"Stream protocol words are rarely called directly, since code which only works with one stream at a time should be written use " { $link "stdio" } " instead, wrapping I/O operations such as " { $link read } " and " { $link write } " in a " { $link with-stream } ". This leads more simpler, more reusable and more robust code."
"Most I/O code only operates on one stream at a time. The " { $emphasis "default stream" } " is an implicit parameter used by many I/O words designed for this particular use-case. Using this idiom improves code in three ways:"
{ $list
{ "Code becomes simpler because there is no need to keep a stream around on the stack." }
{ "Code becomes more robust because " { $link with-stream } " automatically closes the stream if there is an error." }
{ "Code becomes more reusable because it can be written to not worry about which stream is being used, and instead the caller can use " { $link with-stream } " to specify the source or destination for I/O operations." }
}
"For example, here is a program which reads the first line of a file, converts it to an integer, then reads that many characters, and splits them into groups of 16:"
"dup stream-readln number>string over stream-read 16 group"
"swap dispose"
}
"This code has two problems: it has some unnecessary stack shuffling, and if either " { $link stream-readln } " or " { $link stream-read } " throws an I/O error, the stream is not closed because " { $link dispose } " is never reached. So we can add a call to " { $link with-disposal } " to ensure the stream is always closed:"
" dup stream-readln number>string over stream-read"
" 16 group"
"] with-disposal"
}
"This code is robust however it is more complex than it needs to be since. This is where the default stream words come in; using them, the above can be rewritten as follows:"
"Unless rebound in a child namespace, this variable will be set to a console stream for interacting with the user."
{ $subsection read1 }
{ $subsection read }
{ $subsection read-until }
{ $subsection readln }
{ $subsection flush }
{ $subsection write1 }
{ $subsection write }
{ $subsection print }
{ $subsection nl }
{ $subsection bl }
"Formatted output:"
{ $subsection format }
{ $subsection write-object }
{ $subsection with-style }
{ $subsection with-nesting }
"Tabular output:"
{ $subsection tabular-output }
{ $subsection with-row }
{ $subsection with-cell }
{ $subsection write-cell }
"A pair of combinators support rebinding the " { $link stdio } " variable:"
{ $subsection with-stream }
{ $subsection with-stream* } ;
ARTICLE: "stream-utils""Stream utilities"
"There are a few useful stream-related words which are not generic, but merely built up from the stream protocol."
$nl
"First, a simple composition of " { $link stream-write } " and " { $link stream-nl } ":"
{ $subsection stream-print }
"Sluring an entire stream into memory all at once:"
{ $subsection lines }
{ $subsection contents }
"Copying the contents of one stream to another:"
{ $subsection stream-copy } ;
ARTICLE: "streams""Streams"
"Input and output centers on the concept of a " { $emphasis "stream" } ", which is a source or sink of characters. Streams also support formatted output, which may be used to present styled text in a manner independent of output medium."
{ $values { "seps"string } { "stream""an input stream" } { "str/f""a string or " { $link f } } { "sep/f""a character or " { $link f } } }
{ $contract "Reads characters from the stream, until the first occurrence of a separator character, or stream exhaustion. In the former case, the separator character is pushed on the stack, and is not part of the output string. In the latter case, the entire stream contents are output, along with " { $link f } "." }
{ $contract "Writes a character of output to the stream. If the stream does buffering, output may not be performed immediately; use " { $link stream-flush } " to force output." }
{ $contract "Writes a string of output to the stream. If the stream does buffering, output may not be performed immediately; use " { $link stream-flush } " to force output." }
{ $contract "Waits for any pending output to complete." }
{ $notes "With many output streams, written output is buffered and not sent to the underlying resource until either the buffer is full, or this word is called." }
{ $contract "Writes a line terminator. If the stream does buffering, output may not be performed immediately; use " { $link stream-flush } " to force output." }
{ $contract "Writes formatted text to the stream. If the stream does buffering, output may not be performed immediately; use " { $link stream-flush } " to force output."
$nl
"The " { $snippet "style" } " hashtable holds character style information. See " { $link "character-styles" } "." }
{ $description "Copies the contents of one stream into another, closing both streams when done." }
$io-error ;
HELP:stdio
{ $var-description "Holds a stream, used for various implicit stream operations. Rebound using " { $link with-stream } " and " { $link with-stream* } "." } ;
{ $description "Reads " { $snippet "n" } " characters of input from the " { $link stdio } " stream. Outputs a truncated string or " { $link f } " on stream exhaustion." }
{ $values { "seps"string } { "str/f""a string or " { $link f } } { "sep/f""a character or " { $link f } } }
{ $contract "Reads characters from the " { $link stdio } " stream. until the first occurrence of a separator character, or stream exhaustion. In the former case, the separator character is pushed on the stack, and is not part of the output string. In the latter case, the entire stream contents are output, along with " { $link f } "." }
$io-error ;
HELP:write1
{ $values { "ch""a character" } }
{ $contract "Writes a character of output to the " { $link stdio } " stream. If the stream does buffering, output may not be performed immediately; use " { $link flush } " to force output." }
{ $description "Writes a string of output to the " { $link stdio } " stream. If the stream does buffering, output may not be performed immediately; use " { $link flush } " to force output." }
{ $description "Writes a line terminator to the " { $link stdio } " stream. If the stream does buffering, output may not be performed immediately; use " { $link flush } " to force output." }
{ $description "Writes formatted text to the " { $link stdio } " stream. If the stream does buffering, output may not be performed immediately; use " { $link flush } " to force output." }
{ $description "Calls the quotation in a new dynamic scope with the " { $link stdio } " stream rebound to a nested paragraph stream, with formatting information applied." }
{ $description "Calls a quotation which emits a series of equal-length table rows using " { $link with-row } ". The results are laid out in a tabular fashion on the " { $link stdio } " stream."
$nl
"The " { $snippet "style" } " hashtable holds table style information. See " { $link "table-styles" } "." }
{ $examples
{ $code
"{ { 1 2 } { 3 4 } }"
"H{ { table-gap { 10 10 } } } ["
" [ [ [ [ . ] with-cell ] each ] with-row ] each"
"] tabular-output"
}
}
$io-error ;
HELP:with-row
{ $values { "quot" quotation } }
{ $description "Calls a quotation which emits a series of table cells using " { $link with-cell } ". This word can only be called inside the quotation given to " { $link tabular-output } "." }
$io-error ;
HELP:with-cell
{ $values { "quot" quotation } }
{ $description "Calls a quotation in a new scope with the " { $link stdio } " stream rebound. Output performed by the quotation is displayed in a table cell. This word can only be called inside the quotation given to " { $link with-row } "." }
$io-error ;
HELP:write-cell
{ $values { "str"string } }
{ $description "Outputs a table cell containing a single string. This word can only be called inside the quotation given to " { $link with-row } "." }
{ $description "Calls the quotation in a new dynamic scope where calls to " { $link write } ", " { $link format } " and other stream output words automatically inherit style settings from " { $snippet "style" } "." }
{ $notes "Details are in the documentation for " { $link make-span-stream } "." }
$io-error ;
HELP:print
{ $values { "string"string } }
{ $description "Writes a newline-terminated string to the " { $link stdio } " stream." }
{ $description "Calls the quotation in a new dynamic scope, with the " { $link stdio } " variable rebound to " { $snippet "stream" } ". The stream is closed if the quotation returns or throws an error." } ;
{ $description "Calls the quotation in a new dynamic scope, with the " { $link stdio } " variable rebound to " { $snippet "stream" } "." }
{ $notes "This word does not close the stream. Compare with " { $link with-stream } "." } ;
HELP:bl
{ $description "Outputs a space character (" { $snippet "\" \"" } ")." }
$io-error ;
HELP:write-object
{ $values { "str"string } { "obj""an object" } }
{ $description "Writes a string to the " { $link stdio } " stream, associating it with the object. If formatted output is supported, the string will become a clickable presentation of the object, otherwise this word behaves like a call to " { $link write } "." }
