64 lines
1.6 KiB
Markdown
64 lines
1.6 KiB
Markdown
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# Type checking
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Granite contains two types: integers and strings, and due to how some operations work it may be worth type checking these explicitly within the code.
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## New operations
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* `:&(variable),(output)`, type check, if `(variable)` is an integer then set `(output)` to 1 otherwise set `(output)` to 0
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## Tutorial
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Look at this simple program:
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```
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:?x
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:^x
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:!x
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```
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This program simply asks the user for a number and adds 1 to it.
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This program works fine _provided the user inputs a number_.
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```
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? 50
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51
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```
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But things begin to fall apart if the user does not input an integer.
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```
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? I'm an evil string! >:)
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Non-number variable x on increment.
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```
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Type checking can solve this problem by allowing the programmer to safely recover when an invalid type is detected.
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Firstly, we want to make the question a label so make a label called `question` above `:?x`.
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Also add a [variable drop](dropping-variables.md) after the `question` label but _before_ asking the user for `x`.
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Now directly after `:?x` but _before_ `:^x` we want to add the type check operation so add `:&x,type` after `:?x`.
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Now we will have an integer corresponding to whether `x` is an integer or not. So _now_ after `:&x,type` you can add a conditional jump that jumps to the `question` label if `type` is equal to `0` which means that the user inputted a string.
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Now our program is immune to strings messing things up:
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```
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? I'm an evil string! >:)
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? No strings? :(
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? 10
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11
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```
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## Extension
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Can you prompt the user to input an integer after incorrectly putting in a string?
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## After example
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```
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:@question
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:$x
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:?x
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:&x,type
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:=question,type,0
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:^x
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:!x
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```
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