Add support for scientific notation with 'e' and 'E'

src/lexer.ts

@@ -59,6 +59,7 @@ var type3Asterick: Allowed = {
 }; // type_5:true,type_7:true,type_23
 var type6: Allowed = {
   1: true,
+  3: true,
 };
 var newAr = [
   [],
@@ -83,6 +84,7 @@ var newAr = [
     "P",
     "C",
     "e",
+    "E",
     "0",
     ".",
     ",",
@@ -279,6 +281,33 @@ export const lex = function (this: Mexp, inp: string, tokens?: Token[]) {
     if (allowed[cType] !== true) {
       throw new Error(cToken + " is not allowed after " + prevKey);
     }
+    if (
+      (cToken === "e" || cToken === "E") &&
+      pre.type === tokenTypes.NUMBER &&
+      i < nodes.length - 1
+    ) {
+      var next = nodes[i + 1];
+      var isScientific = false;
+      if (next.type === tokenTypes.NUMBER) {
+        isScientific = true;
+      } else if (
+        (next.token === "+" || next.token === "-") &&
+        i < nodes.length - 2 &&
+        nodes[i + 2].type === tokenTypes.NUMBER
+      ) {
+        isScientific = true;
+      }
+      if (isScientific) {
+        pre.value += "e";
+        if (next.type !== tokenTypes.NUMBER) {
+          pre.value += next.token;
+          i++;
+        }
+        allowed = type6;
+        asterick = empty;
+        continue;
+      }
+    }
     if (asterick[cType] === true) {
       cType = tokenTypes.BINARY_OPERATOR_HIGH_PRECENDENCE;
       cEv = this.math.mul;

src/token.ts

@@ -67,6 +67,7 @@ export const createTokens = (mexp: Mexp) => {
 		{ token: 'sinh', show: 'sinh', type: 0, value: mexp.math.sinh },
 		{ token: 'asinh', show: 'asinh', type: 0, value: mexp.math.asinh },
 		{ token: 'e', show: 'e', type: 3, value: 'E' },
+		{ token: 'E', show: 'E', type: 3, value: 'E' },
 		{ token: 'log', show: ' log', type: 0, value: mexp.math.log },
 		{ token: '0', show: '0', type: 1, value: '0' },
 		{ token: '.', show: '.', type: 6, value: '.' },

test/scientific-notation.js

@@ -0,0 +1,39 @@
+var assert = require('assert')
+var Mexp = require('../dist/es/index.js')
+var mexp = new Mexp()
+
+describe('Scientific notation', function () {
+    it('should parse 1e-7 correctly', function () {
+        assert.equal(mexp.eval('1e-7'), 0.0000001)
+    })
+    it('should parse 1e+7 correctly', function () {
+        assert.equal(mexp.eval('1e+7'), 10000000)
+    })
+    it('should parse 1e7 correctly', function () {
+        assert.equal(mexp.eval('1e7'), 10000000)
+    })
+    it('should parse 1.5e-2 correctly', function () {
+        assert.equal(mexp.eval('1.5e-2'), 0.015)
+    })
+    it('should parse capital E correctly', function () {
+        assert.equal(mexp.eval('1E-7'), 0.0000001)
+    })
+    it('should parse complex expressions with scientific notation', function () {
+        assert.equal(mexp.eval('1e-7*10'), 0.000001)
+    })
+    it('should parse scientific notation with addition', function () {
+        assert.equal(mexp.eval('1e3+500'), 1500)
+    })
+    it('should parse scientific notation in functions', function () {
+        assert.equal(mexp.eval('log(1e2)'), 2)
+    })
+    it('should handle zero exponent correctly', function () {
+        assert.equal(mexp.eval('5e0'), 5)
+    })
+    it('should still support Euler constant e', function () {
+        assert.equal(mexp.eval('e'), Math.E)
+    })
+    it('should distinguish between Euler constant e and scientific notation', function () {
+        assert.equal(mexp.eval('e-1e-1+e'), Math.E - 0.1 + Math.E)
+    })
+})