To start with a practical example, I would like to talk about, how I would
pattern match the NimNode types, mostly because they are types I would care
about. The syntax should be almost identical to the construction, just it
should work in reverse. Here is an example of how I could imagine it:
import macros
proc foobar(arg: NimNode, id: int): void =
echo arg.repr
macro myMacro(arg:untyped): untyped =
for section in arg:
case section # pattern matching is always the whole object, not just
the kind
of nnkCall.newTree(ident"variantA", `stmtList`):
foobar(stmtList, 0)
of nnkCall.newTree(ident"variontB", `stmtList`):
foobar(stmtList, 1)
of nnkCall.newTree(ident"variantC",
nnkStmtList.newTree(nnkCall.newTree(ident"subVariantA", `stmtList`))):
foobar(stmtList, 2)
of nnkCall.newTree(ident"variantC",
nnkStmtList.newTree(nnkCall.newTree(ident"subVariantB", `stmtList`))):
foobar(stmtList, 3)
Mymacro:
variantA:
a += 1
b += 2
variantB:
a += 4
b += 8
variantC:
subVariantA:
a += 8
b += 19
variantC:
subVariantB:
a += 20
b += 30
Full input ast:
StmtList
Call
Ident !"variantA"
StmtList
Infix
Ident !"+="
Ident !"a"
IntLit 1
Infix
Ident !"+="
Ident !"b"
IntLit 2
Call
Ident !"variantB"
StmtList
Infix
Ident !"+="
Ident !"a"
IntLit 4
Infix
Ident !"+="
Ident !"b"
IntLit 8
Call
Ident !"variantC"
StmtList
Call
Ident !"subVariantA"
StmtList
Infix
Ident !"+="
Ident !"a"
IntLit 8
Infix
Ident !"+="
Ident !"b"
IntLit 19
Call
Ident !"variantC"
StmtList
Call
Ident !"subVariantB"
StmtList
Infix
Ident !"+="
Ident !"a"
IntLit 20
Infix
Ident !"+="
Ident !"b"
IntLit 30
I have to admit thet `newTree` is not the best name to extract trees, but that
is the way I construct them, and that is the only syntax that works reliably
with every node kind.
