@tannin/plural-forms
Version:
Compiles a function to compute the plural forms index for a given value
287 lines (258 loc) • 6.09 kB
JavaScript
var pluralForms = (function () {
'use strict';
var PRECEDENCE, OPENERS, TERMINATORS, PATTERN;
/**
* Operator precedence mapping.
*
* @type {Object}
*/
PRECEDENCE = {
'(': 9,
'!': 8,
'*': 7,
'/': 7,
'%': 7,
'+': 6,
'-': 6,
'<': 5,
'<=': 5,
'>': 5,
'>=': 5,
'==': 4,
'!=': 4,
'&&': 3,
'||': 2,
'?': 1,
'?:': 1,
};
/**
* Characters which signal pair opening, to be terminated by terminators.
*
* @type {string[]}
*/
OPENERS = [ '(', '?' ];
/**
* Characters which signal pair termination, the value an array with the
* opener as its first member. The second member is an optional operator
* replacement to push to the stack.
*
* @type {string[]}
*/
TERMINATORS = {
')': [ '(' ],
':': [ '?', '?:' ],
};
/**
* Pattern matching operators and openers.
*
* @type {RegExp}
*/
PATTERN = /<=|>=|==|!=|&&|\|\||\?:|\(|!|\*|\/|%|\+|-|<|>|\?|\)|:/;
/**
* Given a C expression, returns the equivalent postfix (Reverse Polish)
* notation terms as an array.
*
* If a postfix string is desired, simply `.join( ' ' )` the result.
*
* @example
*
* ```js
* import postfix from '@tannin/postfix';
*
* postfix( 'n > 1' );
* // ⇒ [ 'n', '1', '>' ]
* ```
*
* @param {string} expression C expression.
*
* @return {string[]} Postfix terms.
*/
function postfix( expression ) {
var terms = [],
stack = [],
match, operator, term, element;
while ( ( match = expression.match( PATTERN ) ) ) {
operator = match[ 0 ];
// Term is the string preceding the operator match. It may contain
// whitespace, and may be empty (if operator is at beginning).
term = expression.substr( 0, match.index ).trim();
if ( term ) {
terms.push( term );
}
while ( ( element = stack.pop() ) ) {
if ( TERMINATORS[ operator ] ) {
if ( TERMINATORS[ operator ][ 0 ] === element ) {
// Substitution works here under assumption that because
// the assigned operator will no longer be a terminator, it
// will be pushed to the stack during the condition below.
operator = TERMINATORS[ operator ][ 1 ] || operator;
break;
}
} else if ( OPENERS.indexOf( element ) >= 0 || PRECEDENCE[ element ] < PRECEDENCE[ operator ] ) {
// Push to stack if either an opener or when pop reveals an
// element of lower precedence.
stack.push( element );
break;
}
// For each popped from stack, push to terms.
terms.push( element );
}
if ( ! TERMINATORS[ operator ] ) {
stack.push( operator );
}
// Slice matched fragment from expression to continue match.
expression = expression.substr( match.index + operator.length );
}
// Push remainder of operand, if exists, to terms.
expression = expression.trim();
if ( expression ) {
terms.push( expression );
}
// Pop remaining items from stack into terms.
return terms.concat( stack.reverse() );
}
/**
* Operator callback functions.
*
* @type {Object}
*/
var OPERATORS = {
'!': function( a ) {
return ! a;
},
'*': function( a, b ) {
return a * b;
},
'/': function( a, b ) {
return a / b;
},
'%': function( a, b ) {
return a % b;
},
'+': function( a, b ) {
return a + b;
},
'-': function( a, b ) {
return a - b;
},
'<': function( a, b ) {
return a < b;
},
'<=': function( a, b ) {
return a <= b;
},
'>': function( a, b ) {
return a > b;
},
'>=': function( a, b ) {
return a >= b;
},
'==': function( a, b ) {
return a === b;
},
'!=': function( a, b ) {
return a !== b;
},
'&&': function( a, b ) {
return a && b;
},
'||': function( a, b ) {
return a || b;
},
'?:': function( a, b, c ) {
if ( a ) {
throw b;
}
return c;
},
};
/**
* Given an array of postfix terms and operand variables, returns the result of
* the postfix evaluation.
*
* @example
*
* ```js
* import evaluate from '@tannin/evaluate';
*
* // 3 + 4 * 5 / 6 ⇒ '3 4 5 * 6 / +'
* const terms = [ '3', '4', '5', '*', '6', '/', '+' ];
*
* evaluate( terms, {} );
* // ⇒ 6.333333333333334
* ```
*
* @param {string[]} postfix Postfix terms.
* @param {Object} variables Operand variables.
*
* @return {*} Result of evaluation.
*/
function evaluate( postfix, variables ) {
var stack = [],
i, j, args, getOperatorResult, term, value;
for ( i = 0; i < postfix.length; i++ ) {
term = postfix[ i ];
getOperatorResult = OPERATORS[ term ];
if ( getOperatorResult ) {
// Pop from stack by number of function arguments.
j = getOperatorResult.length;
args = Array( j );
while ( j-- ) {
args[ j ] = stack.pop();
}
try {
value = getOperatorResult.apply( null, args );
} catch ( earlyReturn ) {
return earlyReturn;
}
} else if ( variables.hasOwnProperty( term ) ) {
value = variables[ term ];
} else {
value = +term;
}
stack.push( value );
}
return stack[ 0 ];
}
/**
* Given a C expression, returns a function which can be called to evaluate its
* result.
*
* @example
*
* ```js
* import compile from '@tannin/compile';
*
* const evaluate = compile( 'n > 1' );
*
* evaluate( { n: 2 } );
* // ⇒ true
* ```
*
* @param {string} expression C expression.
*
* @return {(variables?:{[variable:string]:*})=>*} Compiled evaluator.
*/
function compile( expression ) {
var terms = postfix( expression );
return function( variables ) {
return evaluate( terms, variables );
};
}
/**
* Given a C expression, returns a function which, when called with a value,
* evaluates the result with the value assumed to be the "n" variable of the
* expression. The result will be coerced to its numeric equivalent.
*
* @param {string} expression C expression.
*
* @return {Function} Evaluator function.
*/
function pluralForms( expression ) {
var evaluate = compile( expression );
return function( n ) {
return +evaluate( { n: n } );
};
}
return pluralForms;
}());