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.

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

MetaM (Expr × Expr)

Given two expressions a and b, this method tries to annotate terms with pp.explicit := true and other pp options 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 simple heuristics; we should extend it as we find other counterintuitive error messages.

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Instances For

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

MetaM α

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def Lean.Meta.mkHasTypeButIsExpectedMsg (givenType expectedType : Expr) (trailing? : Option MessageData := none) (trailingExprs : Array Expr := #[]) :

MetaM MessageData

Return error message "has type{givenType}\nbut is expected to have type{expectedType}" Adds the type’s types unless they are defeq.

If trailing? is non-none, it is appended to the end of the message. This requires modifying the produced message, so prefer specifying trailing? over appending a message to the result of this function. Any expressions appearing in the trailing message should be included in trailingExprs.

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