goodbye eopl

beautiful-racket-lib/br/eopl.rkt

@@ -1,97 +0,0 @@
-#lang br
-(require racket/struct (for-syntax br/datum))
-(provide define-datatype cases occurs-free?)
-
-#;(begin
-    (struct lc-exp () #:transparent)
-    
-    (struct var-exp lc-exp (var) #:transparent
-      #:guard (λ(var name)
-                (unless (symbol? var)
-                  (error name (format "arg ~a not ~a" var 'symbol?)))
-                (values var)))
-    
-    (struct lambda-exp lc-exp (bound-var body) #:transparent
-      #:guard (λ(bound-var body name)
-                (unless (symbol? bound-var)
-                  (error name (format "arg ~a not ~a" bound-var 'symbol?)))
-                (unless (lc-exp? body)
-                  (error name (format "arg ~a not ~a" body 'lc-exp?)))
-                (values bound-var body)))
-    
-    (struct app-exp lc-exp (rator rand) #:transparent
-      #:guard (λ(rator rand name)
-                (unless (lc-exp? rator)
-                  (error name (format "arg ~a not ~a" rator 'lc-exp?)))
-                (unless (lc-exp? rand)
-                  (error name (format "arg ~a not ~a" rand 'lc-exp?)))
-                (values rator rand))))
-
-
-(define #'(define-datatype _base-type _base-type-predicate?
-            (_subtype [_field _field-predicate?] ...) ...)
-  #'(begin
-      (struct _base-type () #:transparent #:mutable)
-      (struct _subtype _base-type (_field ...) #:transparent #:mutable
-        #:guard (λ(_field ... name)
-                  (unless (_field-predicate? _field)
-                    (error name (format "arg ~a is not ~a" _field '_field-predicate?))) ...
-                  (values _field ...))) ...))
-
-
-(define-datatype lc-exp lc-exp?
-  (var-exp [var symbol?])
-  (lambda-exp [bound-var symbol?] [body lc-exp?])
-  (app-exp [rator lc-exp?] [rand lc-exp?]))
-
-
-#;(define (occurs-free? search-var exp)
-    (cond
-      [(var-exp? exp) (let ([var (var-exp-var exp)])
-                        (eqv? var  search-var))]
-      [(lambda-exp? exp) (let ([bound-var (lambda-exp-bound-var exp)]
-                               [body (lambda-exp-body exp)])
-                           (and (not (eqv? search-var bound-var))
-                                (occurs-free? search-var body)))]
-      [(app-exp? exp) (let ([rator (app-exp-rator exp)]
-                            [rand (app-exp-rand exp)])
-                        (or
-                         (occurs-free? search-var rator)
-                         (occurs-free? search-var rand)))]))
-
-(define-syntax (cases stx)
-  (syntax-case stx (else)
-    [(_ _base-type _input-var
-        [_subtype (_positional-var ...) . _body] ...
-        [else . _else-body])
-     (inject-syntax ([#'(_subtype? ...) (suffix-id #'(_subtype ...) "?")])
-                    #'(cond
-                        [(_subtype? _input-var) (match-let ([(list _positional-var ...) (struct->list _input-var)])
-                                                    . _body)] ...
-                                                                 [else . _else-body]))]
-    [(_ _base-type _input-var
-        _subtype-case ...)
-     #'(cases _base-type _input-var
-         _subtype-case ...
-         [else (void)])]))
-
-
-(define (occurs-free? search-var exp)
-  (cases lc-exp exp
-    [var-exp (var) (eqv? var search-var)]
-    [lambda-exp (bound-var body)
-                (and (not (eqv? search-var bound-var))
-                     (occurs-free? search-var body))]
-    [app-exp (rator rand)
-             (or
-              (occurs-free? search-var rator)
-              (occurs-free? search-var rand))]))
-
-
-(module+ test
-  (require rackunit)
-  (check-true (occurs-free? 'foo (var-exp 'foo)))
-  (check-false (occurs-free? 'foo (var-exp 'bar)))
-  (check-false (occurs-free? 'foo (lambda-exp 'foo (var-exp 'bar))))
-  (check-true (occurs-free? 'foo (lambda-exp 'bar (var-exp 'foo))))
-  (check-true (occurs-free? 'foo (lambda-exp 'bar (lambda-exp 'zim (lambda-exp 'zam (var-exp 'foo)))))))