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43 lines
1.2 KiB
Plaintext
43 lines
1.2 KiB
Plaintext
=====================================================================
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Side effects in Nim
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=====================================================================
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Note: Side effects are implicit produced values! Maybe they should be
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explicit like in Haskell?
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The idea is that side effects and partial evaluation belong together:
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Iff a proc is side effect free and all its argument are evaluable at
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compile time, it can be evaluated by the compiler. However, really
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difficult is the ``newString`` proc: If it is simply wrapped, it
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should not be evaluated at compile time! On other occasions it can
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and should be evaluated:
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```nim
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proc toUpper(s: string): string =
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result = newString(len(s))
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for i in 0..len(s) - 1:
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result[i] = toUpper(s[i])
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```
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No, it really can always be evaluated. The code generator should transform
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``s = "\0\0\0..."`` back into ``s = newString(...)``.
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``new`` cannot be evaluated at compile time either.
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Raise statement
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===============
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It is impractical to consider ``raise`` as a statement with side effects.
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Solution
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========
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Being side effect free does not suffice for compile time evaluation. However,
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the evaluator can attempt to evaluate at compile time.
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