require File.expand_path('../../spec_helper', __FILE__) require File.expand_path('../fixtures/precedence', __FILE__) # Specifying the behavior of operators in combination could # lead to combinatorial explosion. A better way seems to be # to use a technique from formal proofs that involve a set of # equivalent statements. Suppose you have statements A, B, C. # If they are claimed to be equivalent, this can be shown by # proving that A implies B, B implies C, and C implies A. # (Actually any closed circuit of implications.) # # Here, we can use a similar technique where we show starting # at the top that each level of operator has precedence over # the level below (as well as showing associativity within # the precedence level). =begin Excerpted from 'Programming Ruby: The Pragmatic Programmer's Guide' Second Edition by Dave Thomas, Chad Fowler, and Andy Hunt, page 324 Table 22.4. Ruby operators (high to low precedence) Method Operator Description ----------------------------------------------------------------------- :: . x* [ ] [ ]= Element reference, element set x ** Exponentiation x ! ~ + - Not, complement, unary plus and minus (method names for the last two are +@ and -@) x * / % Multiply, divide, and modulo x + - Plus and minus x >> << Right and left shift x & “And” (bitwise for integers) x ^ | Exclusive “or” and regular “or” (bitwise for integers) x <= < > >= Comparison operators x <=> == === != =~ !~ Equality and pattern match operators (!= and !~ may not be defined as methods) && Logical “and” || Logical “or” .. ... Range (inclusive and exclusive) ? : Ternary if-then-else = %= /= -= += |= &= Assignment >>= <<= *= &&= ||= **= defined? Check if symbol defined not Logical negation or and Logical composition if unless while until Expression modifiers begin/end Block expression ----------------------------------------------------------------------- * Operators marked with 'x' in the Method column are implemented as methods and can be overridden (except != and !~ as noted). (But see the specs below for implementations that define != and !~ as methods.) ** These are not included in the excerpted table but are shown here for completeness. =end # ----------------------------------------------------------------------- # It seems that this table is not correct anymore # The correct table derived from MRI's parse.y is as follows: # # Operator Assoc Description #--------------------------------------------------------------- # ! ~ + > Not, complement, unary plus # ** > Exponentiation # - > Unary minus # * / % < Multiply, divide, and modulo # + - < Plus and minus # >> << < Right and left shift # & < “And” (bitwise for integers) # ^ | < Exclusive “or” and regular “or” (bitwise for integers) # <= < > >= < Comparison operators # <=> == === != =~ !~ no Equality and pattern match operators (!= # and !~ may not be defined as methods) # && < Logical “and” # || < Logical “or” # .. ... no Range (inclusive and exclusive) # ? : > Ternary if-then-else # rescue < Rescue modifier # = %= /= -= += |= &= > Assignment # >>= <<= *= &&= ||= **= # defined? no Check if symbol defined # not > Logical negation # or and < Logical composition # if unless while until no Expression modifiers # ----------------------------------------------------------------------- # # [] and []= seem to fall out of here, as well as begin/end # # TODO: Resolve these two tables with actual specs. As the comment at the # top suggests, these specs need to be reorganized into a single describe # block for each operator. The describe block should include an example # for associativity (if relevant), an example for any short circuit behavior # (e.g. &&, ||, etc.) and an example block for each operator over which the # instant operator has immediately higher precedence. describe "Operators" do it "! ~ + is right-associative" do (!!true).should == true (~~0).should == 0 (++2).should == 2 end it "** is right-associative" do (2**2**3).should == 256 end it "** has higher precedence than unary minus" do (-2**2).should == -4 end it "unary minus is right-associative" do (--2).should == 2 end it "unary minus has higher precedence than * / %" do class UnaryMinusTest; def -@; 50; end; end b = UnaryMinusTest.new (-b * 5).should == 250 (-b / 5).should == 10 (-b % 7).should == 1 end it "treats +/- as a regular send if the arguments are known locals or block locals" do a = PrecedenceSpecs::NonUnaryOpTest.new a.add_num(1).should == [3] a.sub_num(1).should == [1] a.add_str.should == ['11'] a.add_var.should == [2] end it "* / % are left-associative" do (2*1/2).should == (2*1)/2 # Guard against the Mathn library # TODO: Make these specs not rely on specific behaviour / result values # by using mocks. conflicts_with :Prime do (2*1/2).should_not == 2*(1/2) end (10/7/5).should == (10/7)/5 (10/7/5).should_not == 10/(7/5) (101 % 55 % 7).should == (101 % 55) % 7 (101 % 55 % 7).should_not == 101 % (55 % 7) (50*20/7%42).should == ((50*20)/7)%42 (50*20/7%42).should_not == 50*(20/(7%42)) end it "* / % have higher precedence than + -" do (2+2*2).should == 6 (1+10/5).should == 3 (2+10%5).should == 2 (2-2*2).should == -2 (1-10/5).should == -1 (10-10%4).should == 8 end it "+ - are left-associative" do (2-3-4).should == -5 (4-3+2).should == 3 binary_plus = Class.new(String) do alias_method :plus, :+ def +(a) plus(a) + "!" end end s = binary_plus.new("a") (s+s+s).should == (s+s)+s (s+s+s).should_not == s+(s+s) end it "+ - have higher precedence than >> <<" do (2<<1+2).should == 16 (8>>1+2).should == 1 (4<<1-3).should == 1 (2>>1-3).should == 8 end it ">> << are left-associative" do (1 << 2 << 3).should == 32 (10 >> 1 >> 1).should == 2 (10 << 4 >> 1).should == 80 end it ">> << have higher precedence than &" do (4 & 2 << 1).should == 4 (2 & 4 >> 1).should == 2 end it "& is left-associative" do class BitwiseAndTest; def &(a); a+1; end; end c = BitwiseAndTest.new (c & 5 & 2).should == (c & 5) & 2 (c & 5 & 2).should_not == c & (5 & 2) end it "& has higher precedence than ^ |" do (8 ^ 16 & 16).should == 24 (8 | 16 & 16).should == 24 end it "^ | are left-associative" do class OrAndXorTest; def ^(a); a+10; end; def |(a); a-10; end; end d = OrAndXorTest.new (d ^ 13 ^ 16).should == (d ^ 13) ^ 16 (d ^ 13 ^ 16).should_not == d ^ (13 ^ 16) (d | 13 | 4).should == (d | 13) | 4 (d | 13 | 4).should_not == d | (13 | 4) end it "^ | have higher precedence than <= < > >=" do (10 <= 7 ^ 7).should == false (10 < 7 ^ 7).should == false (10 > 7 ^ 7).should == true (10 >= 7 ^ 7).should == true (10 <= 7 | 7).should == false (10 < 7 | 7).should == false (10 > 7 | 7).should == true (10 >= 7 | 7).should == true end it "<= < > >= are left-associative" do class ComparisonTest def <=(a); 0; end; def <(a); 0; end; def >(a); 0; end; def >=(a); 0; end; end e = ComparisonTest.new (e <= 0 <= 1).should == (e <= 0) <= 1 (e <= 0 <= 1).should_not == e <= (0 <= 1) (e < 0 < 1).should == (e < 0) < 1 (e < 0 < 1).should_not == e < (0 < 1) (e >= 0 >= 1).should == (e >= 0) >= 1 (e >= 0 >= 1).should_not == e >= (0 >= 1) (e > 0 > 1).should == (e > 0) > 1 (e > 0 > 1).should_not == e > (0 > 1) end it "<=> == === != =~ !~ are non-associative" do lambda { eval("1 <=> 2 <=> 3") }.should raise_error(SyntaxError) lambda { eval("1 == 2 == 3") }.should raise_error(SyntaxError) lambda { eval("1 === 2 === 3") }.should raise_error(SyntaxError) lambda { eval("1 != 2 != 3") }.should raise_error(SyntaxError) lambda { eval("1 =~ 2 =~ 3") }.should raise_error(SyntaxError) lambda { eval("1 !~ 2 !~ 3") }.should raise_error(SyntaxError) end it "<=> == === != =~ !~ have higher precedence than &&" do (false && 2 <=> 3).should == false (false && 3 == false).should == false (false && 3 === false).should == false (false && 3 != true).should == false class FalseClass; def =~(o); o == false; end; end (false && true =~ false).should == (false && (true =~ false)) (false && true =~ false).should_not == ((false && true) =~ false) class FalseClass; undef_method :=~; end (false && true !~ true).should == false end # XXX: figure out how to test it # (a && b) && c equals to a && (b && c) for all a,b,c values I can imagine so far it "&& is left-associative" it "&& has higher precedence than ||" do (true || false && false).should == true end # XXX: figure out how to test it it "|| is left-associative" it "|| has higher precedence than .. ..." do (1..false||10).should == (1..10) (1...false||10).should == (1...10) end it ".. ... are non-associative" do lambda { eval("1..2..3") }.should raise_error(SyntaxError) lambda { eval("1...2...3") }.should raise_error(SyntaxError) end # XXX: this is commented now due to a bug in compiler, which cannot # distinguish between range and flip-flop operator so far. zenspider is # currently working on a new lexer, which will be able to do that. # As soon as it's done, these piece should be reenabled. # # it ".. ... have higher precedence than ? :" do # (1..2 ? 3 : 4).should == 3 # (1...2 ? 3 : 4).should == 3 # end it "? : is right-associative" do (true ? 2 : 3 ? 4 : 5).should == 2 end def oops; raise end it "? : has higher precedence than rescue" do (true ? oops : 0 rescue 10).should == 10 end # XXX: figure how to test it (problem similar to || associativity) it "rescue is left-associative" it "rescue has higher precedence than =" do a = oops rescue 10 a.should == 10 # rescue doesn't have the same sense for %= /= and friends end it "= %= /= -= += |= &= >>= <<= *= &&= ||= **= are right-associative" do a = b = 10 a.should == 10 b.should == 10 a = b = 10 a %= b %= 3 a.should == 0 b.should == 1 a = b = 10 a /= b /= 2 a.should == 2 b.should == 5 a = b = 10 a -= b -= 2 a.should == 2 b.should == 8 a = b = 10 a += b += 2 a.should == 22 b.should == 12 a,b = 32,64 a |= b |= 2 a.should == 98 b.should == 66 a,b = 25,13 a &= b &= 7 a.should == 1 b.should == 5 a,b=8,2 a >>= b >>= 1 a.should == 4 b.should == 1 a,b=8,2 a <<= b <<= 1 a.should == 128 b.should == 4 a,b=8,2 a *= b *= 2 a.should == 32 b.should == 4 a,b=10,20 a &&= b &&= false a.should == false b.should == false a,b=nil,nil a ||= b ||= 10 a.should == 10 b.should == 10 a,b=2,3 a **= b **= 2 a.should == 512 b.should == 9 end it "= %= /= -= += |= &= >>= <<= *= &&= ||= **= have higher precedence than defined? operator" do (defined? a = 10).should == "assignment" (defined? a %= 10).should == "assignment" (defined? a /= 10).should == "assignment" (defined? a -= 10).should == "assignment" (defined? a += 10).should == "assignment" (defined? a |= 10).should == "assignment" (defined? a &= 10).should == "assignment" (defined? a >>= 10).should == "assignment" (defined? a <<= 10).should == "assignment" (defined? a *= 10).should == "assignment" (defined? a &&= 10).should == "assignment" (defined? a ||= 10).should == "assignment" (defined? a **= 10).should == "assignment" end # XXX: figure out how to test it it "defined? is non-associative" it "defined? has higher precedence than not" do # does it have sense? (not defined? qqq).should == true end it "not is right-associative" do (not not false).should == false (not not 10).should == true end it "not has higher precedence than or/and" do (not false and false).should == false (not false or true).should == true end # XXX: figure out how to test it it "or/and are left-associative" it "or/and have higher precedence than if unless while until modifiers" do (1 if 2 and 3).should == 1 (1 if 2 or 3).should == 1 (1 unless false and true).should == 1 (1 unless false or false).should == 1 (1 while true and false).should == nil # would hang upon error (1 while false or false).should == nil ((raise until true and false) rescue 10).should == 10 (1 until false or true).should == nil # would hang upon error end # XXX: it seems to me they are right-associative it "if unless while until are non-associative" end