Rolling context buffer for backward context

[yoavnir]

Used similar to WRITE:

• CTXBUF + numeric constant indicating count of backwards lines
• DUMPCTX - causes an emptying of the buffer
• SETCTR + numeric constant indicating count of forward lines
• settablectr() function - decremented with each line. Starts at zero and decreases with every line

Example:

# Print 3 lines before and 5 lines after any line that contains 'marker'
1-* 1
if "includes(@@,'marker')" then
    DUMPCTX # dumps the queue
    SETCTR   5
endif
if "settablectr()<=0" then
    CTXBUF  3  # eats the record into a size-3 queue. Otherwise it gets printed
endif

[yoavnir]

I don't like the names. This needs some more thought.

[yoavnir]

How about:

• a new CONTEXT keyword that can be used in several ways:
  • CONTEXT ON causes the writes to go to a rotating buffer.
  • CONTEXT OFF causes the writes to go to the output.
  • CONTEXT DUMP 3,7 causes the previous 3 lines and following 7 lines to go to output. The rest of the rotating context buffer is cleared.
  • CONTEXT PREFIX expression - causes a line containing the result of the evaluated expression to be printed before the context dump
  • CONTEXT SUFFIX expression - causes a line containing the result of the evaluated expression to be printed after the context dump

[yoavnir]

Thinking it over, how about making it more like the REDO keyword, in the sense that specs units following it deal with a different buffer.

So CONTEXT n would mean that we're now dealing with a previous line. Example:

# Print 3 lines before and 5 lines after any line that contains 'marker'
# Yes, this assumes the buffer doesn't include another marker
if "includes(@@,'marker')" then
    CONTEXT -3 1-* 1 WRITE
    CONTEXT -2 1-* 1 WRITE
    CONTEXT -1 1-* 1 WRITE
    CONTEXT 0  1-* 1 WRITE
    CONTEXT 1  1-* 1 WRITE
    CONTEXT 2  1-* 1 WRITE
    CONTEXT 3  1-* 1 WRITE
    CONTEXT 4  1-* 1 WRITE
    CONTEXT 5  1-* 1
endif