export class Env
    (outer = null, data = {}) ->
        @outer = outer
        @data = data

    set: (symbol, ast) ->
        @data[symbol] = ast

    find: (symbol) ->
        if symbol of @data then @
        else if @outer? then @outer.find symbol

    get: (symbol) ->
        result = @try-get symbol
        if not result
        then throw new Error "'#{symbol}' not found"
        else result

    try-get: (symbol) ->
        env = @find symbol
        if env then env.data[symbol]