diff options
| -rw-r--r-- | txr.1 | 97 |
1 files changed, 92 insertions, 5 deletions
@@ -44550,9 +44550,10 @@ If a negative indentation results, it is clamped to zero. The .code width-check function examines the state of the stream, taking into consideration -the current printing column position, the indentation state, and -indentation amount. It makes a decision either to introduce a line -break by printing a newline character, or else to print the +the current printing column position, the indentation state, +the indentation amount and an internal "force break" flag. It makes a decision +either to introduce a line break by printing a newline character, or else to +print the .meta alt-char character. @@ -44562,8 +44563,94 @@ is .codn nil , then the function has no effect at all. -The return value is always -.codn t . +The return value is +.code t +if the function has issued a line break, otherwise +.codn nil . + +.coNP Function @ force-break +.synb +.mets (force-break << stream ) +.syne +.desc +If the +.code force-break +function is called on a stream, it sets an internal "force break" flag which +affects the future behavior of +.codn width-check . +The +.code width-check +function examines this flag. If the flag is set, +.code width-check +clears it, and issues a line break without considering any other +conditions. + +The +.metn stream 's +.code force-break +flag is also cleared whenever a newline character is output. + +The +.code force-break +function returns +.codn stream . + +Note: the +.code force-break +is involved in line breaking decisions. Whenever a list or list-like syntax is +being printed, whenever an element of that syntax is broken into multiple +lines, a break is forced after that element, in order to avoid output +which resembles the following diagonally-creeping pattern: + +.cblk + (a b c (d e f + g h i) j (k l + m n) o) +.cble + +but instead is rendered in a more horizontally compact pattern: + +.cblk + (a b c (d e f + g h i) + j (k l + m n) + o) +.cble + +When the printer prints +.code "(d e f g h i)" +it uses the +.code width-check +function between the elements; that function issues the +break between the +.code f +and +.codn g . +The printer monitors the return value of +.codn width-check ; +it knows that since one of the calls returned +.codn t , +the object had been broken into two or more lines. It then calls +.code force-break +after printing the last element +.code i +of that object. Then, due to the force flag, the outer recursion of the +printer which is printing +.code "(a b c ...)" +will experience a break when it calls +.code width-check +before printing +.codn j . + +Custom +.code print +methods defined on structure objects can take advantage of +.code width-check +and +.code force-break +in the same way so that application-defined output integrates +with the formatting algorithm. .SS* Coprocesses .coNP Functions @ open-command and @ open-process |