119 lines
4.0 KiB
Plaintext
119 lines
4.0 KiB
Plaintext
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The _readline_ collection (not to be confused with MzScheme's
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`read-line' procedure) provides glue for using GNU's readline library
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with the MzScheme read-eval-print-loop.
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Normal use of readline
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----------------------
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The _rep.ss_ library installs a readline-based input port, and hooks
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the prompt-and-read part of MzScheme's read-eval-print loop to
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interact with it.
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You can put the following in your ~/.mzschemerc so that MzScheme
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starts with readline support on xterms:
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(when (equal? "xterm" (getenv "TERM"))
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(dynamic-require '(lib "rep.ss" "readline") #f))
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or start MzScheme with
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mzscheme -L rep.ss readline
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The readline history is stored across invocations in MzScheme's
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preferences file, assuming MzScheme exits normally.
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Interacting with the readline-enabled input port
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------------------------------------------------
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The _pread.ss_ library provides customization, and support for
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prompt-reading after "rep.ss" installs the new input port.
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The reading facility that the new input port provides can be
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customized with these parameters:
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> currnet-prompt
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The prompt that is used, as a byte string. Defaults to #"> ".
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> show-all-prompts
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If #f, no prompt is shown until you write input that is completely
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readable. For example, when you type
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(foo bar) (+ 1
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2)
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you will see a single prompt in the beginning.
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The problem is that the first expression can be `(read-line)' which
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normally consumes the rest of the text on the *same* line. The
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default value of this parameter is therefore #t, making it mimic
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plain I/O interactions.
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> max-history
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The number of history entries to save. Defaults to 100.
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> keep-duplicates
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If this is #f (the default), then lines that are equal to the
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previous one are not added as new history items.
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> keep-blanks
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If #f (the default), blank input lines are not kept in history.
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The new input port that you get when you require "rep.ss" is a custom
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port that uses readline for all inputs. The problem is when you want
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to display a prompt and then read some input: readline will get
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confused if it's not used when the cursor is at the beginning of the
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line, which is why it has a `prompt' argument. To use this prompt:
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(parameterize ([readline-prompt some-byte-string])
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...code-that-reads...)
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This will make the first call to readline use the prompt, and
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subsequent calls will use an all-spaces prompt of the same length
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(this can happen if you're reading an s-expression). The normal value
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of `readline-prompt' is #f for an empty prompt (and 'spaces after the
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prompt is used, which is why you should use `parameterize' to restore
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it to #f).
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(A proper solution would be to install a custom output port too which
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will keep track of text that is displayed without a trailing newline.)
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Direct bindings for readline hackers
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------------------------------------
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The _readline.ss_ library provides two functions:
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> (readline prompt-string)
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prints the given prompt string and reads a line
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> (readline-bytes prompt-bytes)
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same as above, but using raw byte-strings for the prompt and
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returning a byte string
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> (add-history s)
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adds the given string to the readline history, which is accessible
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to the user via the up-arrow key
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> (add-history-bytes s)
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adds the given byte string to the readline history, which is
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accessible to the user via the up-arrow key
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> (set-completion-function! proc [type])
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sets readline's `rl_completion_entry_function' function according to
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proc, which is expected to be a `string -> (list-of string)'
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procedure; the `type' argument defaults to `_string' but you can use
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it with `_bytes' instead
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License Issues
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--------------
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GNU's readline library is covered by the GPL, and that applies to code
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that links with it. PLT Scheme is LGPL, so this code is not used by
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default -- you should explicitly enable it if you want to. Also, be
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aware that if you write code that uses this library, it will make your
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code link to the readline library when invoked -- with the usual GPL
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implications.
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