From 6e5ce1843563ea52c8a22913b44f8740c15a7905 Mon Sep 17 00:00:00 2001
From: Aidan <46799759+PossiblyAShrub@users.noreply.github.com>
Date: Thu, 24 Oct 2024 19:11:29 -0600
Subject: [PATCH] [ysh breaking] 1 .. 5 range replaced with 1..<5 half open and
 1..=5 closed range (#2102)

This is issue #2096
---
 display/pp_value.py          |  2 +-
 doc/error-catalog.md         | 26 +++++++++++++++++++++++
 doc/ref/chap-expr-lang.md    | 14 +++++++-----
 doc/ref/toc-ysh.md           |  2 +-
 doc/ysh-tour.md              |  4 ++--
 frontend/id_kind_def.py      |  5 +++--
 frontend/lexer_def.py        | 10 +++++----
 spec/ysh-bugs.test.sh        |  8 +++----
 spec/ysh-builtins.test.sh    |  2 +-
 spec/ysh-closures.test.sh    |  6 +++---
 spec/ysh-convert.test.sh     |  4 ++--
 spec/ysh-for.test.sh         |  2 +-
 spec/ysh-func.test.sh        |  2 +-
 spec/ysh-int-float.test.sh   |  2 +-
 spec/ysh-json.test.sh        |  4 ++--
 spec/ysh-list.test.sh        | 10 ++++-----
 spec/ysh-methods.test.sh     |  2 +-
 spec/ysh-printing.test.sh    |  8 +++----
 spec/ysh-regex-api.test.sh   |  2 +-
 spec/ysh-slice-range.test.sh | 41 ++++++++++++++++++++++++------------
 spec/ysh-word-eval.test.sh   |  2 +-
 stdlib/ysh/list-test.ysh     |  6 +++---
 stdlib/ysh/list.ysh          |  4 ++--
 stdlib/ysh/math.ysh          |  2 +-
 test/ysh-parse-errors.sh     |  6 ++++++
 test/ysh-runtime-errors.sh   |  6 +++---
 ysh/expr_eval.py             |  3 +++
 ysh/expr_parse.py            |  4 ++++
 ysh/grammar.pgen2            |  5 ++++-
 ysh/grammar_gen.py           |  3 ++-
 30 files changed, 130 insertions(+), 67 deletions(-)

diff --git a/display/pp_value.py b/display/pp_value.py
index f4bf01eef..aead5eaf2 100644
--- a/display/pp_value.py
+++ b/display/pp_value.py
@@ -412,7 +412,7 @@ def _Value(self, val):
             elif case(value_e.Range):
                 r = cast(value.Range, val)
                 type_name = self._Styled(self.type_style, UText(ValType(r)))
-                mdocs = [UText(str(r.lower)), UText(".."), UText(str(r.upper))]
+                mdocs = [UText(str(r.lower)), UText("..<"), UText(str(r.upper))]
                 return self._SurroundedAndPrefixed("(", type_name, " ",
                                                    self._Join(mdocs, "", " "),
                                                    ")")
diff --git a/doc/error-catalog.md b/doc/error-catalog.md
index cbadb9107..dabf2d4bb 100644
--- a/doc/error-catalog.md
+++ b/doc/error-catalog.md
@@ -207,6 +207,32 @@ standard boolean operators are written as `a and b`, `a or b` and `not a`.
 This differs from [command mode](command-vs-expression-mode.html) which uses
 shell-like `||` for "OR", `&&` for "AND" and `!` for "NOT".
 
+### OILS-ERR-16
+
+```
+  for x in (1 .. 5) {
+              ^~
+[ -c flag ]:1: Use ..< for half-open range, or ..= for closed range (OILS-ERR-16)
+```
+
+There are two ways to construct a [Range](ref/chap-expr-lang#range). The `..<`
+operator is for half-open ranges and the `..=` operator is for closed ranges:
+
+    for i in (0 ..< 3) {
+      echo $i
+    }
+    => 0
+    => 1
+    => 2
+
+    for i in (0 ..= 3) {
+      echo $i
+    }
+    => 0
+    => 1
+    => 2
+    => 3
+
 ## Runtime Errors - Traditional Shell
 
 These errors may occur in shells like [bash]($xref) and [zsh]($xref).
diff --git a/doc/ref/chap-expr-lang.md b/doc/ref/chap-expr-lang.md
index 5b29c2833..ed90a5cfb 100644
--- a/doc/ref/chap-expr-lang.md
+++ b/doc/ref/chap-expr-lang.md
@@ -231,21 +231,25 @@ the same name:
 
 ### range
 
-A range is a sequence of numbers that can be iterated over:
+A Range is a sequence of numbers that can be iterated over. The `..<` operator
+constructs half-open ranges.
 
-    for i in (0 .. 3) {
+    for i in (0 ..< 3) {
       echo $i
     }
     => 0
     => 1
     => 2
 
-As with slices, the last number isn't included.  To iterate from 1 to n, you
-can use this idiom:
+The `..=` operator constructs closed ranges:
 
-    for i in (1 .. n+1) {
+    for i in (0 ..= 3) {
       echo $i
     }
+    => 0
+    => 1
+    => 2
+    => 3
 
 ### block-expr
 
diff --git a/doc/ref/toc-ysh.md b/doc/ref/toc-ysh.md
index 1afca9767..424dccf59 100644
--- a/doc/ref/toc-ysh.md
+++ b/doc/ref/toc-ysh.md
@@ -262,7 +262,7 @@ X [External Lang] BEGIN   END   when (awk)
                   str-template  ^"$a and $b" for Str::replace()
                   list-literal  ['one', 'two', 3]  :| unquoted words |
                   dict-literal  {name: 'bob'}  {a, b}
-                  range         1 .. n+1
+                  range         1 ..< n  1 ..= n
                   block-expr    ^(echo $PWD)
                   expr-literal  ^[1 + 2*3]
                 X expr-sub      $[myobj]
diff --git a/doc/ysh-tour.md b/doc/ysh-tour.md
index 326236067..0347f729e 100644
--- a/doc/ysh-tour.md
+++ b/doc/ysh-tour.md
@@ -453,7 +453,7 @@ Ask for the loop index:
 To iterate over a typed data, use parentheses around an **expression**.  The
 expression should evaluate to an integer `Range`, `List`, or `Dict`:
 
-    for i in (3 .. 5) {  # range operator ..
+    for i in (3 ..< 5) {  # range operator ..<
       echo "i = $i"
     }
     # =>
@@ -740,7 +740,7 @@ Here's a pure function:
 
     func myRepeat(s, n; special=false) {  # positional; named params
       var parts = []
-      for i in (0 .. n) {
+      for i in (0 ..< n) {
         append $s (parts)
       }
       var result = join(parts)
diff --git a/frontend/id_kind_def.py b/frontend/id_kind_def.py
index 1d87fb6fd..22e5e3f1f 100755
--- a/frontend/id_kind_def.py
+++ b/frontend/id_kind_def.py
@@ -232,7 +232,7 @@ def AddKinds(spec):
     #   $'\z'  Such bad codes are accepted when parse_backslash is on
     #          (default in OSH), so we have to lex them.
     #  (x == y) should used === or ~==
-    spec.AddKind('Unknown', ['Tok', 'Backslash', 'DEqual', 'DAmp', 'DPipe'])
+    spec.AddKind('Unknown', ['Tok', 'Backslash', 'DEqual', 'DAmp', 'DPipe', 'DDot'])
 
     spec.AddKind('Eol', ['Tok'])  # no more tokens on line (\0)
 
@@ -333,7 +333,8 @@ def AddKinds(spec):
             'Float',
             'Bang',  # eggex !digit, ![a-z]
             'Dot',
-            'DDot',
+            'DDotLessThan',
+            'DDotEqual',
             'Colon',  # mylist:pop()
             'RArrow',
             'RDArrow',
diff --git a/frontend/lexer_def.py b/frontend/lexer_def.py
index 0cc0b6123..fc4e875aa 100644
--- a/frontend/lexer_def.py
+++ b/frontend/lexer_def.py
@@ -1103,10 +1103,12 @@ def R(pat, tok_type):
     C('//', Id.Expr_DSlash),  # For YSH integer division
     C('~==', Id.Expr_TildeDEqual),  # approximate equality
 
-    C('.', Id.Expr_Dot),      # d.key is alias for d['key']
-    C('..', Id.Expr_DDot),    # range 1..5
-    C('->', Id.Expr_RArrow),  # s->startswith()
-    C('$', Id.Expr_Dollar),   # legacy regex end: /d+ $/ (better written /d+ >/
+    C('.', Id.Expr_Dot),             # d.key is alias for d['key']
+    C('..', Id.Unknown_DDot),        # legacy half-open range 1..5
+    C('..<', Id.Expr_DDotLessThan),  # half-open range 1..<5
+    C('..=', Id.Expr_DDotEqual),     # closed range 1..5
+    C('->', Id.Expr_RArrow),         # s->startswith()
+    C('$', Id.Expr_Dollar),          # legacy regex end: /d+ $/ (better written /d+ >/
 
     # Reserved this.  Go uses it for channels, etc.
     # I guess it conflicts with -4<-3, but that's OK -- spaces suffices.
diff --git a/spec/ysh-bugs.test.sh b/spec/ysh-bugs.test.sh
index 2227d038f..ce8712d5b 100644
--- a/spec/ysh-bugs.test.sh
+++ b/spec/ysh-bugs.test.sh
@@ -142,7 +142,7 @@ pp test_ (pipe())
 #### shvar then replace - bug #1986 context manager crash
 
 shvar FOO=bar {
-  for x in (1 .. 500) {
+  for x in (1 ..< 500) {
     var Q = "hello"
     setvar Q = Q=>replace("hello","world")
   }
@@ -239,20 +239,20 @@ case (WEIGHT) {
 
 proc p {
   var s = "hi"
-  for q in (1..50) {
+  for q in (1..<50) {
     shvar Q="whatever" {
       setvar s = "." ++ s
     }
   }
 }
 
-for i in (1..10) {
+for i in (1..<10) {
   p
 }
 
 if false {
   echo 'testing for longer'
-  for i in (1 .. 1000) {
+  for i in (1 ..< 1000) {
     p
   }
 }
diff --git a/spec/ysh-builtins.test.sh b/spec/ysh-builtins.test.sh
index 1fbfc32b6..cb03b5ee5 100644
--- a/spec/ysh-builtins.test.sh
+++ b/spec/ysh-builtins.test.sh
@@ -638,7 +638,7 @@ echo $[type(f)]
 echo $[type(len)]
 echo $[type('foo'=>startsWith)]
 echo $[type('foo'=>join)]  # Type error happens later
-echo $[type(1..3)]
+echo $[type(1..<3)]
 ## STDOUT:
 Int
 Str
diff --git a/spec/ysh-closures.test.sh b/spec/ysh-closures.test.sh
index 4e37bd4cc..ec88cd211 100644
--- a/spec/ysh-closures.test.sh
+++ b/spec/ysh-closures.test.sh
@@ -50,7 +50,7 @@ proc task (; tasks, expr) {
 func makeTasks() {
   var tasks = []
   var x = 'x'
-  for __hack__ in (0 .. 3) {
+  for __hack__ in (0 ..< 3) {
     var i = __hack__
     var j = i + 2
     task (tasks, ^"$x: i = $i, j = $j")
@@ -82,7 +82,7 @@ proc task (; tasks; ; b) {
 func makeTasks() {
   var tasks = []
   var x = 'x'
-  for __hack__ in (0 .. 3) {
+  for __hack__ in (0 ..< 3) {
     var i = __hack__
     var j = i + 2
     task (tasks) { echo "$x: i = $i, j = $j" }
@@ -108,7 +108,7 @@ x: i = 2, j = 4
 shopt --set ysh:upgrade
 
 var procs = []
-for i in (0 .. 3) {
+for i in (0 ..< 3) {
   proc __invoke__ (; self) {
     echo "i = $[self.i]"
   }
diff --git a/spec/ysh-convert.test.sh b/spec/ysh-convert.test.sh
index 9e102c9f8..145b4bf60 100644
--- a/spec/ysh-convert.test.sh
+++ b/spec/ysh-convert.test.sh
@@ -9,7 +9,7 @@ echo "$[bool({})]"
 echo "$[bool(null)]"
 echo "$[bool(len)]"
 echo "$[bool('foo'=>startsWith)]"
-echo "$[bool(1..3)]"
+echo "$[bool(1..<3)]"
 ## STDOUT:
 true
 false
@@ -180,7 +180,7 @@ foo
 #### list() from range
 shopt -s ysh:upgrade
 
-var mylist = list(0..3)
+var mylist = list(0..<3)
 write @mylist
 ## STDOUT:
 0
diff --git a/spec/ysh-for.test.sh b/spec/ysh-for.test.sh
index dd6d77d71..0a57f58ea 100644
--- a/spec/ysh-for.test.sh
+++ b/spec/ysh-for.test.sh
@@ -33,7 +33,7 @@ key age
 
 
 #### For loop over range
-var myrange = 0 .. 3
+var myrange = 0 ..< 3
 for i in (myrange) {
   echo "i $i"
 }
diff --git a/spec/ysh-func.test.sh b/spec/ysh-func.test.sh
index 53c9c9c9f..ffafc6458 100644
--- a/spec/ysh-func.test.sh
+++ b/spec/ysh-func.test.sh
@@ -250,7 +250,7 @@ var cache = []
 var maxSize = 4
 
 func remove(l, i) {
-  for i in (i .. len(l) - 1) {
+  for i in (i ..< len(l) - 1) {
     setvar l[i] = l[i + 1]
   }
 
diff --git a/spec/ysh-int-float.test.sh b/spec/ysh-int-float.test.sh
index 6e06e2ad9..92453e586 100644
--- a/spec/ysh-int-float.test.sh
+++ b/spec/ysh-int-float.test.sh
@@ -80,7 +80,7 @@ shopt -s ysh:upgrade
 # 1e-324 == 0.0 in Python
 
 var zeros = []
-for i in (1 .. 324) {
+for i in (1 ..< 324) {
   call zeros->append('0')
 }
 
diff --git a/spec/ysh-json.test.sh b/spec/ysh-json.test.sh
index 08b60c13f..26c7daa41 100644
--- a/spec/ysh-json.test.sh
+++ b/spec/ysh-json.test.sh
@@ -1168,10 +1168,10 @@ shopt -s ysh:upgrade
 proc pairs(n) {
   var m = int(n)  # TODO: 1 .. n should auto-convert?
 
-  for i in (1 .. m) {
+  for i in (1 ..< m) {
     write -n -- '['
   }
-  for i in (1 .. m) {
+  for i in (1 ..< m) {
     write -n -- ']'
   }
 }
diff --git a/spec/ysh-list.test.sh b/spec/ysh-list.test.sh
index bf985a01e..299b61dee 100644
--- a/spec/ysh-list.test.sh
+++ b/spec/ysh-list.test.sh
@@ -140,9 +140,9 @@ echo -$x-  # fails with type error
 ## END
 
 #### List->extend()
-var l = list(1..3)
+var l = list(1..<3)
 echo $[len(l)]
-call l->extend(list(3..6))
+call l->extend(list(3..<6))
 echo $[len(l)]
 ## STDOUT:
 2
@@ -151,9 +151,9 @@ echo $[len(l)]
 
 #### List append()/extend() should return null
 shopt -s ysh:all
-var l = list(1..3)
+var l = list(1..<3)
 
-var result = l->extend(list(3..6))
+var result = l->extend(list(3..<6))
 assert [null === result]
 
 setvar result = l->append(6)
@@ -166,7 +166,7 @@ pass
 
 #### List pop()
 shopt -s ysh:all
-var l = list(1..5)
+var l = list(1..<5)
 assert [4 === l->pop()]
 assert [3 === l->pop()]
 assert [2 === l->pop()]
diff --git a/spec/ysh-methods.test.sh b/spec/ysh-methods.test.sh
index 291f67121..5db754d15 100644
--- a/spec/ysh-methods.test.sh
+++ b/spec/ysh-methods.test.sh
@@ -584,7 +584,7 @@ pp test_ (c)
 ## END
 
 #### List->reverse() from iterator
-var x = list(0 .. 3)
+var x = list(0 ..< 3)
 call x->reverse()
 write @x
 ## STDOUT:
diff --git a/spec/ysh-printing.test.sh b/spec/ysh-printing.test.sh
index cc866baa4..322b818c2 100644
--- a/spec/ysh-printing.test.sh
+++ b/spec/ysh-printing.test.sh
@@ -35,11 +35,11 @@
 ## END
 
 #### Range
-var x = 1..100
+var x = 1..<100
 
 pp value (x)
 
-# TODO: show type here, like (Range 1 .. 100)
+# TODO: show type here, like (Range 1 ..< 100)
 
 pp value ({k: x})
 
@@ -49,8 +49,8 @@ pp test_ (x)
 pp test_ ({k: x})
 
 ## STDOUT:
-(Range 1 .. 100)
-(Dict)  {k: (Range 1 .. 100)}
+(Range 1 ..< 100)
+(Dict)  {k: (Range 1 ..< 100)}
 
 <Range>
 (Dict)   {"k":<Range>}
diff --git a/spec/ysh-regex-api.test.sh b/spec/ysh-regex-api.test.sh
index 25a0c81d7..c149eb056 100644
--- a/spec/ysh-regex-api.test.sh
+++ b/spec/ysh-regex-api.test.sh
@@ -752,7 +752,7 @@ shopt --set ysh:all
 
 var mystr = '1abc2abc3abc'
 
-for count in (-2..4) {
+for count in (-2..<4) {
   write $[mystr.replace('abc', "-", count=count)]
   write $[mystr.replace('abc', ^"-", count=count)]
   write $[mystr.replace(/ [a-z]+ /, "-", count=count)]
diff --git a/spec/ysh-slice-range.test.sh b/spec/ysh-slice-range.test.sh
index fb810a967..d2ed0c836 100644
--- a/spec/ysh-slice-range.test.sh
+++ b/spec/ysh-slice-range.test.sh
@@ -14,16 +14,16 @@
 # >>> xrange(1,3)  < xrange(1,4)
 # True
 
-= 1..3
+= 1..<3
 
 ## STDOUT:
-(Range 1 .. 3)
+(Range 1 ..< 3)
 ## END
 
 #### precedence of 1:3 vs bitwise operator
-= 3..3|4
+= 3..<3|4
 ## STDOUT:
-(Range 3 .. 7)
+(Range 3 ..< 7)
 ## END
 
 #### subscript and slice :| 1 2 3 4 |
@@ -57,20 +57,20 @@ out of bounds
 
 #### Range end points can be int-looking Strings
 
-pp test_ (list('3' .. '6'))
+pp test_ (list('3' ..< '6'))
 
 var i = '5'
 
-pp test_ (list(i .. 7))
-pp test_ (list(3 .. i))
+pp test_ (list(i ..< 7))
+pp test_ (list(3 ..< i))
 
 var i = '-5'
 
-pp test_ (list(i .. -3))
-pp test_ (list(-7 .. i))
+pp test_ (list(i ..< -3))
+pp test_ (list(-7 ..< i))
 
 # Not allowed
-pp test_ ('a' .. 'z')
+pp test_ ('a' ..< 'z')
 
 ## status: 3
 ## STDOUT:
@@ -83,7 +83,7 @@ pp test_ ('a' .. 'z')
 
 #### Slice indices can be int-looking strings
 
-var a = list(0..10)
+var a = list(0..<10)
 #pp test_ (a)
 
 pp test_ (a['3': '6'])
@@ -215,10 +215,10 @@ pp test_ (b)
 ## END
 
 #### Iterate over range
-for i in (1..5) {
+for i in (1..<5) {
     echo $[i]
 }
-for i, n in (1..4) {
+for i, n in (1..<4) {
     echo "$[i], $[n]"
 }
 ## STDOUT:
@@ -234,7 +234,7 @@ for i, n in (1..4) {
 #### Loops over bogus ranges terminate
 # Regression test for bug found during dev. Loops over backwards ranges should
 # terminate immediately.
-for i in (5..1) {
+for i in (5..<1) {
     echo $[i]
 }
 ## STDOUT:
@@ -263,3 +263,16 @@ var t3 = mytable[:2, %(name age)]
 (Str)   'TODO: Table Slicing'
 (Str)   'TODO: Table Slicing'
 ## END
+
+#### Closed ranges
+
+for x in (1..=2) {
+  echo $x
+}
+
+= 1..=2
+## STDOUT:
+1
+2
+(Range 1 ..< 3)
+## END
diff --git a/spec/ysh-word-eval.test.sh b/spec/ysh-word-eval.test.sh
index f124c20ac..cf8dd4358 100644
--- a/spec/ysh-word-eval.test.sh
+++ b/spec/ysh-word-eval.test.sh
@@ -104,7 +104,7 @@ true
 
 #### Wrong sigil with $range() is runtime error
 shopt -s ysh:upgrade
-echo $[10 .. 15]
+echo $[10 ..< 15]
 echo 'should not get here'
 ## status: 3
 ## STDOUT:
diff --git a/stdlib/ysh/list-test.ysh b/stdlib/ysh/list-test.ysh
index 4fc08bec8..8aff90bb6 100755
--- a/stdlib/ysh/list-test.ysh
+++ b/stdlib/ysh/list-test.ysh
@@ -45,9 +45,9 @@ proc test-sum {
   assert [0 === sum([0])]
   assert [6 === sum([1, 2, 3])]
 
-  assert [3 === sum( 0 .. 3 )]
-  assert [45 === sum( 0 .. 3; start=42)]
-  assert [42 === sum( 0 .. 0, start=42)]
+  assert [3 === sum( 0 ..< 3 )]
+  assert [45 === sum( 0 ..< 3; start=42)]
+  assert [42 === sum( 0 ..< 0, start=42)]
 }
 
 proc test-repeat-str {
diff --git a/stdlib/ysh/list.ysh b/stdlib/ysh/list.ysh
index bfb84586b..5ce8ba251 100644
--- a/stdlib/ysh/list.ysh
+++ b/stdlib/ysh/list.ysh
@@ -45,14 +45,14 @@ func repeat(x, n) {
   case (t) {
     Str {
       var parts = []
-      for i in (0 .. n) {
+      for i in (0 ..< n) {
         call parts->append(x)
       }
       return (join(parts))
     }
     List {
       var result = []
-      for i in (0 .. n) {
+      for i in (0 ..< n) {
         call result->extend(x)
       }
       return (result)
diff --git a/stdlib/ysh/math.ysh b/stdlib/ysh/math.ysh
index 4cd28fb71..189a62a8e 100644
--- a/stdlib/ysh/math.ysh
+++ b/stdlib/ysh/math.ysh
@@ -20,7 +20,7 @@ func __math_select(list, cmp) {
   }
 
   var match = list[0]
-  for i in (1 .. len(list)) {
+  for i in (1 ..< len(list)) {
     setvar match = cmp(list[i], match)
   }
   return (match)
diff --git a/test/ysh-parse-errors.sh b/test/ysh-parse-errors.sh
index 88c8f4216..cf0f1ffbc 100755
--- a/test/ysh-parse-errors.sh
+++ b/test/ysh-parse-errors.sh
@@ -1690,6 +1690,12 @@ test-unknown-boolops() {
   _osh-parse-error '= !a'
 }
 
+test-expr-range() {
+  _osh-parse-error '= 1..5'
+  _osh-should-parse '= 1..<5'
+  _osh-should-parse '= 1..=5'
+}
+
 #
 # Entry Points
 #
diff --git a/test/ysh-runtime-errors.sh b/test/ysh-runtime-errors.sh
index 5cca8c4a3..0d04c33a3 100755
--- a/test/ysh-runtime-errors.sh
+++ b/test/ysh-runtime-errors.sh
@@ -991,10 +991,10 @@ test-assert() {
   _ysh-expr-error 'assert [null === 42]'
 
   # One is long
-  _ysh-expr-error 'assert [null === list(1 .. 50)]'
+  _ysh-expr-error 'assert [null === list(1 ..< 50)]'
 
   # Both are long
-  _ysh-expr-error 'assert [{k: list(3 .. 40)} === list(1 .. 50)]'
+  _ysh-expr-error 'assert [{k: list(3 ..< 40)} === list(1 ..< 50)]'
 }
 
 test-pp() {
@@ -1013,7 +1013,7 @@ var x = 42;
 pp [x]'
 
   _ysh-should-run '
-var x = list(1 .. 50);
+var x = list(1 ..< 50);
 pp [x]'
 }
 
diff --git a/ysh/expr_eval.py b/ysh/expr_eval.py
index 181060cff..4f8489b77 100644
--- a/ysh/expr_eval.py
+++ b/ysh/expr_eval.py
@@ -1280,6 +1280,9 @@ def _EvalExpr(self, node):
                 i2 = _ConvertToInt(self._EvalExpr(node.upper),
                                    'Range end should be Int', node.op)
 
+                if node.op.id == Id.Expr_DDotEqual:  # Closed range
+                    i2 = mops.Add(i2, mops.ONE)
+
                 # TODO: Don't truncate
                 return value.Range(mops.BigTruncate(i1), mops.BigTruncate(i2))
 
diff --git a/ysh/expr_parse.py b/ysh/expr_parse.py
index 2afb3308d..496d56690 100644
--- a/ysh/expr_parse.py
+++ b/ysh/expr_parse.py
@@ -79,12 +79,16 @@ def _Classify(gr, tok):
 
     if id_ == Id.Unknown_DEqual:
         p_die('Use === to be exact, or ~== to convert types', tok)
+
     if id_ == Id.Unknown_DAmp:
         p_die("Use 'and' in expression mode (OILS-ERR-15)", tok)
     if id_ == Id.Unknown_DPipe:
         p_die("Use 'or' in expression mode (OILS-ERR-15)", tok)
     # Not possible to check '!' as it conflicts with Id.Expr_Bang
 
+    if id_ == Id.Unknown_DDot:
+        p_die('Use ..< for half-open range, or ..= for closed range (OILS-ERR-16)', tok)
+
     if id_ == Id.Unknown_Tok:
         type_str = ''
     else:
diff --git a/ysh/grammar.pgen2 b/ysh/grammar.pgen2
index a07d8957d..d38cf157e 100644
--- a/ysh/grammar.pgen2
+++ b/ysh/grammar.pgen2
@@ -54,7 +54,10 @@ not_test: 'not' not_test | comparison
 comparison: range_expr (comp_op range_expr)*
 
 # Unlike slice, beginning and end are required
-range_expr: expr ['..' expr]
+range_expr: (
+  expr ['..<' expr] |
+  expr ['..=' expr]
+)
 
 # YSH patch: remove legacy <>, add === and more
 comp_op: (
diff --git a/ysh/grammar_gen.py b/ysh/grammar_gen.py
index 781cdd272..a8a817de5 100755
--- a/ysh/grammar_gen.py
+++ b/ysh/grammar_gen.py
@@ -75,7 +75,8 @@ def main(argv):
     OPS = {
         '!': Id.Expr_Bang,
         '.': Id.Expr_Dot,
-        '..': Id.Expr_DDot,
+        '..=': Id.Expr_DDotEqual,
+        '..<': Id.Expr_DDotLessThan,
         '->': Id.Expr_RArrow,
         '=>': Id.Expr_RDArrow,
         '//': Id.Expr_DSlash,