I just want to make fun with Julia macro ... '@awhen' will set the first `expr` as `it` in a let block. and then use `it` in remain arguments. eg: `@awhen([1,2,3,4], it[1], it[2])`
Johan Sigfrids於 2015年3月16日星期一 UTC+8下午5時34分18秒寫道： > > What is that macro supposed to do? > > On Monday, March 16, 2015 at 7:12:14 AM UTC+2, Miao Yang wrote: >> >> macro awhen(expr, body...) >> esc(quote >> let it = $(expr) >> if it != nothing >> $(body...) >> end >> end >> end) >> end >> >> julia> @awhen([1, 2, 3], it[2]) # workds fine >> 2 >> julia> @awhen(nothing, it[2]) # workds fine >> >> julia> @awhen([1, 2, 3], x = 1, it[x]) # :(, failed >> >> ERROR: unsupported or misplaced expression kw >> >> >> julia> macroexpand(:@awhen([1,2,3], x = 1, it[x])) >> quote # none, line 3: >> let it = [1,2,3] # line 4: >> if it != nothing # line 5: >> x=1 >> it[x] >> end >> end >> end >> >> >> Have no idea how to let this worked... >> Please help me, thanks. >> >
