pub mod util;
pub mod display;
pub mod check;
pub mod subst;


use crate::sexp::SExp;


#[derive(Clone,Debug,PartialEq)]
pub enum Type {

    Integer,

    Arrow(Box<Type>, Box<Type>),

    List(Vec<Type>),

    /// Type for generics
    /// and also error messages
    /// with unknown types
    VarType(String),

}


#[derive(Debug,PartialEq)]
pub enum TypeError {

    UndefinedVariable(String),

    UnboundGeneric(String),

    InvalidOperator {
	operator: SExp,
	expected: Type,
	found:    Type,
    },

    InvalidArgList {
	arglist:  SExp,
	expected: Type,
	found:    Type,
    },

    OtherError
}


impl Type {
    /// Tests if the type has no variable types.
    ///
    /// **Examples**
    /// ```rust
    /// use melisp::r#type::{*, Type::*, TypeError::*, util::*};
    ///
    /// assert!(Integer.is_concrete());
    /// assert!(!VarType("a".to_string()).is_concrete());
    ///
    /// assert!(arr(Integer, Integer).is_concrete());
    /// assert!(!arr(VarType("b".to_string()), Integer).is_concrete());
    ///
    /// assert!(
    ///     List(vec![Integer, Integer, arr(Integer, Integer)]).is_concrete()
    /// );
    /// assert!(
    ///     !List(vec![Integer, VarType("a".to_string()), Integer])
    ///         .is_concrete()
    /// );
    /// ```
    pub fn is_concrete(&self) -> bool {
        todo!()
    }
}