[Agda] Absurd question
m.escardo at cs.bham.ac.uk
Thu May 23 21:09:19 CEST 2013
I have a problem with absurdity in Agda, which I can solve in an
undesirable way, which forces me to change several definitions.
I would like to both understand what the problem is, and why the
desirable way doesn't work.
I have three types X,Y,Z, whose definition I omit here. I can define,
using absurd patterns,
x : X
x = \a ()
y : Y
y : \()
z : Z
z : \()
These are types which have a parameter n:N that happens to be zero and
so they trivialize in this special case, as they have occurrences of Fin
n in their definitions.
Now I have three holes in a definition (of a fourth type), reported to
have types X,Y,Z. I can fill the holes with x,y,z, and the definition
But if I instead fill the holes with \a (), \(), and \(), expanding the
definitions of x,y,z, then type-checking fails.
Moreover, if just one of the three holes is filled with the
corresponding term, type checking still fails.
Additionally, if I ask the emacs interface to fill the wholes with
ctrl-c-a, this succeeds, with expressions containing the string
"absurd". But then the resulting expression doesn't type check.
And there is a more annoying fact. I have previous definition of
something else that uses \() and does type check. However, when I use
it, things fail. I instead need to use the same definition with replaced
\() by y.
This is very mysterious to me.
I didn't manage to distil a simple instance of this to reproduce here.
But if you are brave enough, you can search for "AGDA PROBLEM" in any of
the two following links:
Help is appreciated.
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