3.5. kink/CONTROL¶
The mod which provides various control funs.
3.5.1. CONTROL.try($body $on_returned $on_raised)¶
`try` traps an exception raised by an invocation of $body.
Preconditions:
• $body must be a thunk fun
• $on_returned must be a fun which takes an argument, which is the result of $body
• $on_raised must be a fun which takes an exception raised in the invocation of $body
`try` invokes $body with no args.
If the invocation of $body terminates without raising an exception, `try` tail-calls $on_returned with the result of the invocation of $body.
If the invocation of $body terminates raising an exception, `try` tail-calls $on_raised with the exception.
Example:
:TRACE.require_from('kink/')
:CONTROL.require_from('kink/')
:attempt_divide_10_by <- {(:Divisor)
CONTROL.try(
{ 10 // Divisor }
{(:Result)
stdout.print_line('result: {}'.format(Result))
}
{(:Exc)
Exc.desc_iter.each{(:Line)
stdout.print_line(Line)
}
}
)
}
attempt_divide_10_by(2)
# Output:
# result: 5
attempt_divide_10_by(0)
# Output:
# exception traces: from oldest to newest
# [startup]
# [builtin:kink-mods/kink/_startup/STARTUP.kn L236 C3 _startup_aux] -->_startup_aux(Args Dep)
# [builtin:kink-mods/kink/_startup/STARTUP.kn L219 C11 try] CONTROL.-->try(
# [builtin:kink-mods/kink/CONTROL.kn L204 C19 reset] :handler = KONT.-->reset('kink/CONTROL-try'){
# [builtin:kink-mods/kink/CONTROL.kn L205 C10 body] :R = -->body
# [builtin:kink-mods/kink/_startup/STARTUP.kn L221 C7 _start] -->_start(Non_opts Dep)
# [builtin:kink-mods/kink/_startup/STARTUP.kn L122 C3 if] -->if(Non_opts.empty?
# [builtin:kink-mods/kink/_startup/STARTUP.kn L135 C7 branch] -->branch(
# [builtin:kink-mods/kink/_startup/STARTUP.kn L160 C11 _run_script] -->_run_script($script_fun Script_args)
# [builtin:kink-mods/kink/_startup/STARTUP.kn L113 C3 script_fun] -->script_fun(Binding)
# [(stdin) L22 C1 attempt_divide_10_by] -->attempt_divide_10_by(0)
# [(stdin) L5 C11 try] CONTROL.-->try(
# [builtin:kink-mods/kink/CONTROL.kn L204 C19 reset] :handler = KONT.-->reset('kink/CONTROL-try'){
# [builtin:kink-mods/kink/CONTROL.kn L205 C10 body] :R = -->body
# [(stdin) L6 C10 op_intdiv] { 10 -->// Divisor }
# exception message: Num.op_intdiv: zero division: 10 is divided by 0
3.5.2. CONTROL.while($cond $body)¶
CONTROL.while calls $body repeatedly while $cond returns true.
Preconditions:
• $cond must be a thunk fun which returns a bool
• $body must be a thunk fun
CONTROL.while first calls $cond with no args. If $cond returns true, CONTROL.while calls $body with no args. It repeats until Fun returns false.
Example:
:CONTROL.require_from('kink/')
:Vec <- [1 2 3]
CONTROL.while{ ! Vec.empty? }{
:N = Vec.pop_front
stdout.print_line(N.repr)
}
# Output:
# 1
# 2
# 3
3.5.3. CONTROL.with_finally($body)¶
`with_finally` provides functionality of resource releases at the end of the procedure which uses the resources.
`with_finally` calls $body with a fun, and returns the result of $body. Let $finally be the arg passed to $body.
Preconditions of $finally:
• $finally must be called within the corresponding invocation of $body.
• $finally takes a thunk.
When $finally is called with a thunk, the thunk is ensured to be called after the invocation of $body ends in the following ways:
(1) When the invocation of $body returns a val,
(2) When the invocation of $body is terminated by $break fun of CONTROL.with_break with a val, or
(3) When the invocation of $body raises an exception.
Example:
:CONTROL.require_from('kink/')
:CHARSET.require_from('kink/charset/')
:FILE.require_from('kink/io/')
:Text <- CONTROL.with_finally{(:finally)
:In = FILE.open_to_read('/path/to/file')
finally{ In.close }
CHARSET.utf8.bin_to_str(In.read_all)
}
stdout.print(Text) # prints the text in /path/to/file
In the example above, `In` is closed when exiting from `with_finally`, no matter whether `read_all` raises an exception or not.
$finally can be called multiple times. If $finally is called with thunks `T1`, `T2`, ,,, `Tn` respectively in that order, the thunks are called at the end of the invocation of $body in the order `Tn` ,,, `T2`, `T1`.
Example:
:CONTROL.require_from('kink/')
CONTROL.with_finally{(:finally)
finally{ stdout.print_line('T1') }
finally{ stdout.print_line('T2') }
finally{ stdout.print_line('T3') }
}
# Output:
# T3
# T2
# T1
TODO: elaborate on exception/jump handling.
3.5.4. CONTROL.with_break($body)¶
`with_break` provides functionality of parameterized non local exit.
`with_break` calls $body with a fun. Let $break be the fun.
Precondition of $break:
• $break takes an arbitrary argument.
• $break must be called within the corresponding invocation of $body.
When $break is called, it escapes from the corresponding invocation of `with_break`, and `with_break` returns the argument passed to $break.
If $break is not called within the invocation of `with_break`, `with_break` returns the result of $body.
Example:
:CONTROL.require_from('kink/')
:to_fizz_buzz <- {(:Num)
CONTROL.with_break{(:break)
if(Num % 15 == 0){ break('fizzbuzz') }
if(Num % 3 == 0){ break('fizz') }
if(Num % 5 == 0){ break('buzz') }
Num.show
}
}
1.up.take(20)
.map{(:N) to_fizz_buzz(N) }
.each{(:S) stdout.print(S + ' ') }
# => 1 2 fizz 4 buzz fizz 7 8 fizz buzz 11 fizz 13 14 fizzbuzz 16 17 fizz 19 buzz