e0/src/parser.lalrpop

use crate::ast::*;

grammar;

pub Program: Vec<Decl<()>> = Decl* => <>;

Decl: Decl<()> = {
  Func => Decl::Func(<>),
};

Func: Func<()> = {
  "fn" <name:Ident> "(" <args:Args> ")" "->" <return_ty:Type> "{" <stmts:Stmt*> "}" =>
    Func { name, args, return_ty, stmts, ty: (), },
};

Args: Vec<Arg> = Punct<",", Arg>? => <>.unwrap_or_else(|| Vec::new());

Arg: Arg = <name:Ident> ":" <ty:Type> => Arg { name, ty };

Stmt: Stmt<()> = {
  "let" <name:Ident> <ty:ColonType?> "=" <expr:Expr> ";" =>
    Stmt::Let(name, ty, expr),
  "return" <expr:Expr?> ";" => Stmt::Return(expr),
  IfElse => Stmt::IfElse(<>),
};

ColonType: Type = ":" <ty:Type> => ty;

IfElse: IfElse<()> =
  "if" <cond:Expr> "{" <body:Stmt*> "}" <else_clause:Else?> =>
    IfElse { cond, body, else_clause };

Else: ElseClause<()> = "else" <else_clause:Else_> => else_clause;
Else_: ElseClause<()> = {
  IfElse => ElseClause::If(Box::new(<>)),
  "{" <body:Stmt*> "}" => ElseClause::Body(body),
};

Expr: Expr<()> = {
  #[precedence(level = "0")]
  "(" <expr:Expr> ")" => expr,

  #[precedence(level = "0")]
  r"[0-9]+" => Expr { kind: ExprKind::Int(<>.parse::<i64>().unwrap()), ty: () },

  #[precedence(level = "0")]
  Ident => Expr { kind: ExprKind::Var(<>), ty: () },

  #[precedence(level = "2")]
  <func:Ident> "(" <args:Punct<",", Expr>?> ")" =>
    Expr { kind: ExprKind::Call(func, args.unwrap_or_else(|| vec![])), ty: () },

  #[precedence(level = "8")]
  #[assoc(side = "left")]
  <left:Expr> <op:AddOp> <right:Expr> => Expr {
    kind: ExprKind::BinOp(Box::new(left), op, Box::new(right)),
    ty: (),
  },

  #[precedence(level = "13")]
  #[assoc(side = "none")]
  <left:Expr> <op:CompareOp> <right:Expr> => Expr {
    kind: ExprKind::BinOp(Box::new(left), op, Box::new(right)),
    ty: (),
  },
};

AddOp: Op = {
  "+" => Op::Plus,
};

CompareOp: Op = {
  "<" => Op::LessThan,
  ">" => Op::GreaterThan,
};

Type: Type = {
  "int" => Type::Int,
};

Ident: String = r"([A-Za-z][A-Za-z0-9_]*)|(_[A-Za-z0-9_]+)" => <>.to_string();

Punct<P, T>: Vec<T> = {
  P => vec![],
  <first:T> <rest:(P Punct<P, T>)?> => {
    match rest {
      Some(rest) => {
        let (_, mut vec) = rest;
        vec.insert(0, first);
        vec
      }
      None => vec![first],
    }
  },
};