guile/step5_tco.scm

   1 ;;  Copyright (C) 2015
   2 ;;      "Mu Lei" known as "NalaGinrut" <NalaGinrut@gmail.com>
   3 ;;  This file is free software: you can redistribute it and/or modify
   4 ;;  it under the terms of the GNU General Public License as published by
   5 ;;  the Free Software Foundation, either version 3 of the License, or
   6 ;;  (at your option) any later version.
   7
   8 ;;  This file is distributed in the hope that it will be useful,
   9 ;;  but WITHOUT ANY WARRANTY; without even the implied warranty of
  10 ;;  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11 ;;  GNU General Public License for more details.
  12
  13 ;;  You should have received a copy of the GNU General Public License
  14 ;;  along with this program.  If not, see <http://www.gnu.org/licenses/>.
  15
  16 (import (readline) (reader) (printer) (ice-9 match) (srfi srfi-43)
  17         (srfi srfi-1) (ice-9 receive) (env) (core) (types))
  18
  19 (define *toplevel*
  20   (receive (b e) (unzip2 core.ns)
  21     (make-Env #:binds b #:exprs e)))
  22
  23 (define (READ)
  24   (read_str (readline "user> ")))
  25
  26 (define (eval_ast ast env)
  27   (define (_eval x) (EVAL x env))
  28   (match ast
  29     ((? _nil? obj) obj)
  30     ((? symbol? sym)
  31      (or ((env 'get) sym)
  32          ;; delay eval is good design here
  33          (lambda _ (throw 'mal-error (format #f "'~a' not found" sym)))))
  34     ((? list? lst) (map _eval lst))
  35     ((? vector? vec) (vector-map (lambda (i x) (_eval x)) vec))
  36     ((? hash-table? ht)
  37      (hash-for-each (lambda (k v) (hash-set! ht k (_eval v))) ht)
  38      ht)
  39     (else ast)))
  40
  41 (define (eval_func ast env)
  42   (define expr (eval_ast ast env))
  43   (match expr
  44     (((? procedure? proc) args ...)
  45      (apply proc args))
  46     (else 'mal-error (format #f "'~a' is not a valid form to apply!" expr))))
  47
  48 (define (eval_seq ast env)
  49   (cond
  50    ((null? ast) nil)
  51    ((null? (cdr ast)) (EVAL (car ast) env))
  52    (else
  53     (EVAL (car ast) env)
  54     (eval_seq (cdr ast) env))))
  55
  56 (define (EVAL ast env)
  57   (define (->list kvs) ((if (vector? kvs) vector->list identity) kvs))
  58   (define (%unzip2 kvs)
  59     (let lp((next kvs) (k '()) (v '()))
  60       (cond
  61        ;; NOTE: reverse is very important here!
  62        ((null? next) (values (reverse k) (reverse v)))
  63        ((null? (cdr next)) (throw 'mal-error "let*: Invalid binding form" kvs))
  64        (else (lp (cddr next) (cons (car next) k) (cons (cadr next) v))))))
  65   ;; NOTE: I wish I can use (while #t ...) for that, but this is not Lispy, which means
  66   ;;       it'll bring some trouble in control flow. We have to use continuations to return
  67   ;;       and use non-standard `break' feature. In a word, not elegant at all.
  68   ;;       The named let loop is natural for Scheme, but it looks a bit cheating. But NO!
  69   ;;       Such kind of loop is actually `while loop' in Scheme, I don't take advantage of
  70   ;;       TCO in Scheme to implement TCO, but it's the same principle with normal loop.
  71   ;;       If you're Lispy enough, there's no recursive at all while you saw named let loop.
  72   (let tco-loop((ast ast) (env env))
  73     (match ast
  74       (('def! k v) ((env 'set) k (EVAL v env)))
  75       (('let* kvs body)
  76        (let* ((new-env (make-Env #:outer env))
  77               (setter (lambda (k v) ((new-env 'set) k (EVAL v new-env)))))
  78          (receive (keys vals) (%unzip2 (->list kvs))
  79                   (for-each setter keys vals))
  80          (tco-loop body new-env)))
  81        (('do rest ...)
  82         (cond
  83          ((null? rest) (throw 'mal-error "do: Invalid form!" rest))
  84          ((= 1 (length rest)) (tco-loop (car rest) env))
  85          (else
  86           (let ((mexpr (take rest (1- (length rest))))
  87                 (tail-call (car (take-right rest 1))))
  88             (eval_seq mexpr env)
  89             (tco-loop tail-call env)))))
  90        (('if cnd thn els ...)
  91         (cond
  92          ((and (not (null? els)) (not (null? (cdr els))))
  93           ;; Invalid `if' form
  94           (throw 'mal-error "if: failed to match any pattern in form " ast))
  95          ((cond-true? (EVAL cnd env)) (tco-loop thn env))
  96          (else (if (null? els) nil (tco-loop (car els) env)))))
  97        (('fn* params body ...) ; function definition
  98         (lambda args
  99           (let ((nenv (make-Env #:outer env #:binds (->list params) #:exprs args)))
 100             (cond
 101              ((null? body) (throw 'mal-error "fn*: bad lambda in form " ast))
 102              ((= 1 (length body)) (tco-loop (car body) nenv))
 103              (else
 104               (let ((mexpr (take body (1- (length body))))
 105                     (tail-call (car (take-right body 1))))
 106                 (eval_seq mexpr nenv)
 107                 (tco-loop tail-call nenv)))))))
 108        ((? list?) (eval_func ast env)) ; function calling
 109        (else (eval_ast ast env)))))
 110
 111 (define (PRINT exp)
 112   (and (not (eof-object? exp))
 113        ;;(add-history str)
 114        (format #t "~a~%" (pr_str exp #t))))
 115
 116 (define (LOOP continue?)
 117   (and continue? (REPL)))
 118
 119 (define (REPL)
 120   (LOOP
 121    (catch 'mal-error
 122           (lambda () (PRINT (EVAL (READ) *toplevel*)))
 123           (lambda (k . e)
 124             (format #t "Error: ~a~%" (car e))))))
 125
 126 ;; NOTE: we have to reduce stack size to pass step5 test
 127 ((@ (system vm vm) call-with-stack-overflow-handler)
 128  1024
 129  (lambda () (REPL))
 130  (lambda k (throw 'mal-error "stack overflow")))
 131