parser: initial expression parsing logic

Signed-off-by: Amneesh Singh <natto@weirdnatto.in>

src/parser/entity.rs

@@ -9,6 +9,7 @@ use crate::lexer::{
 use std::rc::Rc;
 
 impl<'a> Parser<'a> {
+    /// entity ::= module | class | fn
     pub(super) fn parse_entity(&mut self) -> Option<Entity> {
         use TokenKeyword::*;
         let token = self.peek_token();
@@ -17,7 +18,7 @@ impl<'a> Parser<'a> {
             match keyword {
                 Module => Some(Entity::Module(self.parse_module()?)),
                 Class => Some(Entity::Class(self.parse_class()?)),
-                Fn => Some(Entity::Fn(self.parse_function()?)),
+                Fn => Some(Entity::Fn(self.parse_fn()?)),
                 _ => {
                     self.error_expected_peek("entity");
                     None
@@ -29,6 +30,7 @@ impl<'a> Parser<'a> {
         }
     }
 
+    /// module ::= "module" ident "{" { module | fn | static | class } "}"
     fn parse_module(&mut self) -> Option<Module> {
         self.next_token();
 
@@ -46,7 +48,7 @@ impl<'a> Parser<'a> {
             if let TokenKind::Keyword(keyword) = &self.peek_token().kind {
                 children.push(match keyword {
                     Module => ModuleChildren::Module(self.parse_module()?),
-                    Fn => ModuleChildren::Fn(self.parse_function()?),
+                    Fn => ModuleChildren::Fn(self.parse_fn()?),
                     Static => ModuleChildren::Static(self.parse_static()?),
                     Class => ModuleChildren::Class(self.parse_class()?),
                     _ => {
@@ -65,6 +67,7 @@ impl<'a> Parser<'a> {
         Some(Module { name, children })
     }
 
+    /// class ::= "class" ident "{" { fn | static | let } "}"
     fn parse_class(&mut self) -> Option<Class> {
         self.next_token();
 
@@ -81,7 +84,7 @@ impl<'a> Parser<'a> {
             self.trim_newlines();
             if let TokenKind::Keyword(keyword) = &self.peek_token().kind {
                 children.push(match keyword {
-                    Fn => ClassChildren::Fn(self.parse_function()?),
+                    Fn => ClassChildren::Fn(self.parse_fn()?),
                     Static => ClassChildren::Static(self.parse_static()?),
                     Let => ClassChildren::Let(self.parse_let()?),
                     _ => {
@@ -100,7 +103,9 @@ impl<'a> Parser<'a> {
         Some(Class { name, children })
     }
 
-    fn parse_function(&mut self) -> Option<Fn> {
+    /// fn ::= "fn" ident "(" [ identWithTy { "," identWithTy } ] ")" [ ":" ty ]
+    ///        "{" { statement } "}"
+    fn parse_fn(&mut self) -> Option<Fn> {
         self.next_token();
 
         let name = self.parse_ident()?;
@@ -115,7 +120,7 @@ impl<'a> Parser<'a> {
 
         loop {
             if self.peek_token().kind == TokenKind::Identifier {
-                params.push(self.parse_ident_with_type()?);
+                params.push(self.parse_ident_with_ty()?);
             }
 
             if !self.skip_token(TokenKind::Symbol(TokenSymbol::Comma)) {
@@ -164,16 +169,7 @@ fn test_parse_entity() {
                }
              }
 
-
-             fn fn02(): int {
-
-
-
-
-
-
-
-            }
+             fn fn02 (): int { }
           }"#,
     );
     assert_eq!(
@@ -190,7 +186,7 @@ fn test_parse_entity() {
                         children: vec![Statement::Static(Let {
                             name: "let01".into(),
                             ty: Ty::Int,
-                            expr: Some(Expr::Int(4))
+                            expr: Some(Expr::Literal(Literal::Int(4)))
                         })]
                     })]
                 }),

src/parser/expr.rs

@@ -1,109 +1,356 @@
 use super::Parser;
-use crate::ast::*;
+use crate::ast::{
+    self,
+    *,
+};
 use crate::lexer::{
+    TokenDelimiter,
     TokenKeyword,
     TokenKind,
     TokenLiteral,
     TokenSymbol,
 };
+use std::rc::Rc;
 
 impl<'a> Parser<'a> {
-    pub(super) fn parse_statement(&mut self) -> Option<Statement> {
-        use TokenKeyword::*;
-
-        match self.peek_token().kind {
-            TokenKind::Keyword(Static) => Some(Statement::Static(self.parse_static()?)),
-            TokenKind::Keyword(Let) => Some(Statement::Let(self.parse_let()?)),
-            _ => Some(Statement::Expr(self.parse_expr()?)),
-        }
-    }
-
-    pub(super) fn parse_static(&mut self) -> Option<Let> {
-        self.next_token();
-        if self.peek_token().kind != TokenKind::Keyword(TokenKeyword::Let) {
-            self.error_expected_peek("let");
-            return None;
-        }
-
-        self.parse_let()
-    }
-
-    pub(super) fn parse_let(&mut self) -> Option<Let> {
+    /// exprIf ::= "if" expr block [ else (block | exprIf ) ]
+    fn parse_expr_if(&mut self) -> Option<If> {
+        // skip "if"
         self.next_token();
 
-        let (name, ty) = self.parse_ident_with_type()?;
-        let expr;
+        let cond = Box::new(self.parse_expr()?);
+        let then = self.parse_expr_block()?;
 
-        if self.skip_token(TokenKind::Symbol(TokenSymbol::Eq)) {
-            expr = Some(self.parse_expr()?);
+        if !self.skip_token(TokenKind::Keyword(TokenKeyword::Else)) {
+            return Some(If {
+                cond,
+                then,
+                or: None,
+            });
+        }
+
+        if self.peek_token().kind != TokenKind::Keyword(TokenKeyword::If) {
+            return Some(If {
+                cond,
+                then,
+                or: Some(Box::new(ElseType::Else(self.parse_expr_block()?))),
+            });
+        }
+
+        Some(If {
+            cond,
+            then,
+            or: Some(Box::new(ElseType::If(self.parse_expr_if()?))),
+        })
+    }
+
+    /// exprBlock ::= "{" { statement } "}"
+    fn parse_expr_block(&mut self) -> Option<Vec<Statement>> {
+        let mut statements = vec![];
+
+        // skip {
+        self.next_token();
+
+        loop {
             self.trim_newlines();
-        } else if self.skip_token(TokenKind::Newline) {
-            expr = None;
-        } else {
-            self.error_expected_peek("= or newline");
+            if self.skip_token(TokenKind::Delimiter(TokenDelimiter::BraceClose)) {
+                break;
+            }
+            statements.push(self.parse_statement()?);
+        }
+
+        Some(statements)
+    }
+
+    /// exprLoop ::= "loop" exprBlock
+    fn parse_expr_loop(&mut self) -> Option<Vec<Statement>> {
+        self.next_token();
+        if self.peek_token().kind != TokenKind::Delimiter(TokenDelimiter::BraceOpen) {
+            self.error_expected_peek("{");
             return None;
         }
 
-        Some(Let { name, ty, expr })
+        self.parse_expr_block()
     }
 
-    fn parse_expr(&mut self) -> Option<Expr> {
+    /// exprAtom ::= ( "(" expr ")" ) | ident | int | float | char | exprBlock | exprLoop | exprIf
+    fn parse_expr_atom(&mut self) -> Option<Expr> {
+        use ast::Literal::*;
         use TokenKind::*;
 
-        match self.peek_token().kind {
-            Literal(TokenLiteral::Int) => Some(Expr::Int(self.parse_int()?)),
-            Literal(TokenLiteral::Float) => Some(Expr::Float(self.parse_float()?)),
-            Literal(TokenLiteral::Char) => Some(Expr::Char(self.parse_char()?)),
+        // TODO: check lvalue validity in the analysis phase
+        Some(match self.peek_token().kind {
+            Delimiter(TokenDelimiter::ParenOpen) => {
+                self.next_token(); // skip (
+
+                let expr = self.parse_expr()?;
+
+                if !self.skip_token(TokenKind::Delimiter(TokenDelimiter::ParenClose)) {
+                    self.error_expected_peek(")");
+                    return None;
+                }
+
+                expr
+            }
+            Identifier => {
+                let token = self.next_token();
+                Expr::Identifier(Rc::clone(&token.val))
+            }
+            Literal(TokenLiteral::Int) => Expr::Literal(Int(self.parse_int()?)),
+            Literal(TokenLiteral::Float) => Expr::Literal(Float(self.parse_float()?)),
+            Literal(TokenLiteral::Char) => Expr::Literal(Char(self.parse_char()?)),
+            Delimiter(TokenDelimiter::BraceOpen) => Expr::Block(self.parse_expr_block()?),
+            Keyword(TokenKeyword::Loop) => Expr::Loop(self.parse_expr_loop()?),
+            Keyword(TokenKeyword::If) => Expr::If(self.parse_expr_if()?),
             _ => {
                 self.error_expected_peek("expression");
-                None
+                return None;
             }
-        }
+        })
     }
-}
 
-#[test]
-fn test_parse_let() {
-    let mut parser = Parser::new(
-        r#"static let test01: int = 4
-           let test02: char = '6'
-           static let test03: float
-           let test04 = 9"#,
-    );
-    assert_eq!(
-        parser.parse_static(),
-        Some(Let {
-            name: "test01".into(),
-            ty: Ty::Int,
-            expr: Some(Expr::Int(4))
+    /// exprUnary ::= [ unaryOp ] exprAtom
+    /// unaryOp   ::= "+" | "-" | "~"
+    fn parse_expr_unary(&mut self) -> Option<Expr> {
+        use TokenSymbol::*;
+        Some(match self.peek_token().kind {
+            TokenKind::Symbol(symbol @ (Minus | Plus | Tilde)) => {
+                self.next_token();
+                Expr::Op(symbol, Box::new(self.parse_expr_atom()?), None)
+            }
+            _ => self.parse_expr_atom()?,
         })
-    );
-    assert_eq!(
-        parser.parse_let(),
-        Some(Let {
-            name: "test02".into(),
-            ty: Ty::Char,
-            expr: Some(Expr::Char('6'))
+    }
+
+    /// exprArithmeticMul ::= exprUnary [ arithmeticMulOp exprArithmeticMul ]
+    /// arithmeticMulOp   ::= "*" | "/" | "%"
+    fn parse_expr_arithmetic_mul(&mut self) -> Option<Expr> {
+        use TokenSymbol::*;
+        let lhs = self.parse_expr_unary()?;
+
+        Some(match self.peek_token().kind {
+            TokenKind::Symbol(symbol @ (Star | Slash | Percent)) => {
+                self.next_token();
+                Expr::Op(
+                    symbol,
+                    Box::new(lhs),
+                    Some(Box::new(self.parse_expr_arithmetic_mul()?)),
+                )
+            }
+            _ => lhs,
         })
-    );
-    assert_eq!(
-        parser.parse_static(),
-        Some(Let {
-            name: "test03".into(),
-            ty: Ty::Float,
-            expr: None
+    }
+
+    /// exprArithmeticAdd ::= exprArithmeticMul [ arithmeticAddOp exprArithmeticAdd ]
+    /// arithmeticAddOp   ::= "+" | "-"
+    fn parse_expr_arithmetic_add(&mut self) -> Option<Expr> {
+        use TokenSymbol::*;
+        let lhs = self.parse_expr_arithmetic_mul()?;
+
+        Some(match self.peek_token().kind {
+            TokenKind::Symbol(symbol @ (Plus | Minus)) => {
+                self.next_token();
+                Expr::Op(
+                    symbol,
+                    Box::new(lhs),
+                    Some(Box::new(self.parse_expr_arithmetic_add()?)),
+                )
+            }
+            _ => lhs,
         })
-    );
-    assert_eq!(parser.parse_let(), None);
+    }
+
+    /// exprBitwiseShift ::= exprArithmeticAdd [ bitwiseShiftOp exprBitwiseShift ]
+    /// bitwiseShiftOp   ::= "<<" | ">>"
+    fn parse_expr_bitwise_shift(&mut self) -> Option<Expr> {
+        use TokenSymbol::*;
+        let lhs = self.parse_expr_arithmetic_add()?;
+
+        Some(match self.peek_token().kind {
+            TokenKind::Symbol(symbol @ (Shl | Shr)) => {
+                self.next_token();
+                Expr::Op(
+                    symbol,
+                    Box::new(lhs),
+                    Some(Box::new(self.parse_expr_bitwise_shift()?)),
+                )
+            }
+            _ => lhs,
+        })
+    }
+
+    /// exprBitwiseAnd ::= exprBitwiseShift [ "&" exprBitwiseAnd ]
+    fn parse_expr_bitwise_and(&mut self) -> Option<Expr> {
+        let lhs = self.parse_expr_bitwise_shift()?;
+        let symbol = TokenSymbol::And;
+
+        if !self.skip_token(TokenKind::Symbol(symbol)) {
+            return Some(lhs);
+        }
+
+        Some(Expr::Op(
+            symbol,
+            Box::new(lhs),
+            Some(Box::new(self.parse_expr_bitwise_and()?)),
+        ))
+    }
+
+    /// exprBitwiseXor ::= exprBitwiseAnd [ "^" exprBitwiseXor ]
+    fn parse_expr_bitwise_xor(&mut self) -> Option<Expr> {
+        let lhs = self.parse_expr_bitwise_and()?;
+        let symbol = TokenSymbol::Caret;
+
+        if !self.skip_token(TokenKind::Symbol(symbol)) {
+            return Some(lhs);
+        }
+
+        Some(Expr::Op(
+            symbol,
+            Box::new(lhs),
+            Some(Box::new(self.parse_expr_bitwise_xor()?)),
+        ))
+    }
+
+    /// exprBiwiseOr ::= exprBitwiseXor [ "|" exprBitwiseOr ]
+    fn parse_expr_bitwise_or(&mut self) -> Option<Expr> {
+        let lhs = self.parse_expr_bitwise_xor()?;
+        let symbol = TokenSymbol::Or;
+
+        if !self.skip_token(TokenKind::Symbol(symbol)) {
+            return Some(lhs);
+        }
+
+        Some(Expr::Op(
+            symbol,
+            Box::new(lhs),
+            Some(Box::new(self.parse_expr_bitwise_or()?)),
+        ))
+    }
+
+    /// exprAssign   ::= exprBitwiseOr [ relationalOp exprRelational ]
+    /// relationalOp ::= ">" | "<" | ">=" | "<=" | "==" | "!="
+    fn parse_expr_relational(&mut self) -> Option<Expr> {
+        use TokenSymbol::*;
+        let lhs = self.parse_expr_bitwise_or()?;
+
+        Some(match self.peek_token().kind {
+            TokenKind::Symbol(symbol @ (Gt | Lt | GtEq | LtEq | EqEq | Ne)) => {
+                self.next_token();
+                Expr::Op(
+                    symbol,
+                    Box::new(lhs),
+                    Some(Box::new(self.parse_expr_relational()?)),
+                )
+            }
+            _ => lhs,
+        })
+    }
+
+    /// exprLogicalAnd ::= exprLogicalRelational [ "&&" exprLogicalAnd ]
+    fn parse_expr_logical_and(&mut self) -> Option<Expr> {
+        let lhs = self.parse_expr_relational()?;
+        let symbol = TokenSymbol::AndAnd;
+
+        if !self.skip_token(TokenKind::Symbol(symbol)) {
+            return Some(lhs);
+        }
+
+        Some(Expr::Op(
+            symbol,
+            Box::new(lhs),
+            Some(Box::new(self.parse_expr_logical_and()?)),
+        ))
+    }
+
+    /// exprLogicalOr ::= exprLogicalAnd [ "||" exprLogicalOr ]
+    fn parse_expr_logical_or(&mut self) -> Option<Expr> {
+        let lhs = self.parse_expr_logical_and()?;
+        let symbol = TokenSymbol::OrOr;
+
+        if !self.skip_token(TokenKind::Symbol(symbol)) {
+            return Some(lhs);
+        }
+
+        Some(Expr::Op(
+            symbol,
+            Box::new(lhs),
+            Some(Box::new(self.parse_expr_logical_or()?)),
+        ))
+    }
+
+    /// exprAssign ::= exprLogicalOr [ assignOp exprAssign ]
+    /// assignOp   ::= "=" | "+=" | "-=" | "*=" | "/=" | "%=" | "^=" | "<<=" | ">>=" | "&=" | "|="
+    fn parse_expr_assign(&mut self) -> Option<Expr> {
+        use TokenSymbol::*;
+        let lhs = self.parse_expr_logical_or()?;
+
+        Some(match self.peek_token().kind {
+            TokenKind::Symbol(
+                symbol @ (Eq | PlusEq | MinusEq | StarEq | SlashEq | PercentEq | CaretEq | ShlEq
+                | ShrEq | AndEq | OrEq),
+            ) => {
+                self.next_token();
+                Expr::Op(
+                    symbol,
+                    Box::new(lhs),
+                    Some(Box::new(self.parse_expr_assign()?)),
+                )
+            }
+            _ => lhs,
+        })
+    }
+
+    /// exprControl ::= "continue" | "break" | "return" [ exprControl ] | exprAssign
+    fn parse_expr_control(&mut self) -> Option<Expr> {
+        use TokenKeyword::*;
+
+        Some(match self.peek_token().kind {
+            TokenKind::Keyword(Continue) => {
+                self.next_token();
+                Expr::Continue
+            }
+            TokenKind::Keyword(Break) => {
+                self.next_token();
+                Expr::Break
+            }
+            TokenKind::Keyword(Return) => {
+                self.next_token();
+                Expr::Return(self.parse_expr_control().map(Box::new))
+            }
+            _ => self.parse_expr_assign()?,
+        })
+    }
+
+    /// entrypoint for expression parsing using recursive descent parsing
+    ///
+    /// <https://en.wikipedia.org/wiki/Recursive_descent_parser>
+    /// expr ::= exprControl
+    fn parse_expr(&mut self) -> Option<Expr> {
+        self.parse_expr_control()
+    }
+
+    pub(super) fn parse_expr_ln(&mut self) -> Option<Expr> {
+        let expr = self.parse_expr();
+        if !self.skip_token(TokenKind::Newline) {
+            self.error_expected_peek("newline");
+            return None;
+        }
+        expr
+    }
 }
 
 #[test]
 fn test_parse_expr_literals() {
+    use Literal::*;
+
     let mut parser = Parser::new("4524 3123.15e4 9e2 9083482.429455 'c' 3331.13.3");
-    assert_eq!(parser.parse_expr(), Some(Expr::Int(4524)));
-    assert_eq!(parser.parse_expr(), Some(Expr::Float(3123.15e4)));
-    assert_eq!(parser.parse_expr(), Some(Expr::Float(9e2)));
-    assert_eq!(parser.parse_expr(), Some(Expr::Float(9083482.429455)));
-    assert_eq!(parser.parse_expr(), Some(Expr::Char('c')));
+    assert_eq!(parser.parse_expr(), Some(Expr::Literal(Int(4524))));
+    assert_eq!(parser.parse_expr(), Some(Expr::Literal(Float(3123.15e4))));
+    assert_eq!(parser.parse_expr(), Some(Expr::Literal(Float(9e2))));
+    assert_eq!(
+        parser.parse_expr(),
+        Some(Expr::Literal(Float(9083482.429455)))
+    );
+    assert_eq!(parser.parse_expr(), Some(Expr::Literal(Char('c'))));
     assert_eq!(parser.parse_expr(), None);
 }

src/parser/literal.rs

@@ -1,10 +1,12 @@
 use super::Parser;
 use crate::lexer::{
     TokenKind,
+    TokenLiteral,
     TokenSymbol,
 };
 
 impl<'a> Parser<'a> {
+    /// int ::= digit { digit }
     pub(super) fn parse_int(&mut self) -> Option<i32> {
         let val = self.next_token().val;
         let mut integer: i32 = 0;
@@ -36,10 +38,13 @@ impl<'a> Parser<'a> {
                 }
             }
         }
+
         Some(integer)
     }
 
+    // didnt use parse() because i wanted to do this myself for some reason
     /// f32 can be NaN and inf as well
+    /// float ::= int [ "." { digit } ] [ "e" { digit } ]
     pub(super) fn parse_float(&mut self) -> Option<f32> {
         let token = self.next_token();
         let mut chars = token.val.chars();
@@ -68,6 +73,10 @@ impl<'a> Parser<'a> {
                         _ => s = 1,
                     }
 
+                    if self.peek_token().kind != TokenKind::Literal(TokenLiteral::Int) {
+                        break;
+                    }
+
                     exp = self.parse_int()? * s;
                     break;
                 }
@@ -93,6 +102,7 @@ impl<'a> Parser<'a> {
         Some(float)
     }
 
+    /// char ::= "'" letter "'"
     pub(super) fn parse_char(&mut self) -> Option<char> {
         // the lexer ensures that the 0th and 2nd characters are both '
         self.next_token().val.chars().nth(1)

src/parser/mod.rs

@@ -5,6 +5,7 @@
 mod entity;
 mod expr;
 mod literal;
+mod statement;
 
 use crate::ast::{
     Parent,
@@ -60,6 +61,7 @@ impl<'a> Parser<'a> {
         return self.lexer.peek_token();
     }
 
+    /// newline ::= "\n"
     fn trim_newlines(&mut self) {
         while self.peek_token().kind == TokenKind::Newline {
             self.next_token();
@@ -75,6 +77,7 @@ impl<'a> Parser<'a> {
         false
     }
 
+    /// ty ::= "int" | "float" | "char"
     fn parse_ty(&mut self) -> Option<Ty> {
         let ty: Ty;
 
@@ -96,6 +99,7 @@ impl<'a> Parser<'a> {
         Some(ty)
     }
 
+    /// ident ::= ( letter | "_" ) { letter | digit | "_" }
     fn parse_ident(&mut self) -> Option<Rc<str>> {
         if self.peek_token().kind != TokenKind::Identifier {
             self.error_expected_peek("identifier");
@@ -105,7 +109,8 @@ impl<'a> Parser<'a> {
         Some(Rc::clone(&self.next_token().val))
     }
 
-    fn parse_ident_with_type(&mut self) -> Option<(Rc<str>, Ty)> {
+    /// identWithTy ::= letter ":" ty
+    fn parse_ident_with_ty(&mut self) -> Option<(Rc<str>, Ty)> {
         let ident = self.parse_ident()?;
 
         if !self.skip_token(TokenKind::Symbol(TokenSymbol::Colon)) {
@@ -118,6 +123,7 @@ impl<'a> Parser<'a> {
 
     /// Returns an [`Entity`] vector after parsing
     ///
+    /// parent ::= { entity }
     /// [`Entity`]: crate::ast::Entity
     pub fn parse(&mut self) -> Option<Parent> {
         let mut parent = vec![];

src/parser/statement.rs

@@ -0,0 +1,87 @@
+use super::Parser;
+use crate::ast::*;
+use crate::lexer::{
+    TokenKeyword,
+    TokenKind,
+    TokenSymbol,
+};
+
+impl<'a> Parser<'a> {
+    /// statement ::= static | let | expr
+    pub(super) fn parse_statement(&mut self) -> Option<Statement> {
+        use TokenKeyword::*;
+
+        Some(match self.peek_token().kind {
+            TokenKind::Keyword(Static) => Statement::Static(self.parse_static()?),
+            TokenKind::Keyword(Let) => Statement::Let(self.parse_let()?),
+            _ => Statement::Expr(self.parse_expr_ln()?),
+        })
+    }
+
+    /// static ::="static" let
+    pub(super) fn parse_static(&mut self) -> Option<Let> {
+        self.next_token();
+
+        if self.peek_token().kind != TokenKind::Keyword(TokenKeyword::Let) {
+            self.error_expected_peek("let");
+            return None;
+        }
+
+        self.parse_let()
+    }
+
+    /// let ::= "let" identWithTy "=" expr
+    pub(super) fn parse_let(&mut self) -> Option<Let> {
+        self.next_token();
+
+        let (name, ty) = self.parse_ident_with_ty()?;
+
+        let expr = if self.skip_token(TokenKind::Symbol(TokenSymbol::Eq)) {
+            self.parse_expr_ln()
+        } else if self.skip_token(TokenKind::Newline) {
+            None
+        } else {
+            self.error_expected_peek("= or newline");
+            return None;
+        };
+
+        Some(Let { name, ty, expr })
+    }
+}
+
+#[test]
+fn test_parse_let() {
+    use Literal::*;
+
+    let mut parser = Parser::new(
+        r#"static let test01: int = 4
+           let test02: char = '6'
+           static let test03: float
+           let test04 = 9"#,
+    );
+    assert_eq!(
+        parser.parse_static(),
+        Some(Let {
+            name: "test01".into(),
+            ty: Ty::Int,
+            expr: Some(Expr::Literal(Int(4)))
+        })
+    );
+    assert_eq!(
+        parser.parse_let(),
+        Some(Let {
+            name: "test02".into(),
+            ty: Ty::Char,
+            expr: Some(Expr::Literal(Char('6')))
+        })
+    );
+    assert_eq!(
+        parser.parse_static(),
+        Some(Let {
+            name: "test03".into(),
+            ty: Ty::Float,
+            expr: None
+        })
+    );
+    assert_eq!(parser.parse_let(), None);
+}