leanprover / leanprover/reference-manual
fallback in pattern match
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Description
What question should the reference manual answer?
I couldn't find an explanation for the syntax below in the manual. I guess the notation means let pattern := value | fallback
#eval do
let a :: as := [1,2,3] | none
return as.map (a + ·)
The syntax let pattern ← value | fallback didn't work. Would it make sense? In which situation? This construction is only allowed inside the do notation, right?
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Research direction
In the reference manual, start by locating the section covering do notation and pattern matching, then compare it with the supplied let a :: as := ... | none example. Document what the fallback syntax means, whether the arrow form is supported, and the contexts where the construction is allowed; done when the manual answers these questions.
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Assessment
- Domain
- documentation
- Issue type
- Documentation
- Difficulty
- 2/5
- Estimated time
- 1-3 hours
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100