Implement binom.

protosse · Jul 16, 2016 · ecdded7 · ecdded7
1 parent c424990
commit ecdded7
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diff --git a/iosMath/lib/MTMathListBuilder.m b/iosMath/lib/MTMathListBuilder.m
@@ -271,6 +271,14 @@ - (MTMathAtom*) atomForCommand:(NSString*) command
         frac.numerator = [self buildInternal:true];
         frac.denominator = [self buildInternal:true];
         return frac;
+    } else if ([command isEqualToString:@"binom"]) {
+        // A binom command has 2 arguments
+        MTFraction* frac = [[MTFraction alloc] initWithRule:NO];
+        frac.numerator = [self buildInternal:true];
+        frac.denominator = [self buildInternal:true];
+        frac.leftDelimiter = @"(";
+        frac.rightDelimiter = @")";
+        return frac;
     } else if ([command isEqualToString:@"sqrt"]) {
         // A sqrt command with one argument
         MTRadical* rad = [MTRadical new];

diff --git a/iosMathTests/MTMathListBuilderTest.m b/iosMathTests/MTMathListBuilderTest.m
@@ -746,6 +746,41 @@ - (void) testBrace
     XCTAssertEqualObjects(latex, @"{n \\brace k}", @"%@", desc);
 }
 
+- (void) testBinom
+{
+    NSString *str = @"\\binom{n}{k}";
+    MTMathList* list = [MTMathListBuilder buildFromString:str];
+    NSString* desc = [NSString stringWithFormat:@"Error for string:%@", str];
+
+    XCTAssertNotNil(list, @"%@", desc);
+    XCTAssertEqualObjects(@(list.atoms.count), @1, @"%@", desc);
+    MTFraction* frac = list.atoms[0];
+    XCTAssertEqual(frac.type, kMTMathAtomFraction, @"%@", desc);
+    XCTAssertEqualObjects(frac.nucleus, @"", @"%@", desc);
+    XCTAssertFalse(frac.hasRule);
+    XCTAssertEqualObjects(frac.rightDelimiter, @")");
+    XCTAssertEqualObjects(frac.leftDelimiter, @"(");
+
+    MTMathList *subList = frac.numerator;
+    XCTAssertNotNil(subList, @"%@", desc);
+    XCTAssertEqualObjects(@(subList.atoms.count), @1, @"%@", desc);
+    MTMathAtom *atom = subList.atoms[0];
+    XCTAssertEqual(atom.type, kMTMathAtomVariable, @"%@", desc);
+    XCTAssertEqualObjects(atom.nucleus, @"n", @"%@", desc);
+
+    atom = list.atoms[0];
+    subList = frac.denominator;
+    XCTAssertNotNil(subList, @"%@", desc);
+    XCTAssertEqualObjects(@(subList.atoms.count), @1, @"%@", desc);
+    atom = subList.atoms[0];
+    XCTAssertEqual(atom.type, kMTMathAtomVariable, @"%@", desc);
+    XCTAssertEqualObjects(atom.nucleus, @"k", @"%@", desc);
+
+    // convert it back to latex (binom converts to choose)
+    NSString* latex = [MTMathListBuilder mathListToString:list];
+    XCTAssertEqualObjects(latex, @"{n \\choose k}", @"%@", desc);
+}
+
 static NSArray* getTestDataParseErrors() {
     return @[
               @[@"}a", @(MTParseErrorMismatchBraces)],