Parse math expressions to a useful AST, with built-in compilers for:
- creating a sanitized executable javascript function
- creating a function that returns a value for every node of the AST when executed
- echoes back the original expression if parsing succeeds
The compilers are provided for convenience, an will not be pulled into a build unless you specifically require them. The AST is pretty easy to walk if you build your own compiler -- the echo compiler only requires seven lines of code to implement
$ npm install expression-parser
and also get the raw js generated for the function
> var mkFunc = require('expression-parser/func'); > var expressionFunc = compile('c*sin(2*t)+1'); > expressionFunc({c: 0.5}); 0.9999999999999999 > mkFunc.express('sqrt(x^2 + y^2)') '(Math.sqrt((Math.pow(symbols["x"],2.0)+Math.pow(symbols["y"],2.0))))'
Note that everything in the global Math is made available by the built-in function compiler, and it is assumed that the global Math assumed available by its express function.
and then echo back the original expression with just the AST
> var parse = require('expression-parser/parse'); > var ast = parse('sin(t)^2 + cos(t)^2'); > ast { id: 0, type: 'ASTNode', node: 'expr', template: '#', children: [ { id: 1, type: 'ASTNode', node: 'func', template: '# +#', children: [Object], options: [Object] } ], options: {} } > console.log(JSON.stringify(ast, null, 2)); // print out the whole thing { "id": 0, "type": "ASTNode", "node": "expr", "template": "#", "children": [ { "id": 1, "type": "ASTNode", "node": "func", "template": "# +#", "children": [ { "id": 2, "type": "ASTNode", "node": "func", "template": "#^#", "children": [ { "id": 3, "type": "ASTNode", "node": "func", "template": "sin(#)", "children": [ { "id": 4, "type": "ASTNode", "node": "name", "template": "t", "children": [], "options": { "key": "t" } } ], "options": { "key": "sin" } }, { "id": 5, "type": "ASTNode", "node": "literal", "template": "2", "children": [], "options": { "value": 2 } } ], "options": { "key": "pow" } }, { "id": 6, "type": "ASTNode", "node": "func", "template": "#^#", "children": [ { "id": 7, "type": "ASTNode", "node": "func", "template": " cos(#)", "children": [ { "id": 8, "type": "ASTNode", "node": "name", "template": "t", "children": [], "options": { "key": "t" } } ], "options": { "key": "cos" } }, { "id": 9, "type": "ASTNode", "node": "literal", "template": "2", "children": [], "options": { "value": 2 } } ], "options": { "key": "pow" } } ], "options": { "key": "sum" } } ], "options": {} } > var valuer = require('expression-parser/values'); > values.fromAST(ast)({t: 0}) [ 1, 1, 0, 0, 0, 2, 1, 1, 0, 2 ] > var echoer = require('expression-parser/echo'); > echoer.fromAST(ast); 'sin(t)^2 + cos(t)^2'
New AST node design:
{ id: 0, type: 'ASTNode', node: 'expr', template: '#', children: [], options: {} }
idmust be uniquetypemust be a valid node typeoptionscontains different properties depending on the node type
options:
{}
options:
{ key: 'funcName' }
Infix functions should be normal function nodes. Here are some examples for + with 2 or 3 operands:
{ id: 0, type: 'ASTNode', node: 'func',u template: '# + # + #', children: [someNode, anotherNode, andAnother], options: { key: 'sum' } }
Normal functions can take multiple arguments
{ id: 0, type: 'ASTNode', node: 'func', template: 'min(#, #)', children: [someNode, anotherNode], options: { key: 'min' } }
options:
{ key: 'varName' }
options:
{ value: 1 }