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\backslash
exerc1[10]
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Explain why short,
 simple examples of coroutines are hard for the author of a textbook to find.
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answer 
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Coroutines appear when there are several parts of the program coordinating among them,
 where each part performs a higher level task.
 While simple coroutines appear in higher level languages such as Python (in the form of generators),
 in languages such as assembly where they is no builtin support for them,
 they are more complex and slower than equivalent code that doesn't use coroutines,
 so their utility is not evident from these simple cases.
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\backslash
rexerc2[20]
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The program in the text starts up the 
\family typewriter
OUT
\family default
 coroutine first.
 What would happen if 
\family typewriter
IN
\family default
 were the first to be executed—
that is,
 if line 60 where changed from `
\family typewriter
JMP OUT1
\family default
' to `
\family typewriter
JMP IN1
\family default
'?
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answer 
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The first parsed character would be ignored,
 since the 
\family typewriter
OUT
\family default
 coroutine doesn't expect a character to be loaded already when it begins.
 Here 
\family typewriter
IN
\family default
 acts effectively like a generator for 
\family typewriter
OUT
\family default
.
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\backslash
rexerc6[22]
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Give coroutine linkage analogous to (1) for the case of 
\emph on
three
\emph default
 coroutines,
 
\family typewriter
A
\family default
,
 
\family typewriter
B
\family default
,
 and 
\family typewriter
C
\family default
,
 each of which can jump to either of the other two.
 (Whenever a coroutine is activated,
 it begins where it last left off.)
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answer 
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In principle,
 this would require us to extend the code to 
\emph on
six
\emph default
 coroutine linkages,
 like below:
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{
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BTOA  STJ  BX
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      JMP  AX
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CTOA  STJ  CX
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AX    JMP  A1
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ATOB  STJ  AX
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We can then elide the code for jumps that never happen.
 When the number of coroutines is large,
 typically each one only communicates with the next or they communicate with a central,
 coordinating coroutine that decides which to call next based on some protocol (maybe coroutines store the index of the next coroutine to run in some register,
 or coroutines are polled in order based on which has input data available,
 for example.)
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