Add support for subscript

Example:

Input:
┌───────────────────────────┐
│S_n = u_1 + u_2 + ... + u_n│
└───────────────────────────┘
Output:
┌───────────────────────┐
│S  = u  + u  + ... + u │
│ n    1    2          n│
└───────────────────────┘

This fixes issue:
#1

.travis.yml

@@ -8,8 +8,6 @@ script:
   - cd build
   - cmake ..
   - cmake --build .
-  - cat ./CMakeFiles/CMakeOutput.log
-  - cat ./CMakeFiles/CMakeError.log
 
 notifications:
   email: false

src/CMakeLists.txt

@@ -45,7 +45,7 @@ if (Web)
   string(APPEND CMAKE_CXX_FLAGS " -s ASSERTIONS=2")
   string(APPEND CMAKE_CXX_FLAGS " --closure 1")
   string(APPEND CMAKE_CXX_FLAGS " --no-heap-copy")
-  string(APPEND CMAKE_CXX_FLAGS " -s EXPORTED_FUNCTIONS='[\"_translate\"]'")
+  string(APPEND CMAKE_CXX_FLAGS " -s EXPORTED_FUNCTIONS='[\"_translate\", \"_main\"]'")
   string(APPEND CMAKE_CXX_FLAGS " -s EXTRA_EXPORTED_RUNTIME_METHODS='[\"ccall\",\"cwrap\"]'")
 
   option(ADD_GOOGLE_ANALYTICS "Build the static library" ON)

src/translator/math/Math.cpp

@@ -36,15 +36,16 @@ std::vector<Translator::Example> Math::Examples() {
       {"1-fraction", "f(x) = 1 + x / (1 + x)"},
       {"2-square-root", "sqrt(1+sqrt(1+x/2))"},
       {"3-power", "f(x) = 1 + x^2 + x^3 + x^(1+1/2)"},
-      {"4-summation", "sum(i^2,i=0,n) = n^3/2+n^2/2+n/6"},
-      {"5-integral", "int(x^2 * dx ,0,1) = n^3/3"},
-      {"6-product",
+      {"4-subscript", "S_n = u_1 + u_2 + ... + u_n"},
+      {"5-summation", "sum(i^2,i=0,n) = n^3/2+n^2/2+n/6"},
+      {"6-integral", "int(x^2 * dx ,0,1) = n^3/3"},
+      {"7-product",
        "mult(i^2,i=1,n) = (mult(i,i=1,n))^2\n\n\n\nmult(1/2,1,100) = "
        "7.8886091e-31"},
-      {"7-vector", "[a;b] + [c;d] = [a+c; b+d]"},
-      {"8-matrix", "[1,2;3,4] * [x;y] = [1*x+2*y; 3*x+4*y]"},
-      {"9-factorial", "[n;k] = n! / (k! *(n-k)!)"},
-      {"10-Math-symbols",
+      {"8-vector", "[a;b] + [c;d] = [a+c; b+d]"},
+      {"9-matrix", "[1,2;3,4] * [x;y] = [1*x+2*y; 3*x+4*y]"},
+      {"10-factorial", "[n;k] = n! / (k! *(n-k)!)"},
+      {"11-Math-symbols",
        "Alpha + alpha + Digamma + digamma + Kappa + kappa + Omicron \n"
        "omicron + Upsilon + upsilon + Beta + beta + Zeta + zeta + Lambda \n"
        "lambda + Pi + pi + Phi + phi + Gamma + gamma + Eta + eta + Mu + mu \n"
@@ -86,8 +87,7 @@ void Draw::Resize(int new_dim_x, int new_dim_y) {
   dim_x = new_dim_x;
   dim_y = new_dim_y;
 
-  content.resize(dim_y);
-  for (auto& line : content) {
+  content.resize(dim_y); for (auto& line : content) {
     line.resize(dim_x, L' ');
   }
 }
@@ -118,7 +118,7 @@ Draw ComposeVertical(const Draw& top, const Draw& down, int spaces) {
   return composition;
 }
 
-Draw ComposeDiagonal(const Draw& A, const Draw& B) {
+Draw ComposeDiagonalUp(const Draw& A, const Draw& B) {
   Draw composition;
   composition.Append(A, 0, B.dim_y);
   composition.Append(B, A.dim_x, 0);
@@ -129,6 +129,17 @@ Draw ComposeDiagonal(const Draw& A, const Draw& B) {
   return composition;
 }
 
+Draw ComposeDiagonalDown(const Draw& A, const Draw& B) {
+  Draw composition;
+  composition.Append(A, 0, 0);
+  composition.Append(B, A.dim_x, A.dim_y);
+
+  composition.center_x = composition.dim_x / 2;
+  composition.center_y = A.center_y;
+
+  return composition;
+}
+
 Draw WrapWithParenthesis(const Draw& element, Style* style) {
   Draw draw;
   draw.Resize(element.dim_x + 2, element.dim_y);
@@ -253,7 +264,9 @@ Draw Parse(MathParser::FactorContext* context,
   suppress_parenthesis &= (context->valueBang().size() == 1);
   Draw draw = Parse(context->valueBang(0), style, suppress_parenthesis);
   for (int i = 1; i < context->valueBang().size(); ++i) {
-    draw = ComposeDiagonal(draw, Parse(context->valueBang(i), style, false));
+    auto* compose =
+        context->powop(i - 1)->POW() ? ComposeDiagonalUp : ComposeDiagonalDown;
+    draw = compose(draw, Parse(context->valueBang(i), style, false));
   }
   return draw;
 }

src/translator/math/Math.g4

@@ -45,7 +45,7 @@ newlines : EOL+;
 equation : expression (relop expression)* ;
 expression : term (addop term)* ;
 term : factor (mulop factor)* ;
-factor : valueBang (POW valueBang)* ;
+factor : valueBang (powop valueBang)* ;
 valueBang: value | valueBang BANG;
 value : (PLUS | MINUS)? atom ;
 atom : scientific | variable | function | matrix | LPAREN expression RPAREN ;
@@ -57,9 +57,10 @@ matrixLine : expression ( ',' expression ) *;
 relop : EQ | GT | LT | GE | LE;
 addop : PLUS | MINUS ;
 mulop : TIMES | DIV ;
+powop : POW | SUBSCRIPT ;
 VARIABLE : VALID_ID_START VALID_ID_CHAR* | '...' ;
 
-fragment VALID_ID_START : ('a' .. 'z') | ('A' .. 'Z') | '_';
+fragment VALID_ID_START : ('a' .. 'z') | ('A' .. 'Z') ;
 fragment VALID_ID_CHAR : VALID_ID_START | ('0' .. '9') ;
 SCIENTIFIC_NUMBER : NUMBER (E SIGN? NUMBER)? ;
 
@@ -85,6 +86,7 @@ LE : '<=' ;
 EQ : '=' ; 
 POINT : '.' ; 
 POW : '^' ;
+SUBSCRIPT: '_' ;
 EOL : '\r\n' | '\n' ;
 WS : [ \t] + -> skip ; 
 

test/Math/mixed_pow_subscript/input

@@ -0,0 +1,3 @@
+A_2^3
+
+A^2_3

test/Math/mixed_pow_subscript/output

@@ -0,0 +1,7 @@
+  3
+A  
+ 2 
+
+ 2 
+A  
+  3

test/Math/pow/input

@@ -0,0 +1,11 @@
+A^2
+
+A^(1/2)^sqrt(2)
+
+(A^(1/2))^sqrt(2)
+
+A^((1/2)^sqrt(2))
+
+A^421 + 1/2
+
+A^421/2

test/Math/pow/output

@@ -0,0 +1,32 @@
+ 2       
+A        
+
+      _  
+    ╲╱2  
+ ⎛1⎞     
+ ⎜─⎟     
+ ⎝2⎠     
+A        
+
+        _
+      ╲╱2
+⎛ ⎛1⎞⎞   
+⎜ ⎜─⎟⎟   
+⎜ ⎝2⎠⎟   
+⎝A   ⎠   
+
+ ⎛     _⎞
+ ⎜   ╲╱2⎟
+ ⎜⎛1⎞   ⎟
+ ⎜⎜─⎟   ⎟
+ ⎝⎝2⎠   ⎠
+A        
+
+ 421   1 
+A    + ─ 
+       2 
+
+ 421     
+A        
+────     
+  2      

test/Math/subscript/input

@@ -0,0 +1,11 @@
+A_2
+
+A_(1/2)_sqrt(2)
+
+(A_(1/2))_sqrt(2)
+
+A_((1/2)_sqrt(2))
+
+A_421 + 1/2
+
+A_421/2

test/Math/subscript/output

@@ -0,0 +1,32 @@
+A        
+ 2       
+
+A        
+ ⎛1⎞     
+ ⎜─⎟     
+ ⎝2⎠     
+      _  
+    ╲╱2  
+
+⎛A   ⎞   
+⎜ ⎛1⎞⎟   
+⎜ ⎜─⎟⎟   
+⎝ ⎝2⎠⎠   
+        _
+      ╲╱2
+
+A        
+ ⎛⎛1⎞   ⎞
+ ⎜⎜─⎟   ⎟
+ ⎜⎝2⎠   ⎟
+ ⎜     _⎟
+ ⎝   ╲╱2⎠
+
+       1 
+A    + ─ 
+ 421   2 
+
+A        
+ 421     
+────     
+  2