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| author | Som Snytt <som.snytt@gmail.com> | 2014-03-28 17:22:44 -0700 |
|---|---|---|
| committer | Adriaan Moors <adriaan.moors@typesafe.com> | 2014-03-28 17:40:58 -0700 |
| commit | 91fb5c07bdda40feb5ac933bc07357a17eb015b4 (patch) | |
| tree | 816f8cf33f34b8ac8344ecb2e13f2ded65a6a2e8 /spec | |
| parent | b3adae60f1834dca50ba002e89ac85efb7466896 (diff) | |
| download | scala-91fb5c07bdda40feb5ac933bc07357a17eb015b4.tar.gz scala-91fb5c07bdda40feb5ac933bc07357a17eb015b4.tar.bz2 scala-91fb5c07bdda40feb5ac933bc07357a17eb015b4.zip | |
SI-6054 Modern eta-expansion examples that almost run
This wasn't so easy after all. The clever one is to show
that `Option.fold(=>Z)` preserves the by-nameness of the zero value,
which may or may not be in the spec yet.
The addition to 6.26.5 was (I think) rejected as implementation-specific;
it should use the wording from 6.6 about "preserving by-nameness" or "by-namity"
(the latter has the advantage of sounding both more technical and somewhat inane).
Diffstat (limited to 'spec')
| -rw-r--r-- | spec/06-expressions.md | 17 |
1 files changed, 8 insertions, 9 deletions
diff --git a/spec/06-expressions.md b/spec/06-expressions.md index 89154d4441..b2144aac6d 100644 --- a/spec/06-expressions.md +++ b/spec/06-expressions.md @@ -266,7 +266,7 @@ The function $f$ must be _applicable_ to its arguments $e_1 If $f$ has a method type $(p_1:T_1 , \ldots , p_n:T_n)U$ we say that an argument expression $e_i$ is a _named_ argument if it has the form $x_i=e'_i$ and $x_i$ is one of the parameter names -$p_1 , \ldots , p_n$. The function $f$ is applicable if all of the follwing conditions +$p_1 , \ldots , p_n$. The function $f$ is applicable if all of the following conditions hold: - For every named argument $x_i=e'_i$ the type $S_i$ @@ -438,14 +438,13 @@ parameterlist `()`. ###### Example The method values in the left column are each equivalent to the [eta-expanded expressions](#eta-expansion) on the right. -| placeholder syntax | eta-expansion | -|------------------------------ | --------------------------------------------| -|`Math.sin _` | `x => Math.sin(x)` | -|`Array.range _` | `(x1, x2) => Array.range(x1, x2)` | -|`map2 _` | `(x1, x2) => (x3) => map2(x1, x2)(x3)` | -|`map2(xs, ys)_` | `{ val eta1 = xs; val eta2 = ys; x => map2(eta1, eta2)(x) }` | - -This assumes a method `def map2[A, B, C](xs: List[A], ys: List[B])(f: (A, B) => C): List[C]`. +| placeholder syntax | eta-expansion | +|------------------------------ | ----------------------------------------------------------------------------| +|`math.sin _` | `x => math.sin(x)` | +|`math.pow _` | `(x1, x2) => math.pow(x1, x2)` | +|`val vs = 1 to 9; vs.fold _` | `(z) => (op) => vs.fold(z)(op)` | +|`(1 to 9).fold(z)_` | `{ val eta1 = z; val eta2 = 1 to 9; op => eta2.fold(eta1)(op) }` | +|`Some(1).fold(??? : Int)_` | `{ val eta1 = () => ???; val eta2 = Some(1); op => eta2.fold(eta1())(op) }` | Note that a space is necessary between a method name and the trailing underscore |