Simplify the arithmetics example grammar

The arithmetics example grammar is the first thing everyone sees in the
online editor at the PEG.js website, but it begins with a complicated
|combine| function in the initializer. Without understanding it it is
impossible to understand code in the actions. This may be a barrier to
learning how PEG.js works.

This commit removes the |combine| function and gets rid of the whole
initializer, removing the learning obstacle and streamlining action
code. The only cost is a slight code duplication.
redux
David Majda 9 years ago
parent 69a0f769fc
commit 10d7a6aded

@ -5,32 +5,28 @@
* Accepts expressions like "2 * (3 + 4)" and computes their value.
*/
{
function combine(first, rest, combiners) {
var result = first, i;
for (i = 0; i < rest.length; i++) {
result = combiners[rest[i][1]](result, rest[i][3]);
}
return result;
}
}
Expression
= first:Term rest:(_ ("+" / "-") _ Term)* {
return combine(first, rest, {
"+": function(left, right) { return left + right; },
"-": function(left, right) { return left - right; }
});
var result = first, i;
for (i = 0; i < rest.length; i++) {
if (rest[i][1] === "+") { result += rest[i][3]; }
if (rest[i][1] === "-") { result -= rest[i][3]; }
}
return result;
}
Term
= first:Factor rest:(_ ("*" / "/") _ Factor)* {
return combine(first, rest, {
"*": function(left, right) { return left * right; },
"/": function(left, right) { return left / right; }
});
var result = first, i;
for (i = 0; i < rest.length; i++) {
if (rest[i][1] === "*") { result *= rest[i][3]; }
if (rest[i][1] === "/") { result /= rest[i][3]; }
}
return result;
}
Factor

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