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@risgk risgk/arith_big.rb
Last active Dec 17, 2015

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TAPL 演習3.5.17 Rubyでの実装例
# TYPES AND PROGRAMMING LANGUAGES by Benjamin C. Pierce Copyright (c)2002 Benjamin C. Pierce
# Excercise 3.5.17
class Array
def isnumericval
t = self
case
when t[0] == :zero
true
when t[0] == :succ
t[1].isnumericval
else
false
end
end
def isval
t = self
case
when t[0] == :true
true
when t[0] == :false
true
when t.isnumericval
true
else
false
end
end
def eval
t = self
case
when t.isval
t
when t[0] == :if && t[1].eval == [:true] && t[2].eval.isval
t[2].eval
when t[0] == :if && t[1].eval == [:false] && t[3].eval.isval
t[3].eval
when t[0] == :succ && t[1].eval.isnumericval
[:succ,t[1].eval]
when t[0] == :pred && t[1].eval == [:zero]
[:zero]
when t[0] == :pred && t[1].eval[0] == :succ && t[1].eval[1].isnumericval
t[1].eval[1]
when t[0] == :iszero && t[1].eval == [:zero]
[:true]
when t[0] == :iszero && t[1].eval[0] == :succ && t[1].eval[1].isnumericval
[:false]
else
t
end
end
end
# Test
printf("test1: %s\n", [:true].eval == [:true])
printf("test2: %s\n", [:false].eval == [:false])
printf("test3: %s\n", [:if,[:true],[:true],[:false]].eval == [:true])
printf("test4: %s\n", [:if,[:false],[:true],[:false]].eval == [:false])
printf("test5: %s\n", [:if,[:if,[:true],[:true],[:false]],[:true],[:false]].eval == [:true])
printf("test6: %s\n", [:if,[:if,[:false],[:true],[:false]],[:true],[:false]].eval == [:false])
printf("test7: %s\n", [:zero].eval == [:zero])
printf("test8: %s\n", [:succ,[:pred,[:zero]]].eval == [:succ,[:zero]])
printf("test9: %s\n", [:iszero,[:succ,[:zero]]].eval == [:false])
printf("test10: %s\n", [:iszero,[:pred,[:succ,[:zero]]]].eval == [:true])
printf("test11: %s\n", [:iszero,[:pred,[:succ,[:succ,[:zero]]]]].eval == [:false])
printf("test12: %s\n", [:iszero,[:true]].eval == [:iszero,[:true]])
printf("test13: %s\n", [:succ,[:true]].eval == [:succ,[:true]])
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