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sugar: add var x syntax to => #1492

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Feb 18, 2025
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sugar: add var x syntax to => #1492

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7 changes: 6 additions & 1 deletion lib/pure/sugar.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -53,7 +53,8 @@ proc createProcType(p, b: NimNode): NimNode =
result.add prag

macro `=>`*(p, b: untyped): untyped =
## Syntax sugar for anonymous procedures. It also supports pragmas.
## Syntax sugar for anonymous procedures. It also supports pragmas. Prefixing
## a parameter name with ``var`` makes the parameter a var parameter.
##
## .. warning:: Semicolons can not be used to separate procedure arguments.
runnableExamples:
Expand Down Expand Up @@ -109,6 +110,10 @@ macro `=>`*(p, b: untyped): untyped =
identDefs.add(newIdentNode("auto"))
identDefs.add(newEmptyNode())
inc untypedBeforeColon
of nnkVarTy:
identDefs.add(c[0])
identDefs.add(newTree(nnkVarTy, newIdentNode("auto")))
identDefs.add(newEmptyNode())
of nnkInfix:
if c[0].kind == nnkIdent and c[0].eqIdent"->":
var procTy = createProcType(c[1], c[2])
Expand Down
21 changes: 21 additions & 0 deletions tests/lang_callable/macros/tsugar_closuremacro.nim
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Expand Up @@ -78,3 +78,24 @@ type
var myBot = Bot()
myBot.call = () {.noSideEffect.} => "I'm a bot."
doAssert myBot.call() == "I'm a bot."

proc singleVar(p: (var int) -> int): int =
var x = 0
discard p(x)
x

doAssert singleVar((x: var auto) => (inc x; x)) == 1

proc trailingVar(p: (int, var int) -> int): int =
var x = 0
discard p(1, x)
x

doAssert trailingVar((x, var y) => (y += x; 0)) == 1

proc multiVar(p: (int, var int, var int) -> int): int =
var x, y = 0
discard p(1, x, y)
x

doAssert multiVar((x, var y, var z) => x) == 0
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