47 lines
1.7 KiB
Plaintext
47 lines
1.7 KiB
Plaintext
;;;; The dev-build break loop — spec-conditions.md §2.
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;;;;
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;;;; An unhandled error used to kill the program. Here it stops instead, on the
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;;;; frame that erred with nothing unwound, and waits for someone to pick a
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;;;; restart. Two of them, and the run takes a different one each time, so a
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;;;; break loop that always resumed the same way could not pass.
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(import agent "vendor:agent")
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(defstruct Missing [id i32])
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(defn fetch [n i32] i32
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(restart-case
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(do (error (Missing {.id n})) 0)
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(use-placeholder [] :report "Answer -1 for the missing value" -1)
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(retry [] 7)))
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;;; Two frames offering the same name, which §4 says resolves to the inner one
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;;; and only ever the inner one. The outer clause is therefore on every list a
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;;; break loop prints and reachable from no name at all, which is why a restart
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;;; is taken by *index* now. 900 is the proof: it is the only value in this
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;;; file that by-name lookup cannot produce.
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(defn shadowed [n i32] i32
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(restart-case
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(+ (restart-case (do (error (Missing {.id n})) 0)
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(retry [] 5))
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100)
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(retry [] 900)))
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(defstruct Other [])
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;;; A handler-case establishes a restart of its own, under a name nobody wrote,
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;;; and a break loop inside it must not offer that one: it is reached through
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;;; the form's handler, which carries the condition in. Only [keep] is listed.
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(defn caught [n i32] i32
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(restart-case
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(handler-case (do (error (Missing {.id n})) 0)
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[(Other [_o] 5)])
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(keep [] :report "Answer 42" 42)))
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(defn main [] i32
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(agent/start "/tmp/flan-break.sock")
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(print (fetch 1)) (println "")
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(print (fetch 2)) (println "")
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(print (shadowed 3)) (println "")
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(print (caught 4)) (println "")
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0)
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