RFC: parse a' as call expression

base/exports.jl

@@ -456,6 +456,7 @@ export
     startswith,
 
 # linear algebra
+    var"'",
     adjoint,
     transpose,
     kron,

base/operators.jl

@@ -533,6 +533,8 @@ for op in (:+, :*, :&, :|, :xor, :min, :max, :kron)
     end
 end
 
+const var"'" = adjoint
+
 """
     \\(x, y)
 

base/show.jl

@@ -1336,6 +1336,16 @@ function show_unquoted(io::IO, ex::Expr, indent::Int, prec::Int, quote_level::In
                 show_unquoted(io, arg1, indent, func_prec, quote_level)
             end
 
+        # adjoint operator (i.e. "a'")
+        elseif func === :var"'" && length(func_args) == 1
+            arg1 = func_args[1]
+            if isa(arg1, Expr) || (isa(arg1, Symbol) && isoperator(arg1))
+                show_enclosed_list(io, '(', func_args, ", ", ')', indent, func_prec)
+            else
+                show_unquoted(io, arg1, indent, func_prec)
+            end
+            print(io, ''')
+
         # binary operator (i.e. "x + y")
         elseif func_prec > 0 # is a binary operator
             na = length(func_args)
@@ -1658,17 +1668,6 @@ function show_unquoted(io::IO, ex::Expr, indent::Int, prec::Int, quote_level::In
             parens && print(io, ")")
         end
 
-    # transpose
-    elseif head === Symbol('\'') && nargs == 1
-        if isa(args[1], Symbol)
-            show_unquoted(io, args[1], 0, 0, quote_level)
-        else
-            print(io, "(")
-            show_unquoted(io, args[1], 0, 0, quote_level)
-            print(io, ")")
-        end
-        print(io, head)
-
     # `where` syntax
     elseif head === :where && nargs > 1
         parens = 1 <= prec

src/julia-parser.scm

@@ -1236,7 +1236,7 @@
              (if (ts:space? s)
                  (error (string "space not allowed before \"" t "\"")))
              (take-token s)
-             (loop (list t ex)))
+             (loop (list 'call t ex)))
             ((|.'|) (error "the \".'\" operator is discontinued"))
             ((#\{ )
              (disallow-space s ex t)

test/syntax.jl

@@ -74,7 +74,7 @@ macro test999_str(args...); args; end
 @test_throws ParseError Meta.parse("sqrt(16)2")
 @test_throws ParseError Meta.parse("x' y")
 @test_throws ParseError Meta.parse("x 'y")
-@test Meta.parse("x'y") == Expr(:call, :*, Expr(Symbol("'"), :x), :y)
+@test Meta.parse("x'y") == Expr(:call, :*, Expr(:call, Symbol("'"), :x), :y)
 
 # issue #18851
 @test Meta.parse("-2[m]") == Expr(:call, :-, Expr(:ref, 2, :m))