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add enumerate macro (#15297)

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* add `enumerate` macro

* address the comments

* put `enumerate` in its own module
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Miran 2020-09-22 13:08:36 +02:00 • committed by GitHub
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3 changed files with 63 additions and 5 deletions
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doc/manual.rst
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@ -5508,10 +5508,11 @@ type ``system.ForLoopStmt`` can rewrite the entirety of a ``for`` loop:
macro enumerate(x: ForLoopStmt): untyped =
expectKind x, nnkForStmt
# we strip off the first for loop variable and use
# it as an integer counter:
# check if the starting count is specified:
var countStart = if x[^2].len == 2: newLit(0) else: x[^2][1]
result = newStmtList()
result.add newVarStmt(x[0], newLit(0))
# we strip off the first for loop variable and use it as an integer counter:
result.add newVarStmt(x[0], countStart)
var body = x[^1]
if body.kind != nnkStmtList:
body = newTree(nnkStmtList, body)
@ -5520,7 +5521,7 @@ type ``system.ForLoopStmt`` can rewrite the entirety of a ``for`` loop:
for i in 1..x.len-3:
newFor.add x[i]
# transform enumerate(X) to 'X'
newFor.add x[^2][1]
newFor.add x[^2][^1]
newFor.add body
result.add newFor
# now wrap the whole macro in a block to create a new scope
@ -5532,7 +5533,7 @@ type ``system.ForLoopStmt`` can rewrite the entirety of a ``for`` loop:
# without wrapping the macro in a block, we'd need to choose different
# names for `a` and `b` here to avoid redefinition errors
for a, b in enumerate([1, 2, 3, 5]):
for a, b in enumerate(10, [1, 2, 3, 5]):
echo a, " ", b