Add errorOption example to Readme

Added example for errorOption conversion in Readme.

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        nim: [stable, 1.4.8, 1.2.18]
+        nim: [stable, 1.6.16, 1.4.8, 1.2.18]
     steps:
     - uses: actions/checkout@v2
     - uses: iffy/install-nim@v3

Readme.md

@@ -12,14 +12,14 @@ Use the [Nimble][3] package manager to add `questionable` to an existing
 project. Add the following to its .nimble file:
 
 ```nim
-requires "questionable >= 0.10.5 & < 0.11.0"
+requires "questionable >= 0.10.15 & < 0.11.0"
 ```
 
 If you want to make use of Result types, then you also have to add either the
 [result][2] package, or the [stew][4] package:
 
 ```nim
-requires "result" # either this
+requires "results" # either this
 requires "stew"   # or this
 ```
 
@@ -151,7 +151,7 @@ have to explicitly import the `questionable/results` module:
 import questionable/results
 ```
 
-You can use `?!` make a Result type. These Result types either hold a value or
+You can use `?!` to make a Result type. These Result types either hold a value or
 an error. For example the type `?!int` is short for `Result[int, ref
 CatchableError]`.
 
@@ -226,6 +226,7 @@ Any Result can be converted to an Option:
 
 ```nim
 let converted = works().option  # equals @[1, 1, 2, 2, 2].some
+let errOption = fails().errorOption # option that is set when the Result holds an error
 ```
 
 [1]: https://nim-lang.org/docs/options.html

config.nims

@@ -1,5 +1,6 @@
 # Style Check
---styleCheck:usages
+if (NimMajor, NimMinor, NimPatch) >= (1, 6, 6):
+  --styleCheck:usages
 if (NimMajor, NimMinor) < (1, 6):
   --styleCheck:hint
 else:

questionable.nimble

@@ -1,10 +1,10 @@
-version = "0.10.5"
+version = "0.10.15"
 author = "Questionable Authors"
 description = "Elegant optional types"
 license = "MIT"
 
 task test, "Runs the test suite":
-  for module in ["options", "result", "stew"]:
+  for module in ["options", "results", "stew"]:
     withDir "testmodules/" & module:
       delEnv "NIMBLE_DIR" # use nimbledeps dir
       exec "nimble install -d -y"

questionable/binding.nim

@@ -2,15 +2,25 @@ import std/options
 import std/macros
 import ./private/binderror
 
-proc option[T](option: Option[T]): Option[T] =
+when (NimMajor, NimMinor) < (1, 1):
+  type SomePointer = ref | ptr | pointer
+elif (NimMajor, NimMinor) == (2, 0): # Broken in 2.0.0, fixed in 2.1.1.
+  type SomePointer = ref | ptr | pointer | proc
+else:
+  type SomePointer = ref | ptr | pointer | proc | iterator {.closure.}
+
+template toOption[T](option: Option[T]): Option[T] =
   option
 
+template toOption[T: SomePointer](value: T): Option[T] =
+  value.option
+
 proc placeholder(T: type): T =
   discard
 
-template bindLet(name, expression): bool =
+template bindLet(name, expression): untyped =
   let evaluated = expression
-  let option = evaluated.option
+  let option = evaluated.toOption
   type T = typeof(option.unsafeGet())
   let name {.used.} = if option.isSome:
     option.unsafeGet()
@@ -19,9 +29,9 @@ template bindLet(name, expression): bool =
     placeholder(T)
   option.isSome
 
-template bindVar(name, expression): bool =
+template bindVar(name, expression): untyped =
   let evaluated = expression
-  let option = evaluated.option
+  let option = evaluated.toOption
   type T = typeof(option.unsafeGet())
   var name {.used.} = if option.isSome:
     option.unsafeGet()
@@ -30,14 +40,50 @@ template bindVar(name, expression): bool =
     placeholder(T)
   option.isSome
 
+proc newUnpackTupleNode(names: NimNode, value: NimNode): NimNode =
+  # builds tuple unpacking statement, eg: let (a, b) = value
+  let vartuple = nnkVarTuple.newTree()
+  for i in 0..<names.len:
+    vartuple.add names[i]
+  vartuple.add newEmptyNode()
+  vartuple.add value
+  nnkLetSection.newTree(vartuple)
+
+macro bindTuple(names, expression): bool =
+  let opt = genSym(nskLet, "option")
+  let evaluated = genSym(nskLet, "evaluated")
+  let T = genSym(nskType, "T")
+
+  let value = quote do:
+    if `opt`.isSome:
+      `opt`.unsafeGet()
+    else:
+      bindFailed(`evaluated`)
+      placeholder(`T`)
+
+  let letsection = newUnpackTupleNode(names, value)
+
+  quote do:
+    let `evaluated` = `expression`
+    let `opt` = `evaluated`.toOption
+    type `T` = typeof(`opt`.unsafeGet())
+    `letsection`
+    `opt`.isSome
+
 macro `=?`*(name, expression): bool =
   ## The `=?` operator lets you bind the value inside an Option or Result to a
   ## new variable. It can be used inside of a conditional expression, for
   ## instance in an `if` statement.
 
-  name.expectKind({nnkIdent, nnkVarTy})
+  when (NimMajor, NimMinor) < (1, 6):
+    name.expectKind({nnkIdent, nnkVarTy, nnkTupleConstr, nnkPar})
+  else:
+    name.expectKind({nnkIdent, nnkVarTy, nnkTupleConstr})
+
   if name.kind == nnkIdent:
     quote do: bindLet(`name`, `expression`)
+  elif name.kind == nnkTupleConstr or name.kind == nnkPar:
+    quote do: bindTuple(`name`, `expression`)
   else:
     let name = name[0]
     quote do: bindVar(`name`, `expression`)

questionable/chaining.nim

@@ -15,50 +15,34 @@ macro expectReturnType(identifier: untyped, expression: untyped): untyped =
     when compiles(`expression`) and not compiles(typeof `expression`):
       {.error: `message`.}
 
-template `.?`*(option: typed, identifier: untyped{nkIdent}): untyped =
-  ## The `.?` chaining operator is used to safely access fields and call procs
-  ## on Options or Results. The expression is only evaluated when the preceding
-  ## Option or Result has a value.
-
+template chain(option: typed, identifier: untyped{nkIdent}): untyped =
   # chain is of shape: option.?identifier
   expectReturnType(identifier, option.unsafeGet.identifier)
   option ->? option.unsafeGet.identifier
 
-macro `.?`*(option: typed, infix: untyped{nkInfix}): untyped =
-  ## The `.?` chaining operator is used to safely access fields and call procs
-  ## on Options or Results. The expression is only evaluated when the preceding
-  ## Option or Result has a value.
-
+macro chain(option: typed, infix: untyped{nkInfix}): untyped =
   # chain is of shape: option.?left `operator` right
+  let infix = infix.copyNimTree()
   let left = infix[1]
   infix[1] = quote do: `option`.?`left`
   infix
 
-macro `.?`*(option: typed, bracket: untyped{nkBracketExpr}): untyped =
-  ## The `.?` chaining operator is used to safely access fields and call procs
-  ## on Options or Results. The expression is only evaluated when the preceding
-  ## Option or Result has a value.
-
+macro chain(option: typed, bracket: untyped{nkBracketExpr}): untyped =
   # chain is of shape: option.?left[right]
+  let bracket = bracket.copyNimTree()
   let left = bracket[0]
   bracket[0] = quote do: `option`.?`left`
   bracket
 
-macro `.?`*(option: typed, dot: untyped{nkDotExpr}): untyped =
-  ## The `.?` chaining operator is used to safely access fields and call procs
-  ## on Options or Results. The expression is only evaluated when the preceding
-  ## Option or Result has a value.
-
+macro chain(option: typed, dot: untyped{nkDotExpr}): untyped =
   # chain is of shape: option.?left.right
+  let dot = dot.copyNimTree()
   let left = dot[0]
   dot[0] = quote do: `option`.?`left`
   dot
 
-macro `.?`*(option: typed, call: untyped{nkCall}): untyped =
-  ## The `.?` chaining operator is used to safely access fields and call procs
-  ## on Options or Results. The expression is only evaluated when the preceding
-  ## Option or Result has a value.
-
+macro chain(option: typed, call: untyped{nkCall}): untyped =
+  let call = call.copyNimTree()
   let procedure = call[0]
   if call.len == 1:
     # chain is of shape: option.?procedure()
@@ -81,11 +65,15 @@ macro `.?`*(option: typed, call: untyped{nkCall}): untyped =
       expectReturnType(`procedure`, `call`)
       `option` ->? `call`
 
-macro `.?`*(option: typed, symbol: untyped): untyped =
-  ## The `.?` chaining operator is used to safely access fields and call procs
-  ## on Options or Results. The expression is only evaluated when the preceding
-  ## Option or Result has a value.
-
+macro chain(option: typed, symbol: untyped): untyped =
   symbol.expectSym()
   let expression = ident($symbol)
   quote do: `option`.?`expression`
+
+template `.?`*(left: typed, right: untyped): untyped =
+  ## The `.?` chaining operator is used to safely access fields and call procs
+  ## on Options or Results. The expression is only evaluated when the preceding
+  ## Option or Result has a value.
+  block:
+    let evaluated = left
+    chain(evaluated, right)

questionable/indexing.nim

@@ -1,11 +1,32 @@
 import std/macros
+import std/options
+
+proc safeGet[T](expression: seq[T] | openArray[T], index: int): Option[T] =
+  if index >= expression.low and index <= expression.high:
+    expression[index].some
+  else:
+    T.none
+
+proc safeGet(expression: string, index: int): Option[char] =
+  if index >= expression.low and index <= expression.high:
+    expression[index].some
+  else:
+    char.none
+
+macro `.?`*(expression: seq | string | openArray, brackets: untyped{nkBracket}): untyped =
+    # chain is of shape: (seq or string or openArray).?[index]
+    let index = brackets[0]
+    quote do:
+      block:
+        safeGet(`expression`, `index`)
 
 macro `.?`*(expression: typed, brackets: untyped{nkBracket}): untyped =
   # chain is of shape: expression.?[index]
   let index = brackets[0]
   quote do:
-    type T = typeof(`expression`[`index`])
-    try:
-      `expression`[`index`].some
-    except KeyError:
-      T.none
+    block:
+      type T = typeof(`expression`[`index`])
+      try:
+        `expression`[`index`].some
+      except KeyError:
+        T.none

questionable/operators.nim

@@ -1,12 +1,19 @@
 template liftUnary*(T: type, operator: untyped) =
 
   template `operator`*(a: T): untyped =
-    a ->? `operator`(a.unsafeGet())
+    block:
+      let evaluated = a
+      evaluated ->? `operator`(evaluated.unsafeGet())
 
 template liftBinary*(T: type, operator: untyped) =
 
   template `operator`*(a: T, b: T): untyped =
-    (a, b) ->? `operator`(a.unsafeGet, b.unsafeGet)
+    block:
+      let evalA = a
+      let evalB = b
+      (evalA, evalB) ->? `operator`(evalA.unsafeGet, evalB.unsafeGet)
 
   template `operator`*(a: T, b: typed): untyped =
-    a ->? `operator`(a.unsafeGet(), b)
+    block:
+      let evalA = a
+      evalA ->? `operator`(evalA.unsafeGet(), b)

questionable/options.nim

@@ -44,7 +44,7 @@ template `->?`*[T,U,V](options: (?T, ?U), expression: ?V): ?V =
 template `->?`*[T,U,V](options: (?T, ?U), expression: V): ?V =
   options ->? expression.some
 
-template `|?`*[T](option: ?T, fallback: T): T =
+proc `|?`*[T](option: ?T, fallback: T): T =
   ## Use the `|?` operator to supply a fallback value when an Option does not
   ## hold a value.
 
@@ -56,11 +56,13 @@ template `|?`*[T](option: ?T, fallback: T): T =
 macro `.?`*[T](option: ?T, brackets: untyped{nkBracket}): untyped =
   let index = brackets[0]
   quote do:
-    type U = typeof(`option`.unsafeGet().?[`index`].unsafeGet())
-    if `option`.isSome:
-      `option`.unsafeGet().?[`index`]
-    else:
-      U.none
+    block:
+      let evaluated = `option`
+      type U = typeof(evaluated.unsafeGet().?[`index`].unsafeGet())
+      if evaluated.isSome:
+        evaluated.unsafeGet().?[`index`]
+      else:
+        U.none
 
 Option.liftUnary(`-`)
 Option.liftUnary(`+`)

questionable/private/bareexcept.nim

@@ -0,0 +1,6 @@
+template ignoreBareExceptWarning*(body) =
+  when defined(nimHasWarnBareExcept):
+    {.push warning[BareExcept]:off warning[UnreachableCode]:off.}
+  body
+  when defined(nimHasWarnBareExcept):
+    {.pop.}

questionable/private/binderror.nim

@@ -1,24 +1,54 @@
 import std/options
+import std/macros
 
-var captures {.global, compileTime.}: int
-var errorVariable: ptr ref CatchableError
+# A stack of names of error variables. Keeps track of the error variables that
+# are given to captureBindError().
+var errorVariableNames {.global, compileTime.}: seq[string]
 
-template captureBindError*(error: var ref CatchableError, expression): auto =
-  let previousErrorVariable = errorVariable
-  errorVariable = addr error
+macro captureBindError*(error: var ref CatchableError, expression): auto =
+  ## Ensures that an error is assigned to the error variable when a binding (=?)
+  ## fails inside the expression.
 
-  static: inc captures
-  let evaluated = expression
-  static: dec captures
+  # name of the error variable as a string literal
+  let errorVariableName = newLit($error)
 
-  errorVariable = previousErrorVariable
+  let evaluated = genSym(nskLet, "evaluated")
+  quote do:
+    # add error variable to the top of the stack
+    static: errorVariableNames.add(`errorVariableName`)
+    # evaluate the expression
+    let `evaluated` = `expression`
+    # pop error variable from the stack
+    static: discard errorVariableNames.pop()
+    # return the evaluated result
+    `evaluated`
 
-  evaluated
-
-func error[T](option: Option[T]): ref CatchableError =
+func unsafeCatchableError[T](_: Option[T]): ref CatchableError =
   newException(ValueError, "Option is set to `none`")
 
-template bindFailed*(expression) =
-  when captures > 0:
-    mixin error
-    errorVariable[] = expression.error
+func unsafeCatchableError[T](_: ref T): ref CatchableError =
+  newException(ValueError, "ref is nil")
+
+func unsafeCatchableError[T](_: ptr T): ref CatchableError =
+  newException(ValueError, "ptr is nil")
+
+func unsafeCatchableError[Proc: proc | iterator](_: Proc): ref CatchableError =
+  newException(ValueError, "proc or iterator is nil")
+
+macro bindFailed*(expression: typed) =
+  ## Called when a binding (=?) fails.
+  ## Assigns an error to the error variable (specified in captureBindError())
+  ## when appropriate.
+
+  # The `expression` parameter is typed to ensure that the compiler does not
+  # expand bindFailed() before it expands invocations of captureBindError().
+
+  # check that we have an error variable on the stack
+  if errorVariableNames.len > 0:
+    # create an identifier that references the current error variable
+    let errorVariable = ident errorVariableNames[^1]
+    return quote do:
+      # check that the error variable is in scope
+      when compiles(`errorVariable`):
+        # assign bind error to error variable
+        `errorVariable` = `expression`.unsafeCatchableError

questionable/results.nim

@@ -7,6 +7,7 @@ import ./indexing
 import ./operators
 import ./without
 import ./withoutresult
+import ./private/bareexcept
 
 include ./private/errorban
 
@@ -73,6 +74,12 @@ proc isFailure*[T](value: ?!T): bool =
 
   value.isErr
 
+proc `$`*[T](value: ?!T): string =
+  if value.isSuccess:
+    "success(" & $(!value) & ")"
+  else:
+    "failure(\"" & $(value.error.msg) & "\")"
+
 template `->?`*[T,U](value: ?!T, expression: ?!U): ?!U =
   if value.isFailure:
     U.failure(value.error)
@@ -93,7 +100,7 @@ template `->?`*[T,U,V](values: (?!T, ?!U), expression: ?!V): ?!V =
 template `->?`*[T,U,V](values: (?!T, ?!U), expression: V): ?!V =
   values ->? expression.success
 
-template `|?`*[T,E](value: Result[T,E], fallback: T): T =
+proc `|?`*[T,E](value: Result[T,E], fallback: T): T =
   ## Use the `|?` operator to supply a fallback value when a Result does not
   ## hold a value.
 
@@ -103,12 +110,30 @@ proc option*[T,E](value: Result[T,E]): ?T =
   ## Converts a Result into an Option.
 
   if value.isOk:
-    try: # workaround for erroneous exception tracking when T is a closure
-      value.unsafeGet.some
-    except Exception as exception:
-      raise newException(Defect, exception.msg, exception)
+    ignoreBareExceptWarning:
+      try: # workaround for erroneous exception tracking when T is a closure
+        return value.unsafeGet.some
+      except Exception as exception:
+        raise newException(Defect, exception.msg, exception)
   else:
-    T.none
+    return T.none
+
+template toOption*[T, E](value: Result[T, E]): ?T =
+  ## Converts a Result into an Option.
+
+  value.option
+
+proc unsafeCatchableError*[T, E](value: Result[T, E]): ref CatchableError =
+  ## Returns the error from the Result, converted to `ref CatchableError` if
+  ## necessary. Behaviour is undefined when the result holds a value instead of
+  ## an error.
+  when E is ref CatchableError:
+    value.unsafeError
+  else:
+    when compiles($value.unsafeError):
+      newException(ResultFailure, $value.unsafeError)
+    else:
+      newException(ResultFailure, "Result is an error")
 
 proc errorOption*[T, E](value: Result[T, E]): ?E =
   ## Returns an Option that contains the error from the Result, if it has one.

questionable/resultsbase.nim

@@ -1,7 +1,7 @@
 template tryImport(module) = import module
 
-when compiles tryImport pkg/result:
-  import pkg/result/../results
+when compiles tryImport pkg/results:
+  import pkg/results
 else:
   import pkg/stew/results
 

questionable/withoutresult.nim

@@ -2,16 +2,18 @@ import std/macros
 import ./without
 import ./private/binderror
 
+const symbolKinds = {nnkSym, nnkOpenSymChoice, nnkClosedSymChoice}
+const identKinds = {nnkIdent} + symbolKinds
+
 proc undoSymbolResolution(expression, ident: NimNode): NimNode =
   ## Finds symbols in the expression that match the `ident` and replaces them
   ## with `ident`, effectively undoing any symbol resolution that happened
   ## before.
 
-  const symbolKinds = {nnkSym, nnkOpenSymChoice, nnkClosedSymChoice}
-
   if expression.kind in symbolKinds and eqIdent($expression, $ident):
     return ident
 
+  let expression = expression.copyNimTree()
   for i in 0..<expression.len:
     expression[i] = undoSymbolResolution(expression[i], ident)
 
@@ -21,6 +23,9 @@ macro without*(condition, errorname, body: untyped): untyped =
   ## Used to place guards that ensure that a Result contains a value.
   ## Exposes error when Result does not contain a value.
 
+  if errorname.kind notin identKinds:
+    error("expected an identifier, got " & errorname.repr, errorname)
+
   let errorIdent = ident $errorname
 
   # Nim's early symbol resolution might have picked up a symbol with the
@@ -29,7 +34,7 @@ macro without*(condition, errorname, body: untyped): untyped =
   let body = body.undoSymbolResolution(errorIdent)
 
   quote do:
-    var error: ref CatchableError
+    var error {.gensym.}: ref CatchableError
 
     without captureBindError(error, `condition`):
       template `errorIdent`: ref CatchableError = error

testmodules/options/config.nims

@@ -0,0 +1,2 @@
+--path:"../.."
+import "../../config.nims"

testmodules/options/nim.cfg

@@ -1 +0,0 @@
---path:"../.."

testmodules/options/test.nim

@@ -115,17 +115,6 @@ suite "optionals":
     else:
       fail
 
-  test "=? evaluates optional expression only once":
-    var count = 0
-    if a =? (inc count; 42.some):
-      let b {.used.} = a
-    check count == 1
-
-    count = 0
-    if var a =? (inc count; 42.some):
-      let b {.used.} = a
-    check count == 1
-
   test "=? works in generic code":
     proc toString[T](option: ?T): string =
       if value =? option:
@@ -176,6 +165,150 @@ suite "optionals":
     else:
       fail()
 
+  test "=? works with reference types":
+    var x = new int
+    x[] = 42
+    if a =? x:
+      check a[] == 42
+    else:
+      fail
+
+    x = nil
+    if a =? x:
+      fail
+
+    var p = proc = discard
+    if a =? p:
+      a()
+    else:
+      fail
+
+    p = nil
+    if a =? p:
+      fail
+
+    when (NimMajor, NimMinor) >= (1, 1) and (NimMajor, NimMinor) != (2, 0):
+      var it = iterator: int = yield 2
+      if a =? it:
+        for x in a:
+          check x == 2
+      else:
+        fail
+
+      it = nil
+      if a =? it:
+        fail
+
+  test "=? rejects non-reference types":
+    check `not` compiles do:
+      if a =? 0:
+        discard
+    check `not` compiles do:
+      if var a =? 0:
+        discard
+    check `not` compiles do:
+      if (a,) =? (0,):
+        discard
+
+  test "=? works with custom optional types":
+    type MyOption = distinct int
+    proc isSome(x: MyOption): bool = x.int >= 0
+    proc unsafeGet(x: MyOption): int = x.int
+    template toOption(x: MyOption): MyOption = x
+
+    if a =? MyOption 42:
+      check a == 42
+    else:
+      fail
+
+    if a =? MyOption -1:
+      fail
+
+  test "=? binds and unpacks tuples":
+    if (a, b) =? (some ("test", 1)):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+    if (a, b) =? none (string, int):
+      discard a
+      discard b
+      fail()
+
+  test "=? binds and unpacks tuples with named fields":
+    if (a, b) =? (some (desc: "test", id: 1)):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples returned from proc":
+    proc returnsTuple(): ?tuple[name: string, id: int] = some ("test", 1)
+
+    if (a, b) =? returnsTuple():
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples returned from proc with unnamed fields":
+    proc returnsTuple(): ?(string, int,) = some ("test", 1,)
+
+    if (a, b,) =? returnsTuple():
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples with _":
+    if (_, b) =? some ("test", 1):
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples with named fields":
+    if (a, b) =? some (desc: "test", id: 1):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds variable to tuples with named fields":
+    if t =? some (desc: "test", id: 1):
+      check t.desc == "test"
+      check t.id == 1
+    else:
+      fail()
+
+  test "=? binds to tuple types":
+    type MyTuple = tuple
+      desc: string
+      id: int
+
+    let mt: MyTuple = ("test", 1)
+
+    if t =? (some mt):
+      check t.desc == "test"
+      check t.id == 1
+    else:
+      fail()
+
+    if (a, b) =? (some mt):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? for tuples does not leak symbols into caller's scope":
+    const evaluated = ""
+    type T = string
+    if (a,) =? some (0,):
+      check a == 0
+      check option is proc
+      check evaluated is string
+      check T is string
+
   test "without statement can be used for early returns":
     proc test1 =
       without a =? 42.some:
@@ -202,6 +335,31 @@ suite "optionals":
     check table.?["a"] == 1.some
     check table.?["c"] == int.none
 
+  test ".?[] can be used for indexing strings without raising IndexDefect":
+    let str = "a"
+    check str.?[0] == 'a'.some
+    check str.?[1] == char.none
+    check str.?[-1] == char.none
+
+  test ".?[] can be used for indexing sequences without raising IndexDefect":
+    let sequence = @[1]
+    check sequence.?[0] == 1.some
+    check sequence.?[1] == int.none
+    check sequence.?[-1] == int.none
+
+  test ".?[] can be used for indexing openArrays without raising IndexDefect":
+    proc checkOpenArray(oa: openArray[int]): void =
+      check oa.?[0] == 1.some
+      check oa.?[1] == int.none
+      check oa.?[-1] == int.none
+
+    checkOpenArray(@[1])
+
+  test ".?[] evaluates openArray expression only once":
+    var count = 0
+    discard (inc count; @[1].toOpenArray(0, 0)).?[0]
+    check count == 1
+
   test ".?[] can be followed by calls, operators and indexing":
     let table = @{"a": @[41, 42]}.toTable
     check table.?["a"].isSome
@@ -274,6 +432,58 @@ suite "optionals":
 
     check a.?[1] == 42.some
 
+  test ".? chain evaluates optional expression only once":
+    var count = 0
+    discard (inc count; @[41, 42].some).?len
+    check count == 1
+
+  test "=? evaluates optional expression only once":
+    var count = 0
+    if a =? (inc count; 42.some):
+      let b {.used.} = a
+    check count == 1
+
+    count = 0
+    if var a =? (inc count; 42.some):
+      let b {.used.} = a
+    check count == 1
+
+  test "|? evaluates optional expression only once":
+    var count = 0
+    discard (inc count; 42.some) |? 43
+    check count == 1
+
+  test ".?[] evaluates optional expression only once":
+    # indexing on optional sequence:
+    block:
+      var count = 0
+      discard (inc count; @[41, 42].some).?[0]
+      check count == 1
+    # indexing on normal sequence:
+    block:
+      var count = 0
+      discard (inc count; @[41, 42]).?[0]
+      check count == 1
+
+  test "lifted unary operators evaluate optional expression only once":
+    var count = 0
+    discard -(inc count; 42.some)
+    check count == 1
+
+  test "lifted binary operators evaluate optional expressions only once":
+    # lifted operator on two options:
+    block:
+      var count1, count2 = 0
+      discard (inc count1; 40.some) + (inc count2; 2.some)
+      check count1 == 1
+      check count2 == 1
+    # lifted operator on option and value:
+    block:
+      var count1, count2 = 0
+      discard (inc count1; 40.some) + (inc count2; 2)
+      check count1 == 1
+      check count2 == 1
+
   test "examples from readme work":
 
     var x: ?int

testmodules/options/test.nimble

@@ -4,7 +4,7 @@ description = "Questionable tests for std/option"
 license = "MIT"
 
 task test, "Runs the test suite":
-  var options = "-f -r"
+  var options = "-f -r --skipParentCfg"
   when (NimMajor, NimMinor) >= (1, 4):
     options &= " --warningAsError[UnsafeDefault]:on"
     options &= " --warningAsError[ProveInit]:on"

testmodules/result/nim.cfg

@@ -1 +0,0 @@
---path:"../.."

testmodules/results/config.nims

@@ -0,0 +1,3 @@
+--path:"../.."
+--threads:on
+import "../../config.nims"

testmodules/results/test.nim

@@ -3,8 +3,11 @@ import std/options
 import std/sequtils
 import std/strutils
 import std/sugar
+import std/threadpool
 import pkg/questionable/results
 
+{.experimental: "parallel".}
+
 suite "result":
 
   let error = newException(CatchableError, "error")
@@ -14,6 +17,10 @@ suite "result":
     check (?!string is Result[string, ref CatchableError])
     check (?!seq[bool] is Result[seq[bool], ref CatchableError])
 
+  test "conversion to string $ works for ?!Types":
+    check $42.success == "success(42)"
+    check $(int.failure "some error") == "failure(\"some error\")"
+
   test "! gets value or raises Defect":
     check !42.success == 42
     expect Defect: discard !int.failure error
@@ -165,6 +172,82 @@ suite "result":
 
     check called
 
+  test "=? binds and unpacks tuples":
+    if (a, b) =? (success ("test", 1)):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+    if (a, b) =? (string, int).failure(error):
+      discard a
+      discard b
+      fail()
+
+  test "=? binds and unpacks tuples with named fields":
+    if (a, b) =? (success (desc: "test", id: 1)):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples returned from proc":
+    proc returnsTuple(): ?!tuple[name: string, id: int] = success ("test", 1)
+
+    if (a, b) =? returnsTuple():
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples returned from proc with unnamed fields":
+    proc returnsTuple(): ?!(string, int,) = success ("test", 1,)
+
+    if (a, b,) =? returnsTuple():
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples with _":
+    if (_, b) =? success ("test", 1):
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds and unpacks tuples with named fields":
+    if (a, b) =? success (desc: "test", id: 1):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
+  test "=? binds variable to tuples with named fields":
+    if t =? success (desc: "test", id: 1):
+      check t.desc == "test"
+      check t.id == 1
+    else:
+      fail()
+
+  test "=? binds to tuple types":
+    type MyTuple = tuple
+      desc: string
+      id: int
+
+    let mt: MyTuple = ("test", 1)
+
+    if t =? (success mt):
+      check t.desc == "test"
+      check t.id == 1
+    else:
+      fail()
+
+    if (a, b) =? (success mt):
+      check a == "test"
+      check b == 1
+    else:
+      fail()
+
   test "without statement works for results":
     proc test1 =
       without a =? 42.success:
@@ -243,6 +326,48 @@ suite "result":
     test1()
     test2()
 
+  test "without statement with error handles references as well":
+    proc test =
+      var x: ref int = nil
+      without a =? x, error:
+        check error.msg == "ref is nil"
+        return
+      fail
+
+    test()
+
+  test "without statement with error handles pointers as well":
+    proc test =
+      var x: ptr int = nil
+      without a =? x, error:
+        check error.msg == "ptr is nil"
+        return
+      fail
+
+    test()
+
+  test "without statement with error handles closures as well":
+    proc test =
+      var x = proc = discard
+      x = nil
+      without a =? x, error:
+        check error.msg == "proc or iterator is nil"
+        return
+      fail
+
+    test()
+
+  test "without statement with error handles iterators as well":
+    when (NimMajor, NimMinor) != (2, 0):
+      proc test =
+        var x: iterator: int = nil
+        without a =? x, error:
+          check error.msg == "proc or iterator is nil"
+          return
+        fail
+
+      test()
+
   test "without statement with error can be used more than once":
     proc test =
       without a =? 42.success, error:
@@ -321,6 +446,25 @@ suite "result":
 
     foo()
 
+  test "without statement with error works with multiple threads":
+    proc fail(number: int) =
+      without _ =? int.failure "error" & $number, error:
+        check error.msg == "error" & $number
+    parallel:
+      for i in 0..<1000:
+        spawn fail(i)
+
+  test "without statement doesn't interfere with generic code called elsewhere":
+    proc foo(_: type): ?!int =
+      if error =? success(1).errorOption:
+        discard
+
+    proc bar {.used.} = # defined, but not used
+      without x =? bool.foo(), error:
+        discard error
+
+    discard bool.foo() # same type parameter 'bool' as used in bar()
+
   test "catch can be used to convert exceptions to results":
     check parseInt("42").catch == 42.success
     check parseInt("foo").catch.error of ValueError
@@ -396,6 +540,61 @@ suite "result":
 
     check (a & b) == 42.success
 
+  test ".? chain evaluates result only once":
+    var count = 0
+    discard (inc count; @[41, 42].success).?len
+    check count == 1
+
+  test "=? evaluates result only once":
+    var count = 0
+    if a =? (inc count; 42.success):
+      let b {.used.} = a
+    check count == 1
+
+    count = 0
+    if var a =? (inc count; 42.success):
+      let b {.used.} = a
+    check count == 1
+
+  test "|? evaluates result only once":
+    var count = 0
+    discard (inc count; 42.success) |? 43
+    check count == 1
+
+  test ".?[] evaluates result only once":
+    var count = 0
+    discard (inc count; @[41, 42].success).?[0]
+    check count == 1
+
+  test "lifted unary operators evaluate result only once":
+    var count = 0
+    discard -(inc count; 42.success)
+    check count == 1
+
+  test "lifted binary operators evaluate results only once":
+    # lifted operator on two options:
+    block:
+      var count1, count2 = 0
+      discard (inc count1; 40.success) + (inc count2; 2.success)
+      check count1 == 1
+      check count2 == 1
+    # lifted operator on option and value:
+    block:
+      var count1, count2 = 0
+      discard (inc count1; 40.success) + (inc count2; 2)
+      check count1 == 1
+      check count2 == 1
+
+  test "conversion to option evaluates result only once":
+    var count = 0
+    discard (inc count; 42.success).option
+    check count == 1
+
+  test "conversion to error evaluates result only once":
+    var count = 0
+    discard (inc count; int.failure(error)).errorOption
+    check count == 1
+
   test "examples from readme work":
 
     proc works: ?!seq[int] =
@@ -444,6 +643,19 @@ suite "result":
     someProc(42.success)
     someProc(int.failure "some error")
 
+type TypeWithSideEffect = object
+proc `$`*(value: TypeWithSideEffect): string {.sideEffect.} =
+  discard
+
+suite "result side effects":
+
+  test "without statement with error works when `$` has side effects":
+    proc foo =
+      without x =? TypeWithSideEffect.failure("error"), error:
+        discard error
+        return
+      fail()
+    foo()
 
 import pkg/questionable/resultsbase
 
@@ -451,7 +663,7 @@ suite "result compatibility":
 
   type R = Result[int, string]
   let good = R.ok 42
-  let bad = R.err "error"
+  let bad = R.err "some error"
 
   test "|?, =? and .option work on other types of Result":
     check bad |? 43 == 43
@@ -469,3 +681,13 @@ suite "result compatibility":
       fail
     without b =? good:
       fail
+
+  test "without statement with error works on other type of Result":
+    without value =? bad, error:
+      check error of ResultFailure
+      check error.msg == "some error"
+
+  test "without statement with error works on Result[T, void]":
+    without value =? Result[int, void].err, error:
+      check error of ResultFailure
+      check error.msg == "Result is an error"

testmodules/results/test.nimble

@@ -3,7 +3,7 @@ author = "Questionable Authors"
 description = "Questionable tests for pkg/result"
 license = "MIT"
 
-requires "result"
+requires "results"
 
 task test, "Runs the test suite":
-  exec "nim c -f -r test.nim"
+  exec "nim c -f -r --skipParentCfg test.nim"

testmodules/stew/config.nims

@@ -0,0 +1,3 @@
+--path:"../.."
+--threads:on
+import "../../config.nims"

testmodules/stew/nim.cfg

@@ -1 +0,0 @@
---path:"../.."

testmodules/stew/test.nim

@@ -1 +1 @@
-include ../result/test
+include ../results/test

testmodules/stew/test.nimble

@@ -3,7 +3,11 @@ author = "Questionable Authors"
 description = "Questionable tests for pkg/stew"
 license = "MIT"
 
-requires "stew"
+when (NimMajor, NimMinor) >= (1, 6):
+  requires "stew"
 
-task test, "Runs the test suite":
-  exec "nim c -f -r test.nim"
+  task test, "Runs the test suite":
+    exec "nim c -f -r --skipParentCfg test.nim"
+else:
+  task test, "Runs the test suite":
+    echo "Warning: Skipping test with stew on Nim < 1.6"