Arithmetic evaluation: Difference between revisions

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     $_ = ev_ast($_) foreach @operands;
     return $ops{$op}->(@operands);}}</lang>
+=={{header|Perl 6}}==
+{{works with|Rakudo|#22 "Thousand Oaks"}}
+<lang perl6>sub ev (Str $s --> Num) {
+    grammar expr {
+        token TOP { ^ <sum> $ }
+        token sum { <product> (('+' || '-') <product>)* }
+        token product { <factor> (('*' || '/') <factor>)* }
+        token factor { <unary_minus>? [ <parens> || <literal> ] }
+        token unary_minus { '-' }
+        token parens { '(' <sum> ')' }
+        token literal { \d+ ['.' \d+]? || '.' \d+ }
+    }
+    my sub minus ($b) { $b ?? -1 !! +1 }
+    my sub sum ($x) {
+        [+] product($x<product>), map
+            { minus($^y[0] eq '-') * product $^y<product> },
+            |($x[0] or [])
+    }
+    my sub product ($x) {
+        [*] factor($x<factor>), map
+            { factor($^y<factor>) ** minus($^y[0] eq '/') },
+            |($x[0] or [])
+    }
+    my sub factor ($x) {
+        minus($x<unary_minus>) * ($x<parens>
+          ?? sum $x<parens><sum>
+          !! $x<literal>)
+    }
+    expr.parse([~] split /\s+/, $s);
+    $/ or fail 'No parse.';
+    sum $/<sum>;
+}</lang>
+Testing:
+<lang perl6>say ev '5';                                    #   5
+say ev '1 + 2 - 3 * 4 / 5';                    #   0.6
+say ev '1 + 5*3.4 - .5  -4 / -2 * (3+4) -6';   #  25.5
+say ev '((11+15)*15)* 2 + (3) * -4 *1';        # 768</lang>
 =={{header|Pop11}}==