mathlib documentation

tactic.where

The where command

When working in a Lean file with namespaces, parameters, and variables, it can be confusing to identify what the current "parser context" is. The command #where identifies and prints information about the current location, including the active namespace, open namespaces, and declared variables.

It is a bug for #where to incorrectly report this information (this was not formerly the case); please file an issue on GitHub if you observe a failure.

Assigns a priority to each binder for determining the order in which variables are traced.

The relation on binder priorities.

def where.select_for_which {α β γ : Type} (p : α → β × γ) [decidable_eq β] :
β → list αlist γ × list α

Selects the elements of the given list α which under the image of p : α → β × γ have β component equal to b'. Returns the γ components of the selected elements under the image of p, and the elements of the original list α which were not selected.

Equations
meta def where.collect_by {α β γ : Type} (l : list α) (p : α → β × γ) [decidable_eq β] :
list × list γ)

Returns the elements of l under the image of p, collecting together elements with the same β component, deleting duplicates.

Sort the variables by their priority as defined by where.binder_priority.

Separate out the names of implicit variables (commonly instances with no name).

Format an individual variable definition for printing.

Turn a list of triples of variable names, binder info, and types, into a pretty list.

get_open_namespaces ns returns a list of the open namespaces, given that we are currently in the namespace ns (which we do not include).

#where output helper which traces the current namespace.

#where output helper which traces the open namespaces.

#where output helper which traces the variables.

#where output helper which traces the includes.

#where output helper which traces the namespace end.

#where output main function.

When working in a Lean file with namespaces, parameters, and variables, it can be confusing to identify what the current "parser context" is. The command #where identifies and prints information about the current location, including the active namespace, open namespaces, and declared variables.

It is a bug for #where to incorrectly report this information (this was not formerly the case); please file an issue on GitHub if you observe a failure.