56 lines
1.1 KiB
Text
56 lines
1.1 KiB
Text
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;; call/cc 的型別: (forall (A B C) in Any) (-> (-> (-> A C) B) (U A B))
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;; 異常處理 call/cc
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https://csl.name/post/lambda-macros-continuations/
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(define-library (try-catch)
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(import (scheme base)
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(print))
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(export
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try)
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(begin
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(define-syntax try
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(syntax-rules (catch)
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((try
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(exception-handler handler)
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body ...
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(catch exception-catcher))
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(begin
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(define handler (lambda (error) #f)) ; default: do nothing
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(call/cc
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(lambda (exit)
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(set! handler
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(lambda (error)
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(exception-catcher error)
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(exit)))
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body ...))))))))
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Example usage:
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(import (scheme base)
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(print)
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(try-catch))
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(println "--start--")
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(try
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(exception-handler oops)
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(define (divide a b)
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(if (zero? b)
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(oops "Division by zero")
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(println a "/" b " = " (inexact (/ a b)))))
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(divide 10 2)
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(divide 1 3)
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(divide 3 0)
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(println "This should not execute")
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(catch
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(lambda (error)
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(println "Hey, we caught an error: " error))))
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(println "--end--")
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