expression-parser 

An expression evaluator written in typescript with the goal to support SQL like WHERE clauses.

Installation

``
npm install --save @valraiso-esf/expression-parser
`

Supported Operations and Functions

$3

- +
- -
- *
- /

$3

- =
- <>
- >
- >=
- <=

$3

- and
- or

$3

- IS NULL
- IS NOT NULL
- BETWEEN [NUMBER] AND [NUMBER]
- CASE WHEN expression THEN expression [WHEN expression] [ELSE expression] END

$3

Currently only function that is evaluated is the LENGTH(variable) function but supports function calls at the parser level so it is fairly easy to add more SQL functions.

Examples

`js

/ Basic Math /
evaluate('1+2'));
// 3
evaluate('10 + 2 * 6'));
// 22
evaluate('100 * 2 + 12'));
// 212
evaluate('100 * ( 2 + 12 )'));
// 1400
evaluate('100 * ( 2 + 12 ) / 14'));
// 100


/ Basic Math With Variable Substitution/

const context = {
a: 1, b: 2, c: 10, d: 6, e: 100, f: 12, g: 14,
};

evaluateObject('a+b', context));
// 3
evaluateObject('c + b * d', context));
// 22
evaluateObject('e * b + f', context));
// 212
evaluateObject('e * ( b + f )', context));
// 1400
evaluateObject('e * ( b + f ) / g', context));
// 100

/ Other Operations /
const val: any = { a: null };
evaluateObject('a is not null and length(a) between 4 and 10', val);
// false
const val = { a: '123' };
evaluateObject('a is not null and length(a) between 4 and 10', val);
// false
const val = { a: '1234' };
evaluateObject('a is not null and length(a) between 4 and 10', val);
// true
const val = { a: '1234567890' };
evaluateObject('a is not null and length(a) between 4 and 10', val);
// true
const val = { a: '12345678901' };
evaluateObject('a is not null and length(a) between 4 and 10', val);
// false
const val: any = { a: 1, b: 1 };
evaluateObject('a is not null and b is not null', val);
// true
evaluateObject('a is not null and b is null', val);
// false
const val = { a: 1, b: null };
evaluateObject('a is not null and b is null', val);
// true
const val = { a: 1, b: 1 };
evaluateObject('a=b', val));
// true
evaluateObject('a>b', val));
// false
evaluateObject('a// false
const val = { a: 1, b: 2 };
evaluateObject('a=b', val);
// false
evaluateObject('a>b', val);
// false
evaluateObject('a// true

const val = { a: 1, b: 3 };
evaluateObject('case when a > 1 then true else false end', val);
// false
const val = { a: 2, b: 3 };
evaluateObject('case when a > 1 then true else false end', val);
// true
val = { a: 2, b: 3 };
evaluateObject('case when a = 1 then 1 when a = 2 then 1 else false end', val);
// 1
evaluateObject('case when a = 1 then 1 when a = 2 then 2 else 3 end', val);
// 2
evaluateObject('case when a = 1 then 1 when a = 3 then 3 else 2 end', val);
// 2
const rule = case
when light = 'Green' then 'Go'
when light = 'Yellow' then 'Should Stop'
when light = 'Red' then 'Stop'
else 'Invalid State' end;
val = { light: 'Yellow' };
evaluateObject(rule, val))
// 'Should Stop'
val = { light: 'Green' };
evaluateObject(rule, val))
// 'Go'
val = { light: 'Red' };
evaluateObject(rule, val))
// 'Stop'
val = { light: 'Blue' };
evaluateObject(rule, val))
// 'Invalid State'

`

Sample AST

`json
//Expression: a is not null and length(a) between 4 and 10
{
"operator": "and",
"left": {
"operator": "<>",
"left": {
"name": "a",
"type": "IdentifierExpression"
},
"right": {
"value": null,
"type": "ValueExpression"
},
"type": "BinaryExpression"
},
"right": {
"operator": "and",
"left": {
"operator": ">=",
"left": {
"name": "length",
"args": [
{
"name": "a",
"type": "IdentifierExpression"
}
],
"type": "FunctionCallExpression"
},
"right": {
"value": 4,
"type": "ValueExpression"
},
"type": "BinaryExpression"
},
"right": {
"operator": "<=",
"left": {
"name": "length",
"args": [
{
"name": "a",
"type": "IdentifierExpression"
}
],
"type": "FunctionCallExpression"
},
"right": {
"value": 10,
"type": "ValueExpression"
},
"type": "BinaryExpression"
},
"type": "BinaryExpression"
},
"type": "BinaryExpression"
}
`

Test Coverage

`
13 specs, 0 failures
Finished in 0.069 seconds
Randomized with seed 62175 (jasmine --random=true --seed=62175)
--------------|---------|----------|---------|---------|-----------------------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
--------------|---------|----------|---------|---------|-----------------------------------
All files | 93.24 | 83.33 | 92.73 | 93.19 |
ast.ts | 89.66 | 100 | 90 | 90 | 16-18
evaluator.ts | 85 | 69.23 | 100 | 84.21 | 14,18,27,47-49,64
lexer.ts | 99.04 | 98 | 100 | 99.03 | 86
parser.ts | 89.89 | 70 | 89.47 | 89.41 | 83,91,103,121,133,137,144,181,184
token.ts | 97.06 | 100 | 75 | 96.97 | 44
--------------|---------|----------|---------|---------|-----------------------------------
``