40 lines
1.2 KiB
Scheme
40 lines
1.2 KiB
Scheme
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; Copyright (c) 1993-1999 by Richard Kelsey and Jonathan Rees. See file COPYING.
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; Provides input and output channels.
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(define (input-channel? thing)
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(and (channel? thing)
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(or (= (channel-status thing)
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(enum channel-status-option input))
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(= (channel-status thing)
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(enum channel-status-option special-input)))))
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(define (output-channel? thing)
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(and (channel? thing)
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(or (= (channel-status thing)
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(enum channel-status-option output))
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(= (channel-status thing)
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(enum channel-status-option special-output)))))
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(define (open-input-channel filename)
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(let ((channel (open-channel filename (enum channel-status-option input))))
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(if (channel? channel)
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channel
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(error "cannot open input file" filename))))
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(define (open-output-channel filename)
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(let ((channel (open-channel filename (enum channel-status-option output))))
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(if (channel? channel)
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channel
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(error "cannot open output file" filename))))
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(define (close-input-channel channel)
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(if (input-channel? channel)
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(close-channel channel)
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(call-error close-input-channel channel)))
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(define (close-output-channel channel)
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(if (output-channel? channel)
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(close-channel channel)
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(call-error close-output-channel channel)))
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