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Clean up when/is evaluation

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David Schmenk 2018-09-26 15:51:35 -07:00 committed by GitHub
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@ -518,7 +518,7 @@ else
fin fin
``` ```
The `when`/`is`/`otherwise`/`wend` statement is similar to the `if`/`elsif`/`else`/`fin` construct except that it is more efficient. It selects one path based on the evaluated expressions, then merges the code path back together at the end. Only the `when` value is compared against a list of expressions. The expressions do not need to be constants, they can be any valid expression. The list of expressions is evaluated in order, so for efficiency sake, place the most common cases earlier in the list. Just as in C programs, a `break` statement is required to keep one clause from falling through to the next. Falling through from one clause to the next can have its uses, so this behavior has been added to PLASMA. The `when`/`is`/`otherwise`/`wend` statement is similar to the `if`/`elsif`/`else`/`fin` construct except that it is more efficient. It selects one path based on the evaluated expressions, then merges the code path back together at the end. Only the `when` value is compared against a list of constant. Just as in C programs, a `break` statement is required to keep one clause from falling through to the next. Falling through from one clause to the next can have its uses, so this behavior has been added to PLASMA.
``` ```
when keypressed when keypressed
@ -1139,7 +1139,7 @@ The common `if` test can have optional `elsif` and/or `else` clauses. Any expres
#### WHEN/IS/[OTHERWISE]/WEND #### WHEN/IS/[OTHERWISE]/WEND
The complex test case is handled with `when`. Basically an `if`, `elsif`, `else` list of comparisons, it is generally more efficient. The `is` value can be any expression. It is evaluated and tested for equality to the `when` value. The complex test case is handled with `when`. Basically an `if`, `elsif`, `else` list of comparisons, it is generally more efficient. The `is` value must be a constant.
``` ```
when key when key
@ -1162,26 +1162,6 @@ when key
wend wend
``` ```
With a little "Yoda-Speak", some fairly complex test can be made:
```
const FALSE = 0
const TRUE = NOT FALSE
byte a
when TRUE
is (a <= 10)
// 10 or less
break
is (a > 10) AND (a < 20)
// between 10 and 20
break
is (a >= 20)
// 20 or greater
wend
```
A `when` clause can fall-through to the following clause, just like C `switch` statements by leaving out the `break`. A `when` clause can fall-through to the following clause, just like C `switch` statements by leaving out the `break`.
#### FOR \<TO,DOWNTO\> [STEP]/NEXT #### FOR \<TO,DOWNTO\> [STEP]/NEXT