perf(lexer): generate if statement instead of switch

In itself, this won't make the lexer faster, but it is a precondition
for implementing subsequent optimization ideas listed in:

- #207

packages/codegen/src/ast.ts

@@ -17,21 +17,23 @@ type AssignmentStatement = {
 type BinaryExpression = {
   kind: 'BinaryExpression';
   lexpr: Expression;
-  operator:
-    | '!='
-    | '!=='
-    | '&&'
-    | '<'
-    | '<='
-    | '=='
-    | '==='
-    | '>'
-    | '>='
-    | '||'
-    | '+';
+  operator: BinaryOperator;
   rexpr: Expression;
 };
 
+type BinaryOperator =
+  | '!='
+  | '!=='
+  | '&&'
+  | '<'
+  | '<='
+  | '=='
+  | '==='
+  | '>'
+  | '>='
+  | '||'
+  | '+';
+
 type BooleanValue = {
   kind: 'BooleanValue';
   value: boolean;
@@ -55,7 +57,14 @@ type ClassDeclaration = {
   body: Array<MethodDefinition | PropertyDeclaration>;
 };
 
-type Consequent = {
+// Better AST might be
+// IfStatement
+//    Condition
+//    Consequent (Array<Statement>)
+//    Alternate (can be another IfStatement, for `else if`, or Array<Statement>,
+//    for `else`)
+// The name "Consequent" sucks.
+export type Consequent = {
   kind: 'Consequent';
   condition: Expression;
   block: Array<Statement>;
@@ -325,7 +334,11 @@ const ast = {
     }
   },
 
-  binop(lexpr: Expression, operator: '<', rexpr: Expression): BinaryExpression {
+  binop(
+    lexpr: Expression,
+    operator: BinaryOperator,
+    rexpr: Expression,
+  ): BinaryExpression {
     return {
       kind: 'BinaryExpression',
       lexpr,
@@ -382,6 +395,10 @@ const ast = {
     };
   },
 
+  equals(lexpr: Expression, rexpr: Expression): BinaryExpression {
+    return ast.binop(lexpr, '===', rexpr);
+  },
+
   expression(template: string): Expression {
     if (/^\d+$/.test(template)) {
       return ast.number(parseInt(template));

packages/codegen/src/index.ts

@@ -3,6 +3,7 @@ export {default as print} from './print';
 export {default as quote} from './quote';
 
 export type {
+  Consequent,
   Expression,
   IfStatement,
   Program,