Runtime evaluation/In an environment: Difference between revisions

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(→‎{{header|Octave}}: ++ metafont)
(clarify task: mention not using a global variable, avoid the 'provided code is a function' interpretation)
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{{task}} Given a program in the language representing a function of the variable <var>x</var>, evaluate it with <var>x</var> (or another name if that is not valid syntax) bound to a provided value, then evaluate it again with <var>x</var> bound to another provided value, then subtract the result of the first from the second and return or print it.
{{task}} Given a program in the language with a free variable named <var>x</var> (or another name if that is not valid syntax), evaluate it with <var>x</var> bound to a provided value, then evaluate it again with <var>x</var> bound to another provided value, then subtract the result of the first from the second and return or print it.


Do so in a way which:
Preferably, do so in a way which does not involve string manipulation of source code, and is plausibly extensible to a runtime-chosen set of bindings.
* does not involve string manipulation of source code
* is plausibly extensible to a runtime-chosen set of bindings rather than just <var>x</var>
* does not make <var>x</var> a ''global'' variable
or note that these are impossible.


For more general examples and language-specific details, see [[Eval]].
For more general examples and language-specific details, see [[Eval]].
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=={{header|Metafont}}==
=={{header|Metafont}}==

{{incorrect|Metafont|Either do not use a global variable, or note that this is impossible.}}

<lang metafont>string p;
<lang metafont>string p;
p := "2x + 1";
p := "2x + 1";
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=={{header|Octave}}==
=={{header|Octave}}==

{{incorrect|Octave|Either do not use a global variable, or note that this is impossible.}}


<lang octave>p = "x .* 2";
<lang octave>p = "x .* 2";
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=={{header|PHP}}==
=={{header|PHP}}==

{{incorrect|PHP|Either do not use a global variable, or note that this is impossible.}}


<lang php><?php
<lang php><?php
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=={{header|Tcl}}==
=={{header|Tcl}}==

{{incorrect|Tcl|The code provided should not itself be a function, but have x as a free variable.}}

<lang tcl>package require Tcl 8.5
<lang tcl>package require Tcl 8.5


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