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use std::hash::Hash;
use super::SVMCell;

/// ForkTable
/// ---------
///
/// Contains an implementation of the `ForkTable` data structure for storing
/// scoped data.
#[cfg_attr(feature = "unstable",
    stable(feature = "forktable", since = "0.0.1") )]
pub mod forktable;

/// AST
/// ---
///
/// Contains a trait definition for an abstract syntax tree (AST) node.
/// Compilers targeting Seax should provide concrete implementations of this
/// trait for their AST node types. This ensures a consistant interface for
/// Seax compilers.
#[cfg_attr(feature = "unstable",
    stable(feature = "ast", since = "0.0.1") )]
pub mod ast;

// Reexports
pub use self::forktable::ForkTable;
pub use self::ast::ASTNode;

/// Represents an index into the Seax VM's environment stack.
///
/// Since the environment stack is a stack of stacks, an index is represented
/// by two unsigned integers. The first represents the level in the `$e`
/// stack,  and the second represents the index within the list at that level.
#[cfg_attr(feature = "unstable",
    stable(feature = "scope", since = "0.0.1") )]
pub type Index = (u64, u64);

/// The symbol table for bound names is represented as a
/// `ForkTable` mapping `&str` (names) to `(uint,uint)` tuples,
/// representing the location in the `$e` stack storing the value
/// bound to that name.
#[cfg_attr(feature = "unstable",
    stable(feature = "forktable", since = "0.0.1") )]
pub type SymTable<'a> = forktable::ForkTable<'a, &'a str, Index>;

/// A `CompileResult` is either `Ok(SVMCell)` or `Err(&str)`
#[cfg_attr(feature = "unstable",
    stable(feature = "compile", since = "0.0.1") )]
pub type CompileResult = Result<Vec<SVMCell>, String>;

/// Trait for a symbol table
#[cfg_attr(feature = "unstable",
    stable(feature = "scope", since = "0.0.1") )]
pub trait Scope<K>
where K: Eq + Hash {
    /// Bind a name to a scope.
    ///
    /// Returnsthe indices for that name in the SVM environment.
    #[cfg_attr(feature = "unstable",
        stable(feature = "scope", since = "0.0.1") )]
    fn bind(&mut self, name: K, lvl: u64) -> Index;
    /// Look up a name against a scope.
    ///
    /// Returns the indices for that name in the SVM environment,
    /// or None if that name is unbound.
    #[cfg_attr(feature = "unstable",
        stable(feature = "scope", since = "0.0.1") )]
    fn lookup(&self, name: &K)            -> Option<Index>;
}