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Elif without If not recognized in nested If #500

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tpwrules opened this issue Sep 18, 2020 · 1 comment
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Elif without If not recognized in nested If #500

tpwrules opened this issue Sep 18, 2020 · 1 comment
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bug
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0.3

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@tpwrules
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tpwrules commented Sep 18, 2020 •
edited by whitequark

The following code snippet does not produce a syntax error and in fact generates without any complaints at all (not sure what the effect is):

s = Signal()
with m.If(1):
    with m.Elif(2):
        m.d.comb += s.eq(3)

I would expect it to raise nmigen.hdl.dsl.SyntaxError: Elif without preceding If like the following snippet does:

s = Signal()
with m.Elif(4):
    m.d.comb += s.eq(5)
@whitequark whitequark added the bug label Sep 21, 2020
@whitequark whitequark added this to the 0.3 milestone Sep 21, 2020
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whitequark commented Oct 22, 2020 •
edited

The effect is this:

(switch
  (cat (sig b) (sig a))
   (case -1 (eq (sig s) (const 1'd1)))
   (case 1- ))

so basically (converting back to the notation in your example):

with m.If(2):
    m.d.comb += s.eq(3)

which is pretty weird indeed, and most certainly not remotely what you intended. Great catch!

@tpwrules tpwrules mentioned this issue May 11, 2021
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