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62 lines
1.9 KiB
Racket
62 lines
1.9 KiB
Racket
9 years ago
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#lang br
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(provide #%top-interaction) ; activates the REPL
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;; reader goes first and
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;; 1) converts surface syntax into Rackety expressions (wrapping in `(inst ...)`)
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;; 2) creates a module specifying semantics source (in this case, same module)
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(provide read-syntax)
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(define (read-syntax src-path src-input-port)
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(define inst-datums (for/list ([src-line (in-lines src-input-port)]
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#:when (regexp-match #px"\\w" src-line))
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(format-datum '(inst ~a) src-line)))
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(syntax-let ([#'(inst-stx ...) inst-datums]) ; ok to bind with non-syntax
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#'(module stack-lang-module "stack.rkt"
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inst-stx ...)))
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(define stack empty)
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;; semantics always start with #%module-begin, which unwraps the content of the module and rewraps it
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(provide (rename-out [stack-module-begin #%module-begin]))
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(define #'(stack-module-begin instructions ...)
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#'(#%module-begin
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instructions ...
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(first stack)))
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;; then file is processed like a normal Racket file.
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(provide inst)
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(define (inst . args)
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(if (<= 1 (length args) 2)
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(let ([proc (first args)])
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(apply proc (cdr args)))
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(void)))
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(provide push)
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(define (push arg)
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(display "push: ")
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(cond
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[(procedure? arg)
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(displayln (format "got ~a, replacing ~a and ~a with result" arg (first stack) (second stack) ))
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(set! stack (cons (arg (first stack) (second stack)) (cddr stack)))]
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[else (displayln (format "storing value ~a" arg))
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(set! stack (cons arg stack))])
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(displayln stack))
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;; exercises
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(provide pop)
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(define (pop)
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(display "pop: ")
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(displayln (format "got ~a" (car stack)))
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(set! stack (cdr stack))
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(displayln stack))
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(provide swap)
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(define (swap)
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(display "swap: ")
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(displayln (format "~a and ~a" (first stack) (second stack)))
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(set! stack (list* (second stack) (first stack) (cddr stack)))
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(displayln stack))
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