delay(expr, env=.GlobalEnv)
expr
| an expression. |
env
| an evaluation environment |
delay
creates a promise to evaluate the given
expression in the specifies environment if its value is requested.
This provides direct access to lazy evaluation mechanism
used by R for the evaluation of (interpreted) functions.
This is an experimental feature and its addition is purely for evaluation purposes.
delay
can be assigned
without forcing its evaluation, but any further accesses
will cause evaluation.x <- delay({ for(i in 1:7) cat("yippee!\n") 10 }) x^2#- yippee x^2#- simple number