Runtime evaluation/In an environment: Difference between revisions
Runtime evaluation/In an environment (view source)
Revision as of 00:53, 18 October 2018
, 5 years agoAdd Factor example
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=={{header|Factor}}==
Being a stack-based language, there is no need to bind data stack objects to a variable name. This is the idiomatic way to do it, with <code>eval</code> referencing what it needs from the data stack:
<lang factor>USE: eval
: eval-bi@- ( a b program -- n )
tuck [ ( y -- z ) eval ] 2bi@ - ;</lang>
<lang factor>IN: scratchpad 9 4 "dup *" eval-bi@- .
65</lang>
Also note that, since programs are first-class denizens in Factor, the use cases for <code>eval</code> are few. Normally, you would pass in a program as a quotation:
<lang factor>: bi@- ( a b quot -- n ) bi@ - ; inline</lang>
<lang factor>IN: scratchpad 9 4 [ dup * ] bi@- .
65</lang>
However, to be pedantic about it, we can adhere to the letter of the task. Note that although we are using a dynamic variable for x, it exists in a temporary, non-global namespace. As far as I can tell, <code>eval</code> is unaware of surrounding lexical scope.
<lang factor>SYMBOL: x
: eval-with-x ( a b program -- n )
tuck
[ [ x ] dip [ ( -- y ) eval ] curry with-variable ] 2bi@ - ;</lang>
<lang factor>IN: scratchpad "x get dup * " eval-with-x .
65</lang>
=={{header|Forth}}==
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