Put + operator inbetween

source/elna/lexer.d

@@ -14,7 +14,7 @@ struct Token
     enum Type
     {
         number,
-        subroutine, // Operator.
+        operator,
         let,
         identifier,
         equals,
@@ -236,7 +236,7 @@ Array!Token lex(char[] buffer) @nogc
         }
         else if (source.front == '+') // Multi-character, random special characters.
         {
-            tokens.insertBack(Token(Token.Type.subroutine, source.position));
+            tokens.insertBack(Token(Token.Type.operator, source.position));
             source.popFront;
         }
         else if (source.front == '\n')

source/elna/parser.d

@@ -59,46 +59,22 @@ class Subroutine : Expression
     Expression lhs, rhs;
 }
 
-private Result!Expression parseExpression(ref Array!(Token).Range tokens) @nogc
-in (!tokens.empty, "Expected expression, got end of stream")
+private Result!Expression parseFactor(ref Array!Token.Range tokens) @nogc
+in (!tokens.empty, "Expected factor, got end of stream")
 {
-    if (tokens.front.ofType(Token.Type.number))
-    {
-        auto number = MmapPool.instance.make!Number;
-        number.value = tokens.front.value!(Token.Type.number);
-        tokens.popFront;
-        return Result!Expression(number);
-    }
-    else if (tokens.front.ofType(Token.Type.identifier))
+    if (tokens.front.ofType(Token.Type.identifier))
     {
         auto variable = MmapPool.instance.make!Variable;
         variable.identifier = tokens.front.value!(Token.Type.identifier);
         tokens.popFront;
         return Result!Expression(variable);
     }
-    else if (tokens.front.ofType(Token.Type.subroutine))
+    else if (tokens.front.ofType(Token.Type.number))
     {
-        auto subroutine = MmapPool.instance.make!Subroutine;
+        auto number = MmapPool.instance.make!Number;
+        number.value = tokens.front.value!(Token.Type.number);
         tokens.popFront;
-        auto expression = parseExpression(tokens);
-        if (expression.valid)
-        {
-            subroutine.lhs = expression.result;
-        }
-        else
-        {
-            return Result!Expression("Expected left-hand side to be an expression", tokens.front.position);
-        }
-        expression = parseExpression(tokens);
-        if (expression.valid)
-        {
-            subroutine.rhs = expression.result;
-        }
-        else
-        {
-            return Result!Expression("Expected left-hand side to be an expression", tokens.front.position);
-        }
-        return Result!Expression(subroutine);
+        return Result!Expression(number);
     }
     else if (tokens.front.ofType(Token.Type.leftParen))
     {
@@ -109,7 +85,38 @@ in (!tokens.empty, "Expected expression, got end of stream")
         tokens.popFront;
         return expression;
     }
-    return Result!Expression("Expected an expression", tokens.front.position);
+    return Result!Expression("Expected a factor", tokens.front.position);
+}
+
+private Result!Expression parseTerm(ref Array!(Token).Range tokens) @nogc
+{
+    return parseFactor(tokens);
+}
+
+private Result!Expression parseExpression(ref Array!(Token).Range tokens) @nogc
+in (!tokens.empty, "Expected expression, got end of stream")
+{
+    auto term = parseTerm(tokens);
+    if (!term.valid || tokens.empty || !tokens.front.ofType(Token.Type.operator))
+    {
+        return term;
+    }
+    tokens.popFront;
+
+    auto operator = MmapPool.instance.make!Subroutine;
+    auto expression = parseExpression(tokens);
+
+    if (expression.valid)
+    {
+        operator.lhs = term.result;
+        operator.rhs = expression.result;
+
+        return Result!Expression(operator);
+    }
+    else
+    {
+        return Result!Expression("Expected right-hand side to be an expression", tokens.front.position);
+    }
 }
 
 private Result!Definition parseDefinition(ref Array!Token.Range tokens) @nogc

tests/const_list.eln

@@ -1,3 +1,3 @@
 const a = 1, b = 2;
-! + a b
+! a + b
 .

tests/left_nested_sum.eln

@@ -1,2 +1,2 @@
-! + (+ 3 4) 1
+! (3 + 4) + 1
 .

tests/sum.eln

@@ -1,2 +1,2 @@
-! + 1 7
+! 1 + 7
 .

tests/sums.eln

@@ -1,2 +1,2 @@
-! + 1 (+ 3 4)
+! 1 + (3 + 4)
 .