ForExpr
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{{XXX|Define the expansion of ForExpr}} | {{XXX|Define the expansion of ForExpr}} | ||
| - | + | == Static constraints == | |
| + | |||
| + | * <var>collection</var> may not use nouns bound by <var>optKeyPattern</var> or <var>valuePattern</var>, or vice versa. | ||
| + | |||
| + | == Tests == | ||
| + | |||
| + | The function provided to (the value of <var>collection</var>)'s [[:Category:Message iterate/1|iterate/1]] method throws if called after iterate/1 has returned. | ||
| + | |||
| + | ? var captured := null | ||
| + | ? def capturer { | ||
| + | > to iterate(f) :void { | ||
| + | > captured := f | ||
| + | > f("a", "b") | ||
| + | > } | ||
| + | > } | ||
| + | # value: <capturer> | ||
| + | |||
| + | ? for x => y in capturer { println(x, " -> ", y) } | ||
| + | # stdout: a -> b | ||
| + | # | ||
| + | |||
| + | ? captured("c", "d") | ||
| + | # problem: For-loop body isn't valid after for-loop exits. | ||
| + | |||
| + | The return value of iterate/1 is not the return value of the for loop; the loop returns [[null]] unless a return value is given by [[__break]]. | ||
| + | |||
| + | ? def confuser extends [1,2,3] { | ||
| + | > to iterate(f) { | ||
| + | > super.iterate(f) | ||
| + | > return __Portrayal | ||
| + | > } | ||
| + | > } | ||
| + | # value: <confuser> | ||
| + | |||
| + | ? def optKeyOf(collection, toFind) { | ||
| + | > return for key => val in collection { | ||
| + | > if (val == toFind) { | ||
| + | > break key | ||
| + | > } | ||
| + | > } | ||
| + | > } | ||
| + | |||
| + | ? optKeyOf(confuser, 1) | ||
| + | # value: 0 | ||
| + | |||
| + | ? [optKeyOf(confuser, 43)] | ||
| + | # value: [null] | ||
| + | |||
| + | |||
| + | [[Category:E language specification]] | ||
| + | [[Category:Nonkernel-E nodes]] | ||
Latest revision as of 18:44, 20 April 2011
ForExpr is a nonkernel node which executes code for each element in a collection or other object implementing iterate/1.
"for" (optKeyPattern "=>")? valuePattern "in" collection "{" body "}" ({optBreakCatch an EMatcher}: "catch" pattern "{" expr "}")?
XXX We need to formalize the grammar definitions used in our spec
Contents |
Fields
- optKeyPattern :nullOk[Pattern]
- valuePattern :Pattern
- collection :nullOk[EExpr]
- body :EExpr
- optBreakCatch :nullOk[EMatcher]
Expansion
XXX Define the expansion of ForExpr
Static constraints
- collection may not use nouns bound by optKeyPattern or valuePattern, or vice versa.
Tests
The function provided to (the value of collection)'s iterate/1 method throws if called after iterate/1 has returned.
? var captured := null
? def capturer {
> to iterate(f) :void {
> captured := f
> f("a", "b")
> }
> }
# value: <capturer>
? for x => y in capturer { println(x, " -> ", y) }
# stdout: a -> b
#
? captured("c", "d")
# problem: For-loop body isn't valid after for-loop exits.
The return value of iterate/1 is not the return value of the for loop; the loop returns null unless a return value is given by __break.
? def confuser extends [1,2,3] {
> to iterate(f) {
> super.iterate(f)
> return __Portrayal
> }
> }
# value: <confuser>
? def optKeyOf(collection, toFind) {
> return for key => val in collection {
> if (val == toFind) {
> break key
> }
> }
> }
? optKeyOf(confuser, 1)
# value: 0
? [optKeyOf(confuser, 43)]
# value: [null]
