57 lines
2.1 KiB
Scheme
57 lines
2.1 KiB
Scheme
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;;; Copyright (C) Peter McGoron 2024
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;;; This program is free software: you can redistribute it and/or modify
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;;; it under the terms of the GNU General Public License as published by
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;;; the Free Software Foundation, version 3 of the License.
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;;;
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;;; This program is distributed in the hope that it will be useful,
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;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;;; GNU General Public License for more details.
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;;;
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;;; You should have received a copy of the GNU General Public License
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;;; along with this program. If not, see <https://www.gnu.org/licenses/>.
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;;;
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;;;
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;;; Handles messages passed to objects. The state of each object is
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;;; expected to be in the table or in the environment. Each message
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;;; invokes a procedure whose name is the first argument to the object,
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;;; and the arguments to that procedure are the rest of the arguments to
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;;; the object.
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;;; Lookup NAME-AS-SYMBOL in TABLE and returns the handler, or the default
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;;; handler if not available.
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(define object:lookup
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(lambda (table name-as-symbol)
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(let ((node (smap:search table (symbol->string name-as-symbol))))
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(if (null? node)
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(set! node (smap:search table "default")))
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(if (null? node)
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(error "object:lookup" "no handler found for" name-as-symbol)
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(map:val node)))))
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;;; Create an object with TABLE as its procedure table.
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(define object/table
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(lambda (table)
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(lambda (op . args)
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(apply (object:lookup table op) args))))
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;;; Append procedures to a table.
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(define object:append-table
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(lambda (table next-pairs)
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(if (null? next-pairs)
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table
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(let ((key (symbol->string (car next-pairs)))
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(proc (cadr next-pairs)))
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(object:append-table
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(car (smap:insert table key proc))
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(cddr next-pairs))))))
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;;; Convert a list of 'SYMBOL PROCEDURE ... into a table.
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(define object:list->table
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(lambda pairs
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(object:append-table '() pairs)))
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(define object/procedures
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(lambda procedures
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(object/table (apply object:list->table procedures))))
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