[breaking YSH] Swap . and -> operators

New syntax:

- mydict.key
- s->startswith(prefix)

See Zulip:

    #language-design > obj->method(x) Proposal

This is #1636

spec/hay.test.sh

@@ -585,8 +585,8 @@ const children = d['children']
 write 'level 0 children' $[len(children)] ---
 
 # TODO: Do we need @[] for array expression sub?
-write 'child 0' $[children[0]->type] $[join(children[0]->args)] ---
-write 'child 1' $[children[1]->type] $[join(children[1]->args)] ---
+write 'child 0' $[children[0].type] $[join(children[0].args)] ---
+write 'child 1' $[children[1].type] $[join(children[1].args)] ---
 
 ## STDOUT:
 level 0 children

spec/ysh-assign.test.sh

@@ -187,16 +187,16 @@ x=1 y=9
 x=9 y=1
 ## END
 
-#### setvar d->key = 42 (setitem)
+#### setvar d.key = 42 (setitem)
 shopt -s oil:all
 
 var d = {}
 setvar d['f2'] = 42
-setvar d->f3 = 43
+setvar d.f3 = 43
 
 # Use the opposite thing to retrieve
 var f3 = d['f3']
-var f2 = d->f2
+var f2 = d.f2
 echo f3=$f3
 echo f2=$f2
 ## STDOUT:

spec/ysh-expr-sub.test.sh

@@ -15,10 +15,10 @@ echo $[d['key']]
 42
 ## END
 
-#### $[d->key]
+#### $[d.key]
 var d = {}
 setvar d['key'] = 42
-echo $[d->key]
+echo $[d.key]
 ## STDOUT:
 42
 ## END
@@ -30,7 +30,7 @@ var d = {}
 setvar d['key'] = 42
 echo "func $[len(a)]"
 echo "key $[d['key']]"
-echo "key $[d->key]"
+echo "key $[d.key]"
 echo "dq $[d["key"]]"
 ## STDOUT:
 func 3

spec/ysh-expr.test.sh

@@ -606,26 +606,26 @@ array=3
 comsub=6
 ## END
 
-#### obj.attr and obj.method()
+#### obj->method()
 var s = 'hi'
 
 # TODO: This does a bound method thing we probably don't want
-var s2 = s.upper()
+var s2 = s->upper()
 echo $s2
 ## STDOUT:
 HI
 ## END
 
-#### obj.method does NOT give you a bound method
+#### obj->method does NOT give you a bound method
 var s = 'hi'
-var method = s.upper
+var method = s->upper
 echo $method
-## status: 2
+## status: 3
 ## stdout-json: ""
 
-#### d->key
+#### d.key
 var d = {name: 'andy'}
-var x = d->name
+var x = d.name
 echo $x
 ## STDOUT:
 andy

spec/ysh-user-feedback.test.sh

@@ -86,7 +86,7 @@ EOF
 git-branch-merged | while read --line {
   # Note: this can't be 'const' because const is dynamic like 'readonly'.  And
   # we don't have block scope.
-  var line = _line.strip()  # removing leading space
+  var line = _line->strip()  # removing leading space
 
   # with glob: line ~~ '\**'           (awkward)
   # with regex: line ~ / %start '*' /  (not terrible, but somewhat complex)
@@ -98,7 +98,7 @@ git-branch-merged | while read --line {
   # line %startswith 'a'
   # line %endswith 'b'
 
-  if (line !== 'master' and not line.startswith('*')) {
+  if (line !== 'master' and not line->startswith('*')) {
     echo $line
   }
 } | readarray -t :branches
@@ -112,8 +112,8 @@ if (len(branches) === 0) {
 # With "append".  Hm read --lines isn't bad.
 var branches2 = %()
 git-branch-merged | while read --line {
-  var line2 = _line.strip()  # removing leading space
-  if (line2 !== 'master' and not line2.startswith('*')) {
+  var line2 = _line->strip()  # removing leading space
+  if (line2 !== 'master' and not line2->startswith('*')) {
     append :branches2 $line2
   }
 }

ysh/expr_eval.py

@@ -652,7 +652,7 @@ def EvalPlaceExpr(self, place):
                 place = cast(Attribute, UP_place)
 
                 obj = self.EvalExpr(place.obj, loc.Missing)
-                if place.op.id == Id.Expr_RArrow:
+                if place.op.id == Id.Expr_Dot:
                     attr = place.attr.tval
                     return lvalue.ObjIndex(obj, attr)
                 else:
@@ -1596,12 +1596,12 @@ def _EvalAttribute(self, node):
         # type: (Attribute) -> Any # XXX
         o = self._EvalExpr(node.obj)
         id_ = node.op.id
-        if id_ == Id.Expr_Dot:
-            # Used for .startswith()
+        if id_ == Id.Expr_RArrow:
+            # Used for s->startswith(x)
             name = node.attr.tval
             return getattr(o, name)
 
-        if id_ == Id.Expr_RArrow:  # d->key is like d['key']
+        if id_ == Id.Expr_Dot:  # d.key is like d['key']
             name = node.attr.tval
             try:
                 result = o[name]

ysh/expr_to_ast.py

@@ -580,17 +580,12 @@ def Expr(self, pnode):
                 if pnode.NumChildren() == 1:  # No trailers
                     return node
 
+                # Support a->startswith(b) and mydict.key
                 n = pnode.NumChildren()
                 i = 1
                 while i < n and ISNONTERMINAL(pnode.GetChild(i).typ):
                     node = self._Trailer(node, pnode.GetChild(i))
                     i += 1
-                if node.tag() == expr_e.Attribute:
-                    # Support a.startswith(b) but not obj.field
-                    attr_node = cast(Attribute, node)
-                    if attr_node.op.id == Id.Expr_Dot:
-                        p_die("obj.field isn't valid, but obj.method() is",
-                              attr_node.op)
 
                 if i != n:  # ['**' factor]
                     op_tok = pnode.GetChild(i).tok