diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 49 |
1 files changed, 44 insertions, 5 deletions
@@ -18139,8 +18139,9 @@ If is absent, the global environment is used. The .meta env -argument is used for macro-expanding -.metn form . +argument is used for fully expanding +.meta form +prior to analyzing. Currently, .code constantp @@ -18154,10 +18155,48 @@ These symbols are the keyword symbols, and the symbols and .codn nil . -In the future, +Additionally, +.code constantp +returns true for a compound form, or a DWIM form, whose symbol is +the member of a set a large number of constant-foldable library functions, +and whose arguments are, recursively, +.code constantp +expressions for the same environment. The arithmetic functions +are members of this set. + +For all other inputs, +.code constantp +returns +.codn nil . + +Note: some uses of .code constantp -will be able to recognize more constant forms, such as calls to certain -functions whose arguments are constant forms. +require manual expansion. + +.TP* Examples: + +.verb + (constantp nil) -> t + (constantp t) -> t + (constantp :key) -> t + (constantp :) -> t + (constantp 'a) -> nil + (constantp 42) -> t + + (constantp '(+ 2 2 [* 3 (/ 4 4)]) -> t + + ;; symacrolet form expands to 42, which is constant + (constantp '(symacrolet ((a 42)) a)) + + (defmacro cp (:env e arg) + (constantp arg e)) + + ;; macro call (cp 'a) is replaced by t because + ;; the symbol a expands to (+ 2 2) in the given environment, + ;; and so (* a a) expands to (* (+ 2 2) (+ 2 2)) which is constantp. + (symacrolet ((a (+ 2 2))) + (cp '(* a a))) -> t +.brev .coNP Function @ make-env .synb |