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Make given clauses come last
We now forbid given clauses followed by normal parameter clauses. besides the syntactic awkwardness, there's also the problem of eta expansion. Example: ``` trait Universe { type T } def f given (u: Universe) (x: u.T) ``` How should we tea expand `f`? The usual algorithm would give: ``` (x: u.T) => (f given the[Universe])(x) ``` but that's ill typed, since `u` is not defined on the outside.
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‎compiler/src/dotty/tools/dotc/parsing/Parsers.scala‎

Lines changed: 18 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -2114,15 +2114,16 @@ object Parsers {
21142114
def typeParamClauseOpt(ownerKind: ParamOwner.Value): List[TypeDef] =
21152115
if (in.token == LBRACKET) typeParamClause(ownerKind) else Nil
21162116

2117-
/** ClsParamClause ::= [nl] [‘erased’] ‘(’ [ClsParams] ‘)’
2118-
* | ‘given’ [‘erased’] (‘(’ ClsParams ‘)’ | GivenTypes)
2119-
* ClsParams ::= ClsParam {`' ClsParam}
2120-
* ClsParam ::= {Annotation} [{ParamModifier} (`val' | `var') | `inline'] Param
2121-
* DefParamClause ::= [nl] [‘erased’] ‘(’ [DefParams] ‘)’ | GivenParamClause
2117+
/** ClsParamClause ::= [‘erased’] (‘(’ ClsParams ‘)’
2118+
* GivenClsParamClause::= ‘given’ [‘erased’] (‘(’ ClsParams ‘)’ | GivenTypes)
2119+
* ClsParams ::= ClsParam {‘,’ ClsParam}
2120+
* ClsParam ::= {Annotation}
2121+
*
2122+
* DefParamClause ::= [‘erased’] (‘(’ DefParams ‘)’
21222123
* GivenParamClause ::= ‘given’ [‘erased’] (‘(’ DefParams ‘)’ | GivenTypes)
2123-
* GivenTypes ::= RefinedType {`,' RefinedType}
2124-
* DefParams ::= DefParam {`,' DefParam}
2125-
* DefParam ::= {Annotation} [`inline'] Param
2124+
* DefParams ::= DefParam {‘,’ DefParam}
2125+
* DefParam ::= {Annotation} [‘inline’] Param
2126+
*
21262127
* Param ::= id `:' ParamType [`=' Expr]
21272128
*
21282129
* @return the list of parameter definitions
@@ -2204,14 +2205,16 @@ object Parsers {
22042205
}
22052206

22062207
/** ClsParamClauses ::= {ClsParamClause} [[nl] ‘(’ [‘implicit’] ClsParams ‘)’]
2208+
* | {ClsParamClause} {GivenClsParamClause}
22072209
* DefParamClauses ::= {DefParamClause} [[nl] ‘(’ [‘implicit’] DefParams ‘)’]
2210+
* | {DefParamClause} {GivenParamClause}
22082211
*
22092212
* @return The parameter definitions
22102213
*/
22112214
def paramClauses(ofClass: Boolean = false,
22122215
ofCaseClass: Boolean = false,
22132216
ofInstance: Boolean = false): List[List[ValDef]] = {
2214-
def recur(firstClause: Boolean, nparams: Int): List[List[ValDef]] = {
2217+
def recur(firstClause: Boolean, nparams: Int, contextualOnly: Boolean): List[List[ValDef]] = {
22152218
var initialMods = EmptyModifiers
22162219
if (in.token == GIVEN) {
22172220
in.nextToken()
@@ -2236,28 +2239,29 @@ object Parsers {
22362239
}
22372240
}
22382241
if (in.token == LPAREN && isParamClause) {
2239-
if (ofInstance && !isContextual)
2240-
syntaxError(em"parameters of instance definitions must come after `given'")
2242+
if (contextualOnly && !isContextual)
2243+
if (ofInstance) syntaxError(em"parameters of instance definitions must come after `given'")
2244+
else syntaxError(em"normal parameters cannot come after `given' clauses")
22412245
val params = paramClause(
22422246
ofClass = ofClass,
22432247
ofCaseClass = ofCaseClass,
22442248
firstClause = firstClause,
22452249
initialMods = initialMods)
22462250
val lastClause =
22472251
params.nonEmpty && params.head.mods.flags.is(Implicit, butNot = Given)
2248-
params :: (if (lastClause) Nil else recur(firstClause = false, nparams + params.length))
2252+
params :: (if (lastClause) Nil else recur(firstClause = false, nparams + params.length, isContextual))
22492253
}
22502254
else if (isContextual) {
22512255
val tps = commaSeparated(() => annotType())
22522256
var counter = nparams
22532257
def nextIdx = { counter += 1; counter }
22542258
val paramFlags = if (ofClass) Private | Local | ParamAccessor else Param
22552259
val params = tps.map(makeSyntheticParameter(nextIdx, _, paramFlags | Synthetic | Given | Implicit))
2256-
params :: recur(firstClause = false, nparams + params.length)
2260+
params :: recur(firstClause = false, nparams + params.length, isContextual)
22572261
}
22582262
else Nil
22592263
}
2260-
recur(firstClause = true, 0)
2264+
recur(firstClause = true, 0, ofInstance)
22612265
}
22622266

22632267
/* -------- DEFS ------------------------------------------- */

‎docs/docs/internals/syntax.md‎

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -292,16 +292,18 @@ HkTypeParam ::= {Annotation} [‘+’ | ‘-’] (Id[HkTypeParamClause] |
292292
SubtypeBounds
293293
294294
ClsParamClauses ::= {ClsParamClause} [[nl] ‘(’ [‘implicit’] ClsParams ‘)’]
295-
ClsParamClause ::= [nl] [‘erased’] ‘(’ [ClsParams] ‘)’
296-
| ‘given’ [‘erased’] (‘(’ ClsParams ‘)’ | GivenTypes)
295+
| {ClsParamClause} {GivenClsParamClause}
296+
ClsParamClause ::= [‘erased’] (‘(’ ClsParams ‘)’
297+
GivenClsParamClause::= ‘given’ [‘erased’] (‘(’ ClsParams ‘)’ | GivenTypes)
297298
ClsParams ::= ClsParam {‘,’ ClsParam}
298299
ClsParam ::= {Annotation} ValDef(mods, id, tpe, expr) -- point of mods on val/var
299300
[{Modifier} (‘val’ | ‘var’) | ‘inline’] Param
300301
Param ::= id ‘:’ ParamType [‘=’ Expr]
301302
| INT
302303
303304
DefParamClauses ::= {DefParamClause} [[nl] ‘(’ [‘implicit’] DefParams ‘)’]
304-
DefParamClause ::= [nl] [‘erased’] ‘(’ [DefParams] ‘)’ | GivenParamClause
305+
| {DefParamClause} {GivenParamClause}
306+
DefParamClause ::= [‘erased’] (‘(’ DefParams ‘)’
305307
GivenParamClause ::= ‘given’ [‘erased’] (‘(’ DefParams ‘)’ | GivenTypes)
306308
DefParams ::= DefParam {‘,’ DefParam}
307309
DefParam ::= {Annotation} [‘inline’] Param ValDef(mods, id, tpe, expr) -- point of mods at id.

‎docs/docs/reference/contextual/inferable-params.md‎

Lines changed: 22 additions & 20 deletions
Original file line numberDiff line numberDiff line change
@@ -64,24 +64,25 @@ maximum(xs) given (descending given ListOrd)
6464
maximum(xs) given (descending given (ListOrd given IntOrd))
6565
```
6666

67-
## Mixing Given Clauses And Normal Parameters
67+
## Multiple Given Clauses
6868

69-
Given clauses can be freely mixed with normal parameters.
70-
A given clause may be followed by a normal parameter and _vice versa_.
7169
There can be several given clauses in a definition. Example:
7270
```scala
73-
def f given (u: Universe) (x: u.T) given Context = ...
74-
75-
implied global for Universe { type T = String ... }
76-
implied ctx for Context { ... }
71+
def f given (u: Universe) given (x: u.Context) = ...
72+
```
73+
However, all `given` clauses in a definition must come after any normal parameter clauses.
74+
Multiple given clauses are matched left-to-right in applications. Example:
75+
```scala
76+
implied global for Universe { type Context = ... }
77+
implied ctx for global.Context { ... }
7778
```
7879
Then the following calls are all valid (and normalize to the last one)
7980
```scala
80-
f("abc")
81-
(f given global)("abc")
82-
f("abc") given ctx
83-
(f given global)("abc") given ctx
81+
f
82+
(f given global)
83+
(f given global) given ctx
8484
```
85+
But `f given ctx` would give a type error.
8586

8687
## Summoning Implied Instances
8788

@@ -100,13 +101,14 @@ Functions like `the` that have only context parameters are also called _context
100101

101102
Here is the new syntax of parameters and arguments seen as a delta from the [standard context free syntax of Scala 3](http://dotty.epfl.ch/docs/internals/syntax.html).
102103
```
103-
ClsParamClause ::= ...
104-
| ‘given’ (‘(’ [ClsParams] ‘)’ | GivenTypes)
105-
DefParamClause ::= ...
106-
| GivenParamClause
107-
GivenParamClause ::= ‘given’ (‘(’ DefParams ‘)’ | GivenTypes)
108-
GivenTypes ::= AnnotType {‘,’ AnnotType}
109-
110-
InfixExpr ::= ...
111-
| InfixExpr ‘given’ (InfixExpr | ParArgumentExprs)
104+
ClsParamClauses ::= ...
105+
| {ClsParamClause} {GivenClsParamClause}
106+
GivenClsParamClause ::= ‘given’ [‘erased’] (‘(’ ClsParams ‘)’ | GivenTypes)
107+
DefParamClauses ::= ...
108+
| {DefParamClause} {GivenParamClause}
109+
GivenParamClause ::= ‘given’ [‘erased’] (‘(’ DefParams ‘)’ | GivenTypes)
110+
GivenTypes ::= AnnotType {‘,’ AnnotType}
111+
112+
InfixExpr ::= ...
113+
| InfixExpr ‘given’ (InfixExpr | ParArgumentExprs)
112114
```

‎tests/neg/implicit-params.scala‎

Lines changed: 12 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1,24 +1,28 @@
11
object Test {
22

33
case class C(x: Int)
4+
case class D(x: Int)
45

56
def f(x: Int) given (c: C) = x + c.x
67

7-
def g(x: Int) given (c: C) (y: Int) = x + c.x + y
8+
def g0(x: Int) given (c: C) (y: Int) = x + c.x + y // error
9+
10+
def g(x: Int) given (c: C) given D = x + c.x + the[D].x // OK
811

912
def h(x: Int) given () = x // error
1013

11-
implicit object C extends C(11)
14+
implied C for C(11)
15+
implied D for D(11)
1216

1317
f(1)
1418
f(1) given C
1519
f given 2 // error
1620
f(1)(C) // error
1721

18-
g(1)(2) // OK
19-
(g(1) given C)(2) // OK
20-
g(1) given 2 // error
21-
g(1) given C given 2 // error
22-
g(1)(C)(2) // error
23-
g(1)(C) given 2 // error
22+
g(1) // OK
23+
g(1) given C // OK
24+
g(1) given C given D(0) // OK
25+
g(1) given D // error
26+
g(1)(D) // error
27+
g(1)(C)(D) // error
2428
}

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