diff --git a/src/doc/reference.md b/src/doc/reference.md index 12e756fc26b..131637948c8 100644 --- a/src/doc/reference.md +++ b/src/doc/reference.md @@ -2488,6 +2488,8 @@ The currently implemented features of the reference compiler are: * `if_let` - Allows use of the `if let` syntax. +* `while_let` - Allows use of the `while let` syntax. + * `intrinsics` - Allows use of the "rust-intrinsics" ABI. Compiler intrinsics are inherently unstable and no promise about them is made. @@ -3494,6 +3496,18 @@ of a condition expression it expects a refutable let statement. If the value of expression on the right hand side of the let statement matches the pattern, the corresponding block will execute, otherwise flow proceeds to the first `else` block that follows. +### While let loops + +```{.ebnf .gram} +while_let_expr : "while" "let" pat '=' expr '{' block '}' ; +``` + +A `while let` loop is semantically identical to a `while` loop but in place of a +condition expression it expects a refutable let statement. If the value of the +expression on the right hand side of the let statement matches the pattern, the +loop body block executes and control returns to the pattern matching statement. +Otherwise, the while expression completes. + ### Return expressions ```{.ebnf .gram} diff --git a/src/librustc/diagnostics.rs b/src/librustc/diagnostics.rs index 31dff0b1471..c392d92a83f 100644 --- a/src/librustc/diagnostics.rs +++ b/src/librustc/diagnostics.rs @@ -145,5 +145,6 @@ register_diagnostics!( E0161, E0162, E0163, - E0164 + E0164, + E0165 ) diff --git a/src/librustc/lint/builtin.rs b/src/librustc/lint/builtin.rs index e0e16390e35..988b128e31d 100644 --- a/src/librustc/lint/builtin.rs +++ b/src/librustc/lint/builtin.rs @@ -1082,7 +1082,8 @@ impl LintPass for UnnecessaryParens { ast::ExprWhile(ref cond, _, _) => (cond, "`while` condition", true), ast::ExprMatch(ref head, _, source) => match source { ast::MatchNormal => (head, "`match` head expression", true), - ast::MatchIfLetDesugar => (head, "`if let` head expression", true) + ast::MatchIfLetDesugar => (head, "`if let` head expression", true), + ast::MatchWhileLetDesugar => (head, "`while let` head expression", true), }, ast::ExprRet(Some(ref value)) => (value, "`return` value", false), ast::ExprAssign(_, ref value) => (value, "assigned value", false), diff --git a/src/librustc/middle/cfg/construct.rs b/src/librustc/middle/cfg/construct.rs index a9a3981ab5f..b573c4e5948 100644 --- a/src/librustc/middle/cfg/construct.rs +++ b/src/librustc/middle/cfg/construct.rs @@ -259,6 +259,10 @@ impl<'a, 'tcx> CFGBuilder<'a, 'tcx> { expr_exit } + ast::ExprWhileLet(..) => { + self.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } + ast::ExprForLoop(ref pat, ref head, ref body, _) => { // // [pred] diff --git a/src/librustc/middle/check_match.rs b/src/librustc/middle/check_match.rs index 16329fe9c65..84367090b26 100644 --- a/src/librustc/middle/check_match.rs +++ b/src/librustc/middle/check_match.rs @@ -261,20 +261,32 @@ fn check_arms(cx: &MatchCheckCtxt, arms: &[(Vec>, Option<&Expr>)], source match is_useful(cx, &seen, v.as_slice(), LeaveOutWitness) { NotUseful => { - if source == MatchIfLetDesugar { - if printed_if_let_err { - // we already printed an irrefutable if-let pattern error. - // We don't want two, that's just confusing. - } else { + match source { + MatchIfLetDesugar => { + if printed_if_let_err { + // we already printed an irrefutable if-let pattern error. + // We don't want two, that's just confusing. + } else { + // find the first arm pattern so we can use its span + let &(ref first_arm_pats, _) = &arms[0]; + let first_pat = first_arm_pats.get(0); + let span = first_pat.span; + span_err!(cx.tcx.sess, span, E0162, "irrefutable if-let pattern"); + printed_if_let_err = true; + } + }, + + MatchWhileLetDesugar => { // find the first arm pattern so we can use its span let &(ref first_arm_pats, _) = &arms[0]; let first_pat = first_arm_pats.get(0); let span = first_pat.span; - span_err!(cx.tcx.sess, span, E0162, "irrefutable if-let pattern"); - printed_if_let_err = true; - } - } else { - span_err!(cx.tcx.sess, pat.span, E0001, "unreachable pattern"); + span_err!(cx.tcx.sess, span, E0165, "irrefutable while-let pattern"); + }, + + MatchNormal => { + span_err!(cx.tcx.sess, pat.span, E0001, "unreachable pattern") + }, } } Useful => (), diff --git a/src/librustc/middle/expr_use_visitor.rs b/src/librustc/middle/expr_use_visitor.rs index 6cfdac93efc..6f179e0624f 100644 --- a/src/librustc/middle/expr_use_visitor.rs +++ b/src/librustc/middle/expr_use_visitor.rs @@ -429,6 +429,10 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,TYPER> { self.walk_block(&**blk); } + ast::ExprWhileLet(..) => { + self.tcx().sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } + ast::ExprForLoop(ref pat, ref head, ref blk, _) => { // The pattern lives as long as the block. debug!("walk_expr for loop case: blk id={}", blk.id); diff --git a/src/librustc/middle/liveness.rs b/src/librustc/middle/liveness.rs index 2176cd56589..90973dfaa00 100644 --- a/src/librustc/middle/liveness.rs +++ b/src/librustc/middle/liveness.rs @@ -484,6 +484,9 @@ fn visit_expr(ir: &mut IrMaps, expr: &Expr) { ExprIfLet(..) => { ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet"); } + ExprWhileLet(..) => { + ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } ExprForLoop(ref pat, _, _, _) => { pat_util::pat_bindings(&ir.tcx.def_map, &**pat, |bm, p_id, sp, path1| { debug!("adding local variable {} from for loop with bm {:?}", @@ -1022,6 +1025,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> { self.propagate_through_loop(expr, WhileLoop(&**cond), &**blk, succ) } + ExprWhileLet(..) => { + self.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } + ExprForLoop(ref pat, ref head, ref blk, _) => { let ln = self.propagate_through_loop(expr, ForLoop(&**pat), &**blk, succ); self.propagate_through_expr(&**head, ln) @@ -1480,6 +1487,9 @@ fn check_expr(this: &mut Liveness, expr: &Expr) { ExprIfLet(..) => { this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet"); } + ExprWhileLet(..) => { + this.ir.tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } } } diff --git a/src/librustc/middle/mem_categorization.rs b/src/librustc/middle/mem_categorization.rs index fa494b357c1..4a1c4aaa895 100644 --- a/src/librustc/middle/mem_categorization.rs +++ b/src/librustc/middle/mem_categorization.rs @@ -530,6 +530,9 @@ impl<'t,'tcx,TYPER:Typer<'tcx>> MemCategorizationContext<'t,TYPER> { ast::ExprIfLet(..) => { self.tcx().sess.span_bug(expr.span, "non-desugared ExprIfLet"); } + ast::ExprWhileLet(..) => { + self.tcx().sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } } } diff --git a/src/librustc/middle/trans/debuginfo.rs b/src/librustc/middle/trans/debuginfo.rs index 43c98998299..d81f78f23ff 100644 --- a/src/librustc/middle/trans/debuginfo.rs +++ b/src/librustc/middle/trans/debuginfo.rs @@ -3496,6 +3496,11 @@ fn populate_scope_map(cx: &CrateContext, }) } + ast::ExprWhileLet(..) => { + cx.sess().span_bug(exp.span, "debuginfo::populate_scope_map() - \ + Found unexpanded while-let."); + } + ast::ExprForLoop(ref pattern, ref head, ref body, _) => { walk_expr(cx, &**head, scope_stack, scope_map); diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs index 071f6b12684..1185c644978 100644 --- a/src/librustc/middle/ty.rs +++ b/src/librustc/middle/ty.rs @@ -3605,6 +3605,9 @@ pub fn expr_kind(tcx: &ctxt, expr: &ast::Expr) -> ExprKind { ast::ExprIfLet(..) => { tcx.sess.span_bug(expr.span, "non-desugared ExprIfLet"); } + ast::ExprWhileLet(..) => { + tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } ast::ExprLit(ref lit) if lit_is_str(&**lit) => { RvalueDpsExpr diff --git a/src/librustc/middle/typeck/check/mod.rs b/src/librustc/middle/typeck/check/mod.rs index ed663cb85a2..b78398fdb6d 100644 --- a/src/librustc/middle/typeck/check/mod.rs +++ b/src/librustc/middle/typeck/check/mod.rs @@ -4058,6 +4058,9 @@ fn check_expr_with_unifier(fcx: &FnCtxt, fcx.write_nil(id); } } + ast::ExprWhileLet(..) => { + tcx.sess.span_bug(expr.span, "non-desugared ExprWhileLet"); + } ast::ExprForLoop(ref pat, ref head, ref block, _) => { check_expr(fcx, &**head); let typ = lookup_method_for_for_loop(fcx, &**head, expr.id); diff --git a/src/librustc/util/ppaux.rs b/src/librustc/util/ppaux.rs index 6898eb17e91..459e7eb093e 100644 --- a/src/librustc/util/ppaux.rs +++ b/src/librustc/util/ppaux.rs @@ -93,6 +93,9 @@ pub fn explain_region_and_span(cx: &ctxt, region: ty::Region) explain_span(cx, "method call", expr.span) }, ast::ExprMatch(_, _, ast::MatchIfLetDesugar) => explain_span(cx, "if let", expr.span), + ast::ExprMatch(_, _, ast::MatchWhileLetDesugar) => { + explain_span(cx, "while let", expr.span) + }, ast::ExprMatch(..) => explain_span(cx, "match", expr.span), _ => explain_span(cx, "expression", expr.span) } diff --git a/src/librustc_back/svh.rs b/src/librustc_back/svh.rs index 35e42e3c54b..3c28cac6c6f 100644 --- a/src/librustc_back/svh.rs +++ b/src/librustc_back/svh.rs @@ -294,6 +294,7 @@ mod svh_visitor { // just syntactic artifacts, expanded away by time of SVH. ExprIfLet(..) => unreachable!(), + ExprWhileLet(..) => unreachable!(), ExprMac(..) => unreachable!(), } } diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs index 44b327745ed..bf4734529a2 100644 --- a/src/libsyntax/ast.rs +++ b/src/libsyntax/ast.rs @@ -524,6 +524,8 @@ pub enum Expr_ { // FIXME #6993: change to Option ... or not, if these are hygienic. ExprWhile(P, P, Option), // FIXME #6993: change to Option ... or not, if these are hygienic. + ExprWhileLet(P, P, P, Option), + // FIXME #6993: change to Option ... or not, if these are hygienic. ExprForLoop(P, P, P, Option), // Conditionless loop (can be exited with break, cont, or ret) // FIXME #6993: change to Option ... or not, if these are hygienic. @@ -579,7 +581,8 @@ pub struct QPath { #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)] pub enum MatchSource { MatchNormal, - MatchIfLetDesugar + MatchIfLetDesugar, + MatchWhileLetDesugar, } #[deriving(Clone, PartialEq, Eq, Encodable, Decodable, Hash, Show)] diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs index 87983e1aea3..98ac6fe6a6c 100644 --- a/src/libsyntax/ext/build.rs +++ b/src/libsyntax/ext/build.rs @@ -147,6 +147,8 @@ pub trait AstBuilder { fn expr_some(&self, sp: Span, expr: P) -> P; fn expr_none(&self, sp: Span) -> P; + fn expr_break(&self, sp: Span) -> P; + fn expr_tuple(&self, sp: Span, exprs: Vec>) -> P; fn expr_fail(&self, span: Span, msg: InternedString) -> P; @@ -688,6 +690,12 @@ impl<'a> AstBuilder for ExtCtxt<'a> { self.expr_path(none) } + + fn expr_break(&self, sp: Span) -> P { + self.expr(sp, ast::ExprBreak(None)) + } + + fn expr_tuple(&self, sp: Span, exprs: Vec>) -> P { self.expr(sp, ast::ExprTup(exprs)) } diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs index efe4b76354f..575dcf32dd6 100644 --- a/src/libsyntax/ext/expand.rs +++ b/src/libsyntax/ext/expand.rs @@ -67,6 +67,42 @@ pub fn expand_expr(e: P, fld: &mut MacroExpander) -> P { fld.cx.expr(span, ast::ExprWhile(cond, body, opt_ident)) } + // Desugar ExprWhileLet + // From: `[opt_ident]: while let = ` + ast::ExprWhileLet(pat, expr, body, opt_ident) => { + // to: + // + // [opt_ident]: loop { + // match { + // => , + // _ => break + // } + // } + + // ` => ` + let pat_arm = { + let body_expr = fld.cx.expr_block(body); + fld.cx.arm(pat.span, vec![pat], body_expr) + }; + + // `_ => break` + let break_arm = { + let pat_under = fld.cx.pat_wild(span); + let break_expr = fld.cx.expr_break(span); + fld.cx.arm(span, vec![pat_under], break_expr) + }; + + // `match { ... }` + let arms = vec![pat_arm, break_arm]; + let match_expr = fld.cx.expr(span, + ast::ExprMatch(expr, arms, ast::MatchWhileLetDesugar)); + + // `[opt_ident]: loop { ... }` + let loop_block = fld.cx.block_expr(match_expr); + let (loop_block, opt_ident) = expand_loop_block(loop_block, opt_ident, fld); + fld.cx.expr(span, ast::ExprLoop(loop_block, opt_ident)) + } + // Desugar ExprIfLet // From: `if let = []` ast::ExprIfLet(pat, expr, body, mut elseopt) => { diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs index 590157d677d..c1877c827a4 100644 --- a/src/libsyntax/feature_gate.rs +++ b/src/libsyntax/feature_gate.rs @@ -73,6 +73,7 @@ static KNOWN_FEATURES: &'static [(&'static str, Status)] = &[ ("slicing_syntax", Active), ("if_let", Active), + ("while_let", Active), // if you change this list without updating src/doc/reference.md, cmr will be sad @@ -345,6 +346,10 @@ impl<'a, 'v> Visitor<'v> for Context<'a> { e.span, "slicing syntax is experimental"); } + ast::ExprWhileLet(..) => { + self.gate_feature("while_let", e.span, + "`while let` syntax is experimental"); + } _ => {} } visit::walk_expr(self, e); diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs index 3e16bca72ef..8faecd407a8 100644 --- a/src/libsyntax/fold.rs +++ b/src/libsyntax/fold.rs @@ -1216,6 +1216,12 @@ pub fn noop_fold_expr(Expr {id, node, span}: Expr, folder: &mut T) -> folder.fold_block(body), opt_ident.map(|i| folder.fold_ident(i))) } + ExprWhileLet(pat, expr, body, opt_ident) => { + ExprWhileLet(folder.fold_pat(pat), + folder.fold_expr(expr), + folder.fold_block(body), + opt_ident.map(|i| folder.fold_ident(i))) + } ExprForLoop(pat, iter, body, opt_ident) => { ExprForLoop(folder.fold_pat(pat), folder.fold_expr(iter), diff --git a/src/libsyntax/parse/classify.rs b/src/libsyntax/parse/classify.rs index cb57318445e..d46d078c776 100644 --- a/src/libsyntax/parse/classify.rs +++ b/src/libsyntax/parse/classify.rs @@ -28,6 +28,7 @@ pub fn expr_requires_semi_to_be_stmt(e: &ast::Expr) -> bool { | ast::ExprMatch(..) | ast::ExprBlock(_) | ast::ExprWhile(..) + | ast::ExprWhileLet(..) | ast::ExprLoop(..) | ast::ExprForLoop(..) => false, _ => true diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs index 460e96a6ad8..d5253cff6cb 100644 --- a/src/libsyntax/parse/parser.rs +++ b/src/libsyntax/parse/parser.rs @@ -26,7 +26,7 @@ use ast::{ExprField, ExprTupField, ExprFnBlock, ExprIf, ExprIfLet, ExprIndex, Ex use ast::{ExprLit, ExprLoop, ExprMac}; use ast::{ExprMethodCall, ExprParen, ExprPath, ExprProc}; use ast::{ExprRepeat, ExprRet, ExprStruct, ExprTup, ExprUnary, ExprUnboxedFn}; -use ast::{ExprVec, ExprWhile, ExprForLoop, Field, FnDecl}; +use ast::{ExprVec, ExprWhile, ExprWhileLet, ExprForLoop, Field, FnDecl}; use ast::{Once, Many}; use ast::{FnUnboxedClosureKind, FnMutUnboxedClosureKind}; use ast::{FnOnceUnboxedClosureKind}; @@ -2935,7 +2935,11 @@ impl<'a> Parser<'a> { self.mk_expr(lo, hi, ExprForLoop(pat, expr, loop_block, opt_ident)) } + /// Parse a 'while' or 'while let' expression ('while' token already eaten) pub fn parse_while_expr(&mut self, opt_ident: Option) -> P { + if self.is_keyword(keywords::Let) { + return self.parse_while_let_expr(opt_ident); + } let lo = self.last_span.lo; let cond = self.parse_expr_res(RESTRICTION_NO_STRUCT_LITERAL); let body = self.parse_block(); @@ -2943,6 +2947,18 @@ impl<'a> Parser<'a> { return self.mk_expr(lo, hi, ExprWhile(cond, body, opt_ident)); } + /// Parse a 'while let' expression ('while' token already eaten) + pub fn parse_while_let_expr(&mut self, opt_ident: Option) -> P { + let lo = self.last_span.lo; + self.expect_keyword(keywords::Let); + let pat = self.parse_pat(); + self.expect(&token::EQ); + let expr = self.parse_expr_res(RESTRICTION_NO_STRUCT_LITERAL); + let body = self.parse_block(); + let hi = body.span.hi; + return self.mk_expr(lo, hi, ExprWhileLet(pat, expr, body, opt_ident)); + } + pub fn parse_loop_expr(&mut self, opt_ident: Option) -> P { let lo = self.last_span.lo; let body = self.parse_block(); diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs index c9a6354bf97..d32828192e9 100644 --- a/src/libsyntax/print/pprust.rs +++ b/src/libsyntax/print/pprust.rs @@ -1515,6 +1515,19 @@ impl<'a> State<'a> { try!(space(&mut self.s)); try!(self.print_block(&**blk)); } + ast::ExprWhileLet(ref pat, ref expr, ref blk, opt_ident) => { + for ident in opt_ident.iter() { + try!(self.print_ident(*ident)); + try!(self.word_space(":")); + } + try!(self.head("while let")); + try!(self.print_pat(&**pat)); + try!(space(&mut self.s)); + try!(self.word_space("=")); + try!(self.print_expr(&**expr)); + try!(space(&mut self.s)); + try!(self.print_block(&**blk)); + } ast::ExprForLoop(ref pat, ref iter, ref blk, opt_ident) => { for ident in opt_ident.iter() { try!(self.print_ident(*ident)); diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs index c98c3bffcb6..00377a324a7 100644 --- a/src/libsyntax/visit.rs +++ b/src/libsyntax/visit.rs @@ -733,6 +733,11 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr) { visitor.visit_block(&**if_block); walk_expr_opt(visitor, optional_else); } + ExprWhileLet(ref pattern, ref subexpression, ref block, _) => { + visitor.visit_pat(&**pattern); + visitor.visit_expr(&**subexpression); + visitor.visit_block(&**block); + } ExprForLoop(ref pattern, ref subexpression, ref block, _) => { visitor.visit_pat(&**pattern); visitor.visit_expr(&**subexpression); diff --git a/src/test/compile-fail/lint-unnecessary-parens.rs b/src/test/compile-fail/lint-unnecessary-parens.rs index 3c962ebf216..6c766dec9a3 100644 --- a/src/test/compile-fail/lint-unnecessary-parens.rs +++ b/src/test/compile-fail/lint-unnecessary-parens.rs @@ -9,7 +9,7 @@ // except according to those terms. #![deny(unnecessary_parens)] -#![feature(if_let)] +#![feature(if_let,while_let)] #[deriving(Eq, PartialEq)] struct X { y: bool } @@ -34,6 +34,7 @@ fn main() { _ => {} } if let 1i = (1i) {} //~ ERROR unnecessary parentheses around `if let` head expression + while let 1i = (2i) {} //~ ERROR unnecessary parentheses around `while let` head expression let v = X { y: false }; // struct lits needs parens, so these shouldn't warn. if (v == X { y: true }) {} diff --git a/src/test/compile-fail/while-let.rs b/src/test/compile-fail/while-let.rs new file mode 100644 index 00000000000..0dd442ec3f6 --- /dev/null +++ b/src/test/compile-fail/while-let.rs @@ -0,0 +1,37 @@ +// Copyright 2014 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +#![feature(macro_rules,while_let)] + +fn macros() { + macro_rules! foo{ + ($p:pat, $e:expr, $b:block) => {{ + while let $p = $e $b + }} + } + macro_rules! bar{ + ($p:pat, $e:expr, $b:block) => {{ + foo!($p, $e, $b) + }} + } + + foo!(a, 1i, { //~ ERROR irrefutable while-let + println!("irrefutable pattern"); + }); + bar!(a, 1i, { //~ ERROR irrefutable while-let + println!("irrefutable pattern"); + }); +} + +pub fn main() { + while let a = 1i { //~ ERROR irrefutable while-let + println!("irrefutable pattern"); + } +} diff --git a/src/test/run-pass/while-let.rs b/src/test/run-pass/while-let.rs new file mode 100644 index 00000000000..41f54d47ad4 --- /dev/null +++ b/src/test/run-pass/while-let.rs @@ -0,0 +1,56 @@ +// Copyright 2014 The Rust Project Developers. See the COPYRIGHT +// file at the top-level directory of this distribution and at +// http://rust-lang.org/COPYRIGHT. +// +// Licensed under the Apache License, Version 2.0 or the MIT license +// , at your +// option. This file may not be copied, modified, or distributed +// except according to those terms. + +#![feature(while_let)] + +use std::collections::PriorityQueue; + +fn make_pq() -> PriorityQueue { + PriorityQueue::from_vec(vec![1i,2,3]) +} + +pub fn main() { + let mut pq = make_pq(); + let mut sum = 0i; + while let Some(x) = pq.pop() { + sum += x; + } + assert_eq!(sum, 6i); + + pq = make_pq(); + sum = 0; + 'a: while let Some(x) = pq.pop() { + sum += x; + if x == 2 { + break 'a; + } + } + assert_eq!(sum, 5i); + + pq = make_pq(); + sum = 0; + 'a: while let Some(x) = pq.pop() { + if x == 3 { + continue 'a; + } + sum += x; + } + assert_eq!(sum, 3i); + + let mut pq1 = make_pq(); + sum = 0; + while let Some(x) = pq1.pop() { + let mut pq2 = make_pq(); + while let Some(y) = pq2.pop() { + sum += x * y; + } + } + assert_eq!(sum, 6i + 12 + 18); +}