diff --git a/doc/manual/rl-next/pipe-operators.md b/doc/manual/rl-next/pipe-operators.md new file mode 100644 index 000000000..b4cbe30e3 --- /dev/null +++ b/doc/manual/rl-next/pipe-operators.md @@ -0,0 +1,28 @@ +--- +synopsis: "Add `pipe-operators` experimental feature" +prs: +- 11131 +--- + +This is a draft implementation of [RFC 0148](https://github.com/NixOS/rfcs/pull/148). + +The `pipe-operators` experimental feature adds [`<|` and `|>` operators][pipe operators] to the Nix language. +*a* `|>` *b* is equivalent to the function application *b* *a*, and +*a* `<|` *b* is equivalent to the function application *a* *b*. + +For example: + +``` +nix-repl> 1 |> builtins.add 2 |> builtins.mul 3 +9 + +nix-repl> builtins.add 1 <| builtins.mul 2 <| 3 +7 +``` + +`<|` and `|>` are right and left associative, respectively, and have lower precedence than any other operator. +These properties may change in future releases. + +See [the RFC](https://github.com/NixOS/rfcs/pull/148) for more examples and rationale. + +[pipe operators]: @docroot@/language/operators.md#pipe-operators diff --git a/doc/manual/src/language/operators.md b/doc/manual/src/language/operators.md index d2476c413..e96a28988 100644 --- a/doc/manual/src/language/operators.md +++ b/doc/manual/src/language/operators.md @@ -26,13 +26,17 @@ | Logical conjunction (`AND`) | *bool* `&&` *bool* | left | 12 | | Logical disjunction (`OR`) | *bool* \|\| *bool* | left | 13 | | [Logical implication] | *bool* `->` *bool* | right | 14 | +| [Pipe operator] (experimental) | *expr* `\|>` *func* | left | 15 | +| [Pipe operator] (experimental) | *func* `<\|` *expr* | right | 15 | [string]: ./types.md#type-string [path]: ./types.md#type-path -[number]: ./types.md#type-float +[number]: ./types.md#type-float [list]: ./types.md#list [attribute set]: ./types.md#attribute-set + + ## Attribute selection > **Syntax** @@ -176,3 +180,34 @@ Equivalent to `!`*b1* `||` *b2*. [Logical implication]: #logical-implication +## Pipe operators + +- *a* `|>` *b* is equivalent to *b* *a* +- *a* `<|` *b* is equivalent to *a* *b* + +> **Example** +> +> ``` +> nix-repl> 1 |> builtins.add 2 |> builtins.mul 3 +> 9 +> +> nix-repl> builtins.add 1 <| builtins.mul 2 <| 3 +> 7 +> ``` + +> **Warning** +> +> This syntax is part of an +> [experimental feature](@docroot@/contributing/experimental-features.md) +> and may change in future releases. +> +> To use this syntax, make sure the +> [`pipe-operators` experimental feature](@docroot@/contributing/experimental-features.md#xp-feature-pipe-operators) +> is enabled. +> For example, include the following in [`nix.conf`](@docroot@/command-ref/conf-file.md): +> +> ``` +> extra-experimental-features = pipe-operators +> ``` + +[Pipe operator]: #pipe-operators diff --git a/src/libexpr/lexer.l b/src/libexpr/lexer.l index 58401be8e..eb1825b7c 100644 --- a/src/libexpr/lexer.l +++ b/src/libexpr/lexer.l @@ -67,6 +67,14 @@ static StringToken unescapeStr(SymbolTable & symbols, char * s, size_t length) return {result, size_t(t - result)}; } +static void requireExperimentalFeature(const ExperimentalFeature & feature, const Pos & pos) +{ + if (!experimentalFeatureSettings.isEnabled(feature)) + throw ParseError(ErrorInfo{ + .msg = HintFmt("experimental Nix feature '%1%' is disabled; add '--extra-experimental-features %1%' to enable it", showExperimentalFeature(feature)), + .pos = pos, + }); +} } @@ -119,6 +127,12 @@ or { return OR_KW; } \-\> { return IMPL; } \/\/ { return UPDATE; } \+\+ { return CONCAT; } +\<\| { requireExperimentalFeature(Xp::PipeOperators, state->positions[CUR_POS]); + return PIPE_FROM; + } +\|\> { requireExperimentalFeature(Xp::PipeOperators, state->positions[CUR_POS]); + return PIPE_INTO; + } {ID} { yylval->id = {yytext, (size_t) yyleng}; return ID; } {INT} { errno = 0; diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y index 8ea176b24..9ad41c148 100644 --- a/src/libexpr/parser.y +++ b/src/libexpr/parser.y @@ -99,6 +99,14 @@ static void setDocPosition(const LexerState & lexerState, ExprLambda * lambda, P } } +static Expr * makeCall(PosIdx pos, Expr * fn, Expr * arg) { + if (auto e2 = dynamic_cast(fn)) { + e2->args.push_back(arg); + return fn; + } + return new ExprCall(pos, fn, {arg}); +} + %} @@ -123,6 +131,7 @@ static void setDocPosition(const LexerState & lexerState, ExprLambda * lambda, P %type start expr expr_function expr_if expr_op %type expr_select expr_simple expr_app +%type expr_pipe_from expr_pipe_into %type expr_list %type binds %type formals @@ -140,6 +149,7 @@ static void setDocPosition(const LexerState & lexerState, ExprLambda * lambda, P %token PATH HPATH SPATH PATH_END %token URI %token IF THEN ELSE ASSERT WITH LET IN_KW REC INHERIT EQ NEQ AND OR IMPL OR_KW +%token PIPE_FROM PIPE_INTO /* <| and |> */ %token DOLLAR_CURLY /* == ${ */ %token IND_STRING_OPEN IND_STRING_CLOSE %token ELLIPSIS @@ -206,9 +216,21 @@ expr_function expr_if : IF expr THEN expr ELSE expr { $$ = new ExprIf(CUR_POS, $2, $4, $6); } + | expr_pipe_from + | expr_pipe_into | expr_op ; +expr_pipe_from + : expr_op PIPE_FROM expr_pipe_from { $$ = makeCall(state->at(@2), $1, $3); } + | expr_op PIPE_FROM expr_op { $$ = makeCall(state->at(@2), $1, $3); } + ; + +expr_pipe_into + : expr_pipe_into PIPE_INTO expr_op { $$ = makeCall(state->at(@2), $3, $1); } + | expr_op PIPE_INTO expr_op { $$ = makeCall(state->at(@2), $3, $1); } + ; + expr_op : '!' expr_op %prec NOT { $$ = new ExprOpNot($2); } | '-' expr_op %prec NEGATE { $$ = new ExprCall(CUR_POS, new ExprVar(state->s.sub), {new ExprInt(0), $2}); } @@ -233,13 +255,7 @@ expr_op ; expr_app - : expr_app expr_select { - if (auto e2 = dynamic_cast($1)) { - e2->args.push_back($2); - $$ = $1; - } else - $$ = new ExprCall(CUR_POS, $1, {$2}); - } + : expr_app expr_select { $$ = makeCall(CUR_POS, $1, $2); } | expr_select ; diff --git a/src/libutil/experimental-features.cc b/src/libutil/experimental-features.cc index 1c080e372..a0c955816 100644 --- a/src/libutil/experimental-features.cc +++ b/src/libutil/experimental-features.cc @@ -24,7 +24,7 @@ struct ExperimentalFeatureDetails * feature, we either have no issue at all if few features are not added * at the end of the list, or a proper merge conflict if they are. */ -constexpr size_t numXpFeatures = 1 + static_cast(Xp::VerifiedFetches); +constexpr size_t numXpFeatures = 1 + static_cast(Xp::PipeOperators); constexpr std::array xpFeatureDetails = {{ { @@ -294,6 +294,14 @@ constexpr std::array xpFeatureDetails )", .trackingUrl = "https://github.com/NixOS/nix/milestone/48", }, + { + .tag = Xp::PipeOperators, + .name = "pipe-operators", + .description = R"( + Add `|>` and `<|` operators to the Nix language. + )", + .trackingUrl = "https://github.com/NixOS/nix/milestone/55", + }, }}; static_assert( diff --git a/src/libutil/experimental-features.hh b/src/libutil/experimental-features.hh index 6ffbc0c10..e65e51280 100644 --- a/src/libutil/experimental-features.hh +++ b/src/libutil/experimental-features.hh @@ -35,6 +35,7 @@ enum struct ExperimentalFeature ConfigurableImpureEnv, MountedSSHStore, VerifiedFetches, + PipeOperators, }; /** diff --git a/tests/functional/lang/eval-fail-pipe-operators.err.exp b/tests/functional/lang/eval-fail-pipe-operators.err.exp new file mode 100644 index 000000000..49f3fa8ad --- /dev/null +++ b/tests/functional/lang/eval-fail-pipe-operators.err.exp @@ -0,0 +1,5 @@ +error: experimental Nix feature 'pipe-operators' is disabled; add '--extra-experimental-features pipe-operators' to enable it + at /pwd/lang/eval-fail-pipe-operators.nix:1:3: + 1| 1 |> 2 + | ^ + 2| diff --git a/tests/functional/lang/eval-fail-pipe-operators.nix b/tests/functional/lang/eval-fail-pipe-operators.nix new file mode 100644 index 000000000..433e0fd7f --- /dev/null +++ b/tests/functional/lang/eval-fail-pipe-operators.nix @@ -0,0 +1 @@ +1 |> 2 diff --git a/tests/unit/libexpr/main.cc b/tests/unit/libexpr/main.cc index cf7fcf5a3..e3412d9ef 100644 --- a/tests/unit/libexpr/main.cc +++ b/tests/unit/libexpr/main.cc @@ -34,6 +34,9 @@ int main (int argc, char **argv) { setEnv("_NIX_TEST_NO_SANDBOX", "1"); #endif + // For pipe operator tests in trivial.cc + experimentalFeatureSettings.set("experimental-features", "pipe-operators"); + ::testing::InitGoogleTest(&argc, argv); return RUN_ALL_TESTS(); } diff --git a/tests/unit/libexpr/trivial.cc b/tests/unit/libexpr/trivial.cc index 61ea71a0f..e455a571b 100644 --- a/tests/unit/libexpr/trivial.cc +++ b/tests/unit/libexpr/trivial.cc @@ -182,6 +182,60 @@ namespace nix { ASSERT_THAT(v, IsIntEq(15)); } + TEST_F(TrivialExpressionTest, forwardPipe) { + auto v = eval("1 |> builtins.add 2 |> builtins.mul 3"); + ASSERT_THAT(v, IsIntEq(9)); + } + + TEST_F(TrivialExpressionTest, backwardPipe) { + auto v = eval("builtins.add 1 <| builtins.mul 2 <| 3"); + ASSERT_THAT(v, IsIntEq(7)); + } + + TEST_F(TrivialExpressionTest, forwardPipeEvaluationOrder) { + auto v = eval("1 |> null |> (x: 2)"); + ASSERT_THAT(v, IsIntEq(2)); + } + + TEST_F(TrivialExpressionTest, backwardPipeEvaluationOrder) { + auto v = eval("(x: 1) <| null <| 2"); + ASSERT_THAT(v, IsIntEq(1)); + } + + TEST_F(TrivialExpressionTest, differentPipeOperatorsDoNotAssociate) { + ASSERT_THROW(eval("(x: 1) <| 2 |> (x: 3)"), ParseError); + } + + TEST_F(TrivialExpressionTest, differentPipeOperatorsParensLeft) { + auto v = eval("((x: 1) <| 2) |> (x: 3)"); + ASSERT_THAT(v, IsIntEq(3)); + } + + TEST_F(TrivialExpressionTest, differentPipeOperatorsParensRight) { + auto v = eval("(x: 1) <| (2 |> (x: 3))"); + ASSERT_THAT(v, IsIntEq(1)); + } + + TEST_F(TrivialExpressionTest, forwardPipeLowestPrecedence) { + auto v = eval("false -> true |> (x: !x)"); + ASSERT_THAT(v, IsFalse()); + } + + TEST_F(TrivialExpressionTest, backwardPipeLowestPrecedence) { + auto v = eval("(x: !x) <| false -> true"); + ASSERT_THAT(v, IsFalse()); + } + + TEST_F(TrivialExpressionTest, forwardPipeStrongerThanElse) { + auto v = eval("if true then 1 else 2 |> 3"); + ASSERT_THAT(v, IsIntEq(1)); + } + + TEST_F(TrivialExpressionTest, backwardPipeStrongerThanElse) { + auto v = eval("if true then 1 else 2 <| 3"); + ASSERT_THAT(v, IsIntEq(1)); + } + TEST_F(TrivialExpressionTest, bindOr) { auto v = eval("{ or = 1; }"); ASSERT_THAT(v, IsAttrsOfSize(1));