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- #lang eopl
- ;******************************************************************************************
- ;;;;; Interpretador para lenguaje con condicionales, ligadura local y procedimientos
- ;; La definición BNF para las expresiones del lenguaje:
- ;;
- ;; <program> ::= <expression>
- ;; <a-program (exp)>
- ;; <expression> ::= <number>
- ;; <lit-exp (datum)>
- ;; ::= <identifier>
- ;; <var-exp (id)>
- ;; ::= <primitive> ({<expression>}*(,))
- ;; <primapp-exp (prim rands)>
- ;; ::= if <expresion> then <expresion> else <expression>
- ;; <if-exp (exp1 exp2 exp23)>
- ;; ::= let {identifier = <expression>}* in <expression>
- ;; <let-exp (ids rands body)>
- ;; ::= proc({<identificador>}*(,)) <expression>
- ;; <proc-exp (ids body)>
- ;; ::= (<expression> {<expression>}*)
- ;; <app-exp proc rands>
- ;; <primitive> ::= + | - | * | add1 | sub1
- ;******************************************************************************************
- ;******************************************************************************************
- ;Especificación Léxica
- (define scanner-spec-simple-interpreter
- '((white-sp
- (whitespace) skip)
- (comment
- ("%" (arbno (not #\newline))) skip)
- (identifier
- (letter (arbno (or letter digit "?"))) symbol)
- (number
- (digit (arbno digit)) number)
- (number
- ("-" digit (arbno digit)) number)))
- ;Especificación Sintáctica (gramática)
- (define grammar-simple-interpreter
- '((program (expression) a-program)
- (expression (number) lit-exp)
- (expression (identifier) var-exp)
- (expression
- (primitive "(" (separated-list expression ",")")")
- primapp-exp)
- (expression ("if" expression "then" expression "else" expression)
- if-exp)
- (expression ("let" (arbno identifier "=" expression) "in" expression)
- let-exp)
- ; características adicionales
- (expression ("proc" "(" (separated-list identifier ",") ")" expression)
- proc-exp)
- (expression ( "(" expression (arbno expression) ")")
- app-exp)
- ;;;;;;
- (primitive ("+") add-prim)
- (primitive ("-") substract-prim)
- (primitive ("*") mult-prim)
- (primitive ("add1") incr-prim)
- (primitive ("sub1") decr-prim)))
- ;Tipos de datos para la sintaxis abstracta de la gramática
- ;Construidos manualmente:
- ;(define-datatype program program?
- ; (a-program
- ; (exp expression?)))
- ;
- ;(define-datatype expression expression?
- ; (lit-exp
- ; (datum number?))
- ; (var-exp
- ; (id symbol?))
- ; (primapp-exp
- ; (prim primitive?)
- ; (rands (list-of expression?)))
- ; (if-exp
- ; (test-exp expression?)
- ; (true-exp expression?)
- ; (false-exp expression?))
- ; (let-exp
- ; (ids (list-of symbol?))
- ; (rans (list-of expression?))
- ; (body expression?))
- ; (proc-exp
- ; (ids (list-of symbol?))
- ; (body expression?))
- ; (app-exp
- ; (proc expression?)
- ; (args (list-of expression?))))
- ;
- ;(define-datatype primitive primitive?
- ; (add-prim)
- ; (substract-prim)
- ; (mult-prim)
- ; (incr-prim)
- ; (decr-prim))
- ;Construidos automáticamente:
- (sllgen:make-define-datatypes scanner-spec-simple-interpreter grammar-simple-interpreter)
- (define show-the-datatypes
- (lambda () (sllgen:list-define-datatypes scanner-spec-simple-interpreter grammar-simple-interpreter)))
- ;*******************************************************************************************
- ;Parser, Scanner, Interfaz
- ;El FrontEnd (Análisis léxico (scanner) y sintáctico (parser) integrados)
- (define scan&parse
- (sllgen:make-string-parser scanner-spec-simple-interpreter grammar-simple-interpreter))
- ;El Analizador Léxico (Scanner)
- (define just-scan
- (sllgen:make-string-scanner scanner-spec-simple-interpreter grammar-simple-interpreter))
- ;El Interpretador (FrontEnd + Evaluación + señal para lectura )
- (define interpretador
- (sllgen:make-rep-loop "--> "
- (lambda (pgm) (eval-program pgm))
- (sllgen:make-stream-parser
- scanner-spec-simple-interpreter
- grammar-simple-interpreter)))
- ;*******************************************************************************************
- ;El Interprete
- ;eval-program: <programa> -> numero
- ; función que evalúa un programa teniendo en cuenta un ambiente dado (se inicializa dentro del programa)
- (define eval-program
- (lambda (pgm)
- (cases program pgm
- (a-program (body)
- (eval-expression body (init-env))))))
- ; Ambiente inicial
- ;(define init-env
- ; (lambda ()
- ; (extend-env
- ; '(x y z)
- ; '(4 2 5)
- ; (empty-env))))
- (define init-env
- (lambda ()
- (extend-env
- '(x y)
- (list 4 2) (empty-env))))
- ;eval-expression: <expression> <enviroment> -> numero
- ; evalua la expresión en el ambiente de entrada
- (define eval-expression
- (lambda (exp env)
- (cases expression exp
- (lit-exp (datum) datum)
- (var-exp (id) (apply-env env id))
- (primapp-exp (prim rands)
- (let ((args (eval-rands rands env)))
- (apply-primitive prim args)))
- (if-exp (test-exp true-exp false-exp)
- (if (true-value? (eval-expression test-exp env))
- (eval-expression true-exp env)
- (eval-expression false-exp env)))
- (let-exp (ids rands body)
- (let ((args (eval-rands rands env)))
- (eval-expression body
- (extend-env ids args env))))
- (proc-exp (ids body)
- (closure ids body env))
- (app-exp (rator rands)
- (let ((proc (eval-expression rator env))
- (args (eval-rands rands env)))
- (if (procval? proc)
- (apply-procedure proc args)
- (eopl:error 'eval-expression
- "Attempt to apply non-procedure ~s" proc)))))))
- ; funciones auxiliares para aplicar eval-expression a cada elemento de una
- ; lista de operandos (expresiones)
- (define eval-rands
- (lambda (rands env)
- (map (lambda (x) (eval-rand x env)) rands)))
- (define eval-rand
- (lambda (rand env)
- (eval-expression rand env)))
- ;apply-primitive: <primitiva> <list-of-expression> -> numero
- (define apply-primitive
- (lambda (prim args)
- (cases primitive prim
- (add-prim () (+ (car args) (cadr args)))
- (substract-prim () (- (car args) (cadr args)))
- (mult-prim () (* (car args) (cadr args)))
- (incr-prim () (+ (car args) 1))
- (decr-prim () (- (car args) 1)))))
- ;true-value?: determina si un valor dado corresponde a un valor booleano falso o verdadero
- (define true-value?
- (lambda (x)
- (not (zero? x))))
- ;*******************************************************************************************
- ;Procedimientos
- (define-datatype procval procval?
- (closure
- (ids (list-of symbol?))
- (body expression?)
- (env environment?)))
- ;apply-procedure: evalua el cuerpo de un procedimientos en el ambiente extendido correspondiente
- (define apply-procedure
- (lambda (proc args)
- (cases procval proc
- (closure (ids body env)
- (eval-expression body (extend-env ids args env))))))
- ;*******************************************************************************************
- ;Ambientes
- ;definición del tipo de dato ambiente
- (define-datatype environment environment?
- (empty-env-record)
- (extended-env-record (syms (list-of symbol?))
- (vals (list-of scheme-value?))
- (env environment?)))
- (define scheme-value? (lambda (v) #t))
- ;empty-env: -> enviroment
- ;función que crea un ambiente vacío
- (define empty-env
- (lambda ()
- (empty-env-record))) ;llamado al constructor de ambiente vacío
- ;extend-env: <list-of symbols> <list-of numbers> enviroment -> enviroment
- ;función que crea un ambiente extendido
- (define extend-env
- (lambda (syms vals env)
- (extended-env-record syms vals env)))
- ;función que busca un símbolo en un ambiente
- (define apply-env
- (lambda (env sym)
- (cases environment env
- (empty-env-record ()
- (eopl:error 'apply-env "No binding for ~s" sym))
- (extended-env-record (syms vals env)
- (let ((pos (list-find-position sym syms)))
- (if (number? pos)
- (list-ref vals pos)
- (apply-env env sym)))))))
- ;****************************************************************************************
- ;Funciones Auxiliares
- ; funciones auxiliares para encontrar la posición de un símbolo
- ; en la lista de símbolos de unambiente
- (define list-find-position
- (lambda (sym los)
- (list-index (lambda (sym1) (eqv? sym1 sym)) los)))
- (define list-index
- (lambda (pred ls)
- (cond
- ((null? ls) #f)
- ((pred (car ls)) 0)
- (else (let ((list-index-r (list-index pred (cdr ls))))
- (if (number? list-index-r)
- (+ list-index-r 1)
- #f))))))
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