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Add support for Result types; Implement Try and either

This commit is contained in:
Zahary Karadjov 2020-04-08 16:24:48 +03:00
parent 8fd43269dc
commit 8e1755c4e1
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GPG Key ID: C8936F8A3073D609
4 changed files with 229 additions and 73 deletions
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213
stew/errorhandling.nim
View File

@ -1,9 +1,9 @@
import
typetraits, strutils,
typetraits, tables, strutils, options,
shims/macros, results
export
results
results, options
const
enforce_error_handling {.strdefine.}: string = "yes"
@ -158,55 +158,29 @@ template raising*[E, R](x: Raising[E, R]): R =
template raising*[R, E](x: Result[R, E]): R =
tryGet(x)
macro chk*(x: Result, handlers): untyped =
discard
const
incorrectChkSyntaxMsg =
"The `check` handlers block should consist of `ExceptionType: Value/Block` pairs"
macro chk*(x: Raising, handlers: untyped): untyped =
## The `chk` macro can be used in 2 different ways
##
## 1) Try to get the result of an expression. In case of any
## errors, substitute the result with a default value:
##
## ```
## let x = chk(foo(), defaultValue)
## ```
##
## We'll handle this case with a simple rewrite to
##
## ```
## let x = try: distinctBase(foo())
## except CatchableError: defaultValue
## ```
##
## 2) Try to get the result of an expression while providing exception
## handlers that must cover all possible recoverable errors.
##
## ```
## let x = chk foo():
## KeyError as err: defaultValue
## ValueError: return
## _: raise
## ```
##
## The above example will be rewritten to:
##
## ```
## let x = try:
## foo()
## except KeyError as err:
## defaultValue
## except ValueError:
## return
## except CatchableError:
## raise
## ```
##
## Please note that the special case `_` is considered equivalent to
## `CatchableError`.
##
## If the `chk` block lacks a default handler and there are unlisted
## recoverable errors, the compiler will fail to compile the code with
## a message indicating the missing ones.
template either*[E, R](x: Raising[E, R], otherwise: R): R =
try: distinctBase(x)
except CatchableError: otherwise
template either*[R, E](x: Result[R, E], otherwise: R): R =
let r = x
if isOk(r):
value(r)
else:
otherwise
template either*[T](x: Option[T], otherwise: T): T =
let o = x
if isSome(o):
get(o)
else:
otherwise
macro check*(x: Raising, handlers: untyped): untyped =
let
RaisingType = getTypeInst(x)
ErrorsSetTuple = RaisingType[1]
@ -230,13 +204,13 @@ macro chk*(x: Raising, handlers: untyped): untyped =
# Check how the API was used:
if handlers.kind != nnkStmtList:
# This is usage type 1: chk(foo(), defaultValue)
# This is usage type 1: check(foo(), defaultValue)
result.add newTree(nnkExceptBranch,
bindSym("CatchableError"),
newStmtList(handlers))
else:
var
# This will be a tuple of all the errors handled by the `chk` block.
# This will be a tuple of all the errors handled by the `check` block.
# In the end, we'll compare it to the Raising list.
HandledErrorsTuple = newNimNode(nnkPar, x)
# Has the user provided a default `_: value` handler?
@ -244,8 +218,7 @@ macro chk*(x: Raising, handlers: untyped): untyped =
for handler in handlers:
template err(msg: string) = error msg, handler
template unexpectedSyntax = err(
"The `chk` handlers block should consist of `ExceptionType: Value/Block` pairs")
template unexpectedSyntax = err incorrectChkSyntaxMsg
case handler.kind
of nnkCommentStmt:
@ -263,7 +236,7 @@ macro chk*(x: Raising, handlers: untyped): untyped =
result.add newTree(nnkExceptBranch, infix(ExceptionType, "as", exceptionVar),
valueBlock)
else:
err "The '$1' operator is not expected in a `chk` block" % [$handler[0]]
err "The '$1' operator is not expected in a `check` block" % [$handler[0]]
of nnkCall:
if handler.len != 2:
unexpectedSyntax
@ -284,3 +257,133 @@ macro chk*(x: Raising, handlers: untyped): untyped =
result)
storeMacroResult result
macro check*[R, E](x: Result[R, E], handlers: untyped): untyped =
if handlers.kind != nnkStmtList:
return newCall(bindSym"get", x, handlers)
let
R = getTypeInst(x)
SuccessResultType = R[1]
ErrorResultType = R[2]
let enumImpl = getImpl(ErrorResultType)[2]
if enumImpl.kind != nnkEnumTy:
error "`check` handler blocks can be used only with Results based on enums", x
let tempVar = genSym(nskLet, "res")
var errorsSwitch = newTree(nnkCaseStmt)
var defaultHandler: NimNode
errorsSwitch.add newCall(bindSym"error", tempVar)
for handler in handlers:
template err(msg: string) = error msg, handler
template unexpectedSyntax = err incorrectChkSyntaxMsg
case handler.kind
of nnkCommentStmt:
continue
of nnkInfix:
if eqIdent(handler[0], "as"):
if handler.len != 4:
err "The expected syntax is `ExceptionType as exceptionVar: Value/Block`"
let
ErrorType = handler[1]
valueBlock = handler[3]
errorsSwitch.add newTree(nnkOfBranch, ErrorType, valueBlock)
else:
err "The '$1' operator is not expected in a `check` block" % [$handler[0]]
of nnkCall:
if handler.len != 2:
unexpectedSyntax
let
ErrorType = handler[0]
valueBlock = handler[1]
if eqIdent(ErrorType, "_"):
if defaultHandler != nil:
err "Only a single default handler is expected"
defaultHandler = valueBlock
else:
errorsSwitch.add newTree(nnkOfBranch, ErrorType, valueBlock)
else:
unexpectedSyntax
if defaultHandler != nil:
errorsSwitch.add newTree(nnkElse, defaultHandler)
result = quote do:
let `tempVar` = `x`
if isOk `tempVar`:
get `tempVar`
else:
`errorsSwitch`
storeMacroResult result
macro Try*(body: typed, handlers: varargs[untyped]): untyped =
type ParamRegistryEntry = object
origSymbol: NimNode
newParam: NimNode
var params = initTable[string, ParamRegistryEntry]()
proc makeParam(replacedSym: NimNode,
registryEntry: var ParamRegistryEntry): NimNode =
if registryEntry.newParam == nil:
registryEntry.origSymbol = replacedSym
registryEntry.newParam = genSym(nskParam, $replacedSym)
return registryEntry.newParam
proc registerParamsInBody(n: NimNode) =
for i in 0 ..< n.len:
let son = n[i]
case son.kind
of nnkIdent, nnkCharLit..nnkTripleStrLit:
discard
of nnkSym:
if son.symKind in {nskLet, nskVar, nskForVar,
nskParam, nskTemp, nskResult}:
n[i] = makeParam(son, params.mgetOrPut(son.signatureHash,
default(ParamRegistryEntry)))
of nnkHiddenDeref:
registerParamsInBody son
n[i] = son[0]
else:
registerParamsInBody son
let procName = genSym(nskProc, "Try_payload")
var procBody = copy body
registerParamsInBody procBody
var raisesList = newTree(nnkBracket)
for handler in handlers:
raisesList.add handler[0]
var
procCall = newCall(procName)
procParams = @[newEmptyNode()]
for hash, param in params:
var paramType = getType(param.origSymbol)
if param.origSymbol.symKind in {nskVar, nskResult}:
if paramType.kind != nnkBracketExpr or not eqIdent(paramType[0], "var"):
paramType = newTree(nnkVarTy, paramType)
procParams.add newIdentDefs(param.newParam, paramType)
procCall.add param.origSymbol
let procPragma = newTree(nnkPragma,
newColonExpr(ident "raises", raisesList))
let generatedProc = newProc(name = procName,
params = procParams,
pragmas = procPragma,
body = procBody)
result = newTree(nnkTryStmt, newStmtList(generatedProc, procCall))
for handler in handlers: result.add handler
storeMacroResult result

2
stew/results.nim
View File

@ -257,7 +257,7 @@ type
Opt*[T] = Result[T, void]
func raiseResultError[T, E](self: Result[T, E]) {.noreturn, noinline.} =
func raiseResultError*[T, E](self: Result[T, E]) {.noreturn, noinline.} =
# noinline because raising should take as little space as possible at call
# site
mixin toException

50
tests/test_errorhandling.nim
View File

@ -7,7 +7,7 @@ proc bar(x: int): int {.noerrors.} =
proc toString(x: int): string {.errors: (ValueError, KeyError, OSError).} =
$x
enum
type
ReadStatus = enum
FileNotFound
AccessDenied
@ -19,28 +19,54 @@ proc readFromDevice(path: string): Result[seq[byte], ReadStatus] =
proc getGpsCoordinates(): Result[(float, float), cstring] =
ok (1.2, 3.4)
proc takeString(x: string) =
echo x
proc main =
let
a = bar(10)
b = raising toString(20)
c = chk toString(30):
ValueError: "got ValueError"
KeyError as err: err.msg
OSError: raise
c = check toString(30):
ValueError: "got ValueError"
KeyError as err: err.msg
OSError: raise
d = chk(readFromDevice("test"), @[1.byte, 2, 3])
e = chk readFromDevice("test"):
FileNotFound: raise newException()
HardwareError: quit 1
else: @[]
d = either(readFromDevice("test"), @[1.byte, 2, 3])
e = check readFromDevice("test"):
FileNotFound: raise newException(ValueError, "x")
HardwareError: quit 1
_: @[]
echo a
echo b
echo c
main()
let n = 10
var m = 23
proc main2(a: int, b: var int) =
var x = 10
var y = 20
var z = 23
Try:
echo a, b, x, y, z, n, m
if a > 20:
# raise newException(OSError, "Test")
discard
except ValueError:
discard
except IOError:
discard
var
p = 1
k = 2
main2 p, k
dumpMacroResults()
when false:
@ -51,6 +77,6 @@ when false:
proc map[A, E, R](a: A, f: proc (a: A): Raising[E, R])): string {.
errors: E|ValueError|ExtraErrors
.} =
$chk(f(a))
$check(f(a))
]#

37
tests/test_errorhandling.nim.generated.nim
View File

@ -1,17 +1,44 @@
## /home/zahary/nimbus/vendor/nim-stew/tests/test_errorhandling.nim(7, 32)
proc toString_15835040(x: int): string {.raises: [Defect, KeyError, OSError].} =
proc toString_16040040(x: int): string {.raises: [Defect, KeyError, OSError].} =
result = $x
template toString(x: int): untyped =
Raising[(ValueError, KeyError, OSError), string](toString_15835040(x))
Raising[(ValueError, KeyError, OSError), string](toString_16040040(x))
## /home/zahary/nimbus/vendor/nim-stew/tests/test_errorhandling.nim(14, 12)
## /home/zahary/nimbus/vendor/nim-stew/tests/test_errorhandling.nim(29, 14)
try:
[type node](Raising[(ValueError, KeyError, OSError), string](toString_15835040(30)))
[type node](Raising[(ValueError, KeyError, OSError), string](toString_16040040(30)))
except ValueError:
"got ValueError"
except KeyError as err:
err.msg
except OSError:
raise
raise
## /home/zahary/nimbus/vendor/nim-stew/tests/test_errorhandling.nim(36, 14)
let res_16125314 = readFromDevice("test")
if res_16125314.o: get res_16125314
else:
case error(res_16125314)
of FileNotFound:
raise
(ref ValueError)(msg: "x", parent: nil)
of HardwareError:
quit 1
else:
@[]
## /home/zahary/nimbus/vendor/nim-stew/tests/test_errorhandling.nim(54, 2)
try:
proc Try_payload_16170094(z_16170100: var int; y_16170099: var int; m_16170102: var int;
a_16170096: int; x_16170098: var int; b_16170097: var[int];
n_16170101: int) {.raises: [ValueError, IOError].} =
echo [a_16170096, b_16170097, x_16170098, y_16170099, z_16170100, n_16170101, m_16170102]
if (
20 < a_16170096):
discard
Try_payload_16170094(z, y, m, a, x, b, n)
except ValueError:
discard
except IOError:
discard