add a new example, and replace example/Abort.rtero with example/trail.retro (thanks to kiyoshi)

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crc 2019-12-30 15:05:42 +00:00
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3 changed files with 102 additions and 52 deletions

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There are people who consider `abort` to be the most
fundamental building block in writing programs. For
them, it is not just a debugging tool.
~~~
:s:shout (s-) '!_ s:prepend s:put nl 'Stack_:_ s:put dump-stack nl ;
{{
'Depth var
:message (-) 'abort_with_trail_invoked s:shout nl
'Do__reset__to_clear_stack. s:put nl ;
:put-name (a-) fetch d:lookup-xt
dup n:-zero? [ d:name s:put nl ] [ drop ] choose ;
---reveal---
:trail repeat pop put-name again ;
:abort (-?) depth !Depth message trail ;
:s:abort (s-) 's:abort_:_ s:prepend s:put nl abort ;
}}
~~~
`trail` leaves garbage on the stack.
This garbage is difficult to shake off since `trail`
destroys the contents of the return stack. The easiest
way I have found so far is to `reset` manually.
To test, run the following code interactively:
```
:a 'aaa s:abort ;
:b a ;
:c b ;
c
reset
```
## assert
~~~
:assert (q-) call [ abort ] -if ;
:assert.verbous (q-) call [ 'assert_:_fail s:abort ] -if ;
~~~
If `0;` is invoked with an empty stack, it fails and
kills the session.
```
:t 'before_ s:put 0; 'after s:put nl ;
'#0_t_nl_#1_t_nl s:evaluate
'reset_t s:evaluate (--_kills_session
```
If this is dangerous, place an assertion before `0;` .

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This is a small thing to calculate the potential impact of ice cap melt
on the global sea level.
~~~
:ice:ANTARTIC .26.54 .1000000 f:* ; (from_the_bedrock2_survey
:ice:GREENLAND .2900000 ; (from_web.viu.ca/earle/geol305
:ice:total ice:ANTARTIC ice:GREENLAND f:+ ;
:ice:rise<mm> ice:total .361 f:/ ;
:ice:rise<m> ice:rise<mm> .1000 f:/ ;
:ice:rise<m,adj> ice:rise<m> .0.91 f:* ;
ice:total 'Total_volume_(km^3):_ s:put f:put nl
ice:rise<mm> 'Rise_(mm):___________ s:put f:put nl
ice:rise<m> 'Rise_(m):____________ s:put f:put nl nl
ice:rise<m,adj> 'Rise_(m,_adjusted_for_density):_ s:put f:put nl
~~~
Output:
Total volume (km^3): 29440000.000000
Rise (mm): 81551.246537
Rise (m): 81.551247
Rise (m, adjusted for density): 74.211634
Sources:
- bedrock2 survey: https://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf
- greenland ice: https://web.viu.ca/earle/geol305/The%20Greenland%20Ice%20Sheet.pdf
- sea level rise: https://www.realworldvisuals.com/blog-1/could-rocks-cause-sea-levels-to-rise

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Some consider abort to be the most fundamental building block
in writing programs. `trail` and `listen` abort execution.
~~~
:s:shout (s-) '!!->_ s:prepend '_<-!! s:append s:put nl ;
{{
:put-name (a-) fetch d:lookup-xt
dup n:-zero? [ d:name s:put nl ] &drop choose ;
---reveal---
:trail (-0) '1_or_more_0s_left_on_the_stack s:shout
repeat pop put-name again ;
}}
~~~
`trail` adds at least one 0 ( FALSE flag ) on top of stack.
```
:t0 trail ;
:t1 t0 ;
:t2 t1 ;
t2
```
Example of `0;` killing a session:
```
:t 'before_ s:put 0; 'after s:put nl ;
#0 t (works
#1 t (works
reset t (kills_session
```
If this is dangerous, place a `guard` or a `check` before `0;` .
~~~
:d:ego (-s) d:last d:name compile:lit ; immediate
:s:prepend;put s:prepend s:put nl ;
:s:trail (s-0) '(_s:trail_)__ s:prepend;put trail ;
:s:listen (s-) '(_s:listen_)__ s:prepend;put listen ;
:guard (q-) call &trail -if ;
:check (q-) call &listen -if ;
:s:guard (sq-) call &drop &s:trail choose ;
:s:check (sq-) call &drop &s:listen choose ;
~~~
`check` is less noisy than `trail` .
```
:t0 (q-) 'Doing... s:put nl
d:ego '_charlie s:append swap s:guard
'Next... s:put nl ;
:u0 t0 ;
:v0 d:ego '_calling_u0 s:append s:put;nl u0 ;
nl nl
&TRUE v0 nl
&FALSE v0 nl
```
```
:t1 (q-) 'Doing... s:put nl
d:ego '_ckpt s:append swap s:check
'Next... s:put nl ;
:u1 t1 ;
:v1 d:ego '_calling_u1 s:append s:put;nl u1 ;
nl nl
&TRUE v1 nl
&FALSE v1 nl
```