            statements: vec![
+                Box::new(LetStatement::new(Identifier::new("yr"))),
+                Box::new(LetStatement::new(Identifier::new("qq"))),
+                Box::new(LetStatement::new(Identifier::new("foobar"))),
+            ],
+        };
         let lexer = Lexer::new(ip);
         let ast_tree = Program::parse(lexer);
 
         if ast_tree.statements.len() != 3 {
             assert_eq!(ast_tree.statements.len(), 3);
         }
+        for (out, expected_out) in ast_tree.statements.iter().zip(out.statements.iter()) {
+            //     assert!(out, expected_out);
+        }
     }
 }