Support \brace and \brack (#1453)

* Support \brace and \brack

* Update screenshots

src/functions/genfrac.js

@@ -15,6 +15,7 @@ defineFunction({
         "\\cfrac", "\\dfrac", "\\frac", "\\tfrac",
         "\\dbinom", "\\binom", "\\tbinom",
         "\\\\atopfrac", // can’t be entered directly
+        "\\\\bracefrac", "\\\\brackfrac",   // ditto
     ],
     props: {
         numArgs: 2,
@@ -45,6 +46,16 @@ defineFunction({
                 leftDelim = "(";
                 rightDelim = ")";
                 break;
+            case "\\\\bracefrac":
+                hasBarLine = false;
+                leftDelim = "\\{";
+                rightDelim = "\\}";
+                break;
+            case "\\\\brackfrac":
+                hasBarLine = false;
+                leftDelim = "[";
+                rightDelim = "]";
+                break;
             default:
                 throw new Error("Unrecognized genfrac command");
         }
@@ -272,7 +283,7 @@ defineFunction({
 // immediately by one of the variants above.
 defineFunction({
     type: "infix",
-    names: ["\\over", "\\choose", "\\atop"],
+    names: ["\\over", "\\choose", "\\atop", "\\brace", "\\brack"],
     props: {
         numArgs: 0,
         infix: true,
@@ -289,6 +300,12 @@ defineFunction({
             case "\\atop":
                 replaceWith = "\\\\atopfrac";
                 break;
+            case "\\brace":
+                replaceWith = "\\\\bracefrac";
+                break;
+            case "\\brack":
+                replaceWith = "\\\\brackfrac";
+                break;
             default:
                 throw new Error("Unrecognized infix genfrac command");
         }

test/katex-spec.js

@@ -477,13 +477,17 @@ describe("A frac parser", function() {
     });
 });
 
-describe("An over parser", function() {
+describe("An over/brace/brack parser", function() {
     const simpleOver = "1 \\over x";
     const complexOver = "1+2i \\over 3+4i";
+    const braceFrac = "a+b \\brace c+d";
+    const brackFrac = "a+b \\brack c+d";
 
     it("should not fail", function() {
         expect(simpleOver).toParse();
         expect(complexOver).toParse();
+        expect(braceFrac).toParse();
+        expect(brackFrac).toParse();
     });
 
     it("should produce a frac", function() {
@@ -500,6 +504,22 @@ describe("An over parser", function() {
         expect(parse.type).toEqual("genfrac");
         expect(parse.value.numer).toBeDefined();
         expect(parse.value.denom).toBeDefined();
+
+        const parseBraceFrac = getParsed(braceFrac)[0];
+
+        expect(parseBraceFrac.type).toEqual("genfrac");
+        expect(parseBraceFrac.value.numer).toBeDefined();
+        expect(parseBraceFrac.value.denom).toBeDefined();
+        expect(parseBraceFrac.value.leftDelim).toBeDefined();
+        expect(parseBraceFrac.value.rightDelim).toBeDefined();
+
+        const parseBrackFrac = getParsed(brackFrac)[0];
+
+        expect(parseBrackFrac.type).toEqual("genfrac");
+        expect(parseBrackFrac.value.numer).toBeDefined();
+        expect(parseBrackFrac.value.denom).toBeDefined();
+        expect(parseBrackFrac.value.leftDelim).toBeDefined();
+        expect(parseBrackFrac.value.rightDelim).toBeDefined();
     });
 
     it("should create a numerator from the atoms before \\over", function() {
@@ -567,6 +587,16 @@ describe("An over parser", function() {
     });
 });
 
+describe("A infix builder", function() {
+    it("should not fail", function() {
+        expect("a \\over b").toBuild();
+        expect("a \\atop b").toBuild();
+        expect("a \\choose b").toBuild();
+        expect("a \\brace b").toBuild();
+        expect("a \\brack b").toBuild();
+    });
+});
+
 describe("A sizing parser", function() {
     const sizeExpression = "\\Huge{x}\\small{x}";
 

test/screenshotter/ss_data.yaml

@@ -113,7 +113,11 @@ ExtensibleArrows: |
         \xrightleftharpoons[ab]{ABC} + \xhookrightarrow[ab]{ABC} \\
         \xtwoheadrightarrow{ABC} + \frac{\xrightarrow[ab]{ABC}}{\xrightarrow[ab]{ABC}} + \left\lvert\xrightarrow[ab]{ABC}\right\rvert
     \end{array}
-FractionTest: \dfrac{a}{b}\frac{a}{b}\tfrac{a}{b}\;-\dfrac12\;1\tfrac12\;{1 \atop 2}\; \cfrac{1}{1+\cfrac{1}{x}}
+FractionTest: |
+    \begin{array}{l}
+        \dfrac{a}{b}\frac{a}{b}\tfrac{a}{b}\;-\dfrac12\;1\tfrac12\;{1 \atop 2}\; \cfrac{1}{1+\cfrac{1}{x}} \\[2.5em]
+        {a \brace b} \; {a \brack b}
+    \end{array}
 Functions: \sin\cos\tan\ln\log
 Gathered: |
     \begin{gathered}