#lang typed-scheme

(require scheme/match)

;; First order language + interpreter.

(define-struct: Let (variable expression body))

(define-struct: Plus (a b))

;; (define (bind variable expression env)
;;   (cons (cons variable expression) env))

;; ;; eval
;; (define (interpret expression environment)
;;   (match expression
;;          ((struct Let (var exp body))
;;           (interpret body
;;                      (bind var
;;                            (interpret exp environment)  ;; strict
;;                            environment)))
;;          ((struct Plus (a b)) (+ a b))
;;          (else expression))) ;; self-eval

;; apply
;; (define (invoke fn