(macro) display the type-alist from the current context

(type-alist t t) ; display type-alist based on both conclusion and governors
type-alist       ; same as (type-alist nil t) -- governors only
(type-alist nil) ; same as (type-alist nil t) -- governors only
(type-alist t)   ; same as (type-alist t nil) -- conclusion only
(type-alist nil nil) ; display type-alist without considering
                     ; conclusion or governors

General Form: (type-alist &optional concl-flg govs-flg)

where if govs-flg is omitted, it defaults to (not concl-flg).

Display the current assumptions as a type-alist. Note that this display includes the result of forward chaining.

There are two basic reasons contemplated for using this command.

1. The theorem prover has failed (either outside the proof-checker or using a proof-checker command such as bash or reduce and you want to debug by getting an idea of what the prover knows about the context.

a. You really are interested in the context for the current term. Include hypotheses and governors (i.e., accounting for tests of surrounding if-expressions that must be true or false) but not the current conclusion (which the theorem prover's heuristics would generally ignore for contextual information). Command:
(type-alist nil t) ; equivalently, type-alist or (type-alist nil)

b. You are not thinking in particular about the current term; you just want to get an idea of the context that the prover would build at the top-level, for forward-chaining. Incorporate the conclusion but not the governors. Command:
(type-alist t nil) ; equivalently, (type-alist t)

2. You intend to use one of the proof-checker-commands that does simplification, such as s or x, and you want to see the context. Then include the surrounding if-term governors but not the goal's conclusion. Command:
(type-alist nil t) ; equivalently, type-alist or (type-alist nil)

See type-set (also see type-prescription) for information about ACL2's type system, which can assist in understanding the output of the type-alist command.