parser: parse let statements

- TODO: Type expressions
token: Add `mut` keyword

libconlang/src/parser.rs

@@ -359,7 +359,15 @@ impl Parser {
     fn stmt(&mut self) -> PResult<Stmt> {
         let token = self.peek()?;
         match token.ty() {
-            Type::Keyword(Keyword::Let) => todo!("Let statements"),
+            Type::Keyword(Keyword::Let) => Ok(Stmt::Let {
+                mutable: self.consume().keyword(Keyword::Mut).is_ok(),
+                name: self.identifier()?,
+                ty: self
+                    .consume_type(Type::Colon)
+                    .and_then(Self::identifier)
+                    .ok(),
+                init: self.consume_type(Type::Eq).and_then(Self::expr).ok(),
+            }),
             _ => {
                 let out = Stmt::Expr(self.expr()?);
                 self.consume_type(Type::Semi)?;

libconlang/src/token/token_type.rs

@@ -83,6 +83,7 @@ pub enum Keyword {
     If,
     In,
     Let,
+    Mut,
     Return,
     True,
     While,
@@ -167,6 +168,7 @@ impl Display for Keyword {
             Self::If => "if".fmt(f),
             Self::In => "in".fmt(f),
             Self::Let => "let".fmt(f),
+            Self::Mut => "mut".fmt(f),
             Self::Return => "return".fmt(f),
             Self::True => "true".fmt(f),
             Self::While => "while".fmt(f),
@@ -187,6 +189,7 @@ impl FromStr for Keyword {
             "if" => Self::If,
             "in" => Self::In,
             "let" => Self::Let,
+            "mut" => Self::Mut,
             "return" => Self::Return,
             "true" => Self::True,
             "while" => Self::While,