Lean.Meta.Check

This is not the Kernel type checker, but an auxiliary method for checking whether terms produced by tactics and isDefEq are type correct.

source

def Lean.Meta.throwLetTypeMismatchMessage {α : Type} (fvarId : Lean.FVarId) :

Lean.MetaM α

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Instances For

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def Lean.Meta.addPPExplicitToExposeDiff (a : Lean.Expr) (b : Lean.Expr) :

Lean.MetaM (Lean.Expr × Lean.Expr)

Given two expressions a and b, this method tries to annotate terms with pp.explicit := true to expose "implicit" differences. For example, suppose a and b are of the form

@HashMap Nat Nat eqInst hasInst1
@HashMap Nat Nat eqInst hasInst2

By default, the pretty printer formats both of them as HashMap Nat Nat. So, counterintuitive error messages such as

error: application type mismatch
  HashMap.insert m
argument
  m
has type
  HashMap Nat Nat
but is expected to have type
  HashMap Nat Nat

would be produced. By adding pp.explicit := true, we can generate the more informative error

error: application type mismatch
  HashMap.insert m
argument
  m
has type
  @HashMap Nat Nat eqInst hasInst1
but is expected to have type
  @HashMap Nat Nat eqInst hasInst2

Remark: this method implements a simple heuristic, we should extend it as we find other counterintuitive error messages.

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