WIP: ternary operator

Author: rkalis

.cspell.json

@@ -8,6 +8,7 @@
         "algolia",
         "altstack",
         "antlr",
+        "assoc",
         "authchain",
         "anyhedge",
         "anyonecanpay",

packages/cashc/src/Errors.ts

@@ -9,6 +9,7 @@ import {
   FunctionCallNode,
   BinaryOpNode,
   UnaryOpNode,
+  TernaryNode,
   TimeOpNode,
   CastNode,
   AssignNode,
@@ -222,6 +223,19 @@ export class UnequalTypeError extends TypeError {
   }
 }
 
+export class TernaryBranchMismatchError extends TypeError {
+  constructor(
+    node: TernaryNode,
+  ) {
+    const consequent = node.consequent.type;
+    const alternative = node.alternative.type;
+    super(
+      node, consequent, alternative,
+      `Ternary branches have incompatible types '${consequent}' and '${alternative}'`,
+    );
+  }
+}
+
 export class UnsupportedTypeError extends TypeError {
   constructor(
     node: BinaryOpNode | UnaryOpNode | TimeOpNode | TupleIndexOpNode | SliceNode,

packages/cashc/src/ast/AST.ts

@@ -385,6 +385,20 @@ export class UnaryOpNode extends ExpressionNode {
   }
 }
 
+export class TernaryNode extends ExpressionNode {
+  constructor(
+    public condition: ExpressionNode,
+    public consequent: ExpressionNode,
+    public alternative: ExpressionNode,
+  ) {
+    super();
+  }
+
+  accept<T>(visitor: AstVisitor<T>): T {
+    return visitor.visitTernary(this);
+  }
+}
+
 export class NullaryOpNode extends ExpressionNode {
   constructor(
     public operator: NullaryOperator,

packages/cashc/src/ast/AstBuilder.ts

@@ -18,6 +18,7 @@ import {
   FunctionCallNode,
   UnaryOpNode,
   BinaryOpNode,
+  TernaryNode,
   BoolLiteralNode,
   IntLiteralNode,
   HexLiteralNode,
@@ -74,6 +75,7 @@ import type {
   InstantiationContext,
   NullaryOpContext,
   UnaryIntrospectionOpContext,
+  TernaryContext,
   ConsoleStatementContext,
   ConsoleParameterContext,
   StatementContext,
@@ -464,6 +466,15 @@ export default class AstBuilder
     return binaryOp;
   }
 
+  visitTernary(ctx: TernaryContext): TernaryNode {
+    const condition = this.visit(ctx._condition);
+    const consequent = this.visit(ctx._consequent);
+    const alternative = this.visit(ctx._alternative);
+    const ternary = new TernaryNode(condition, consequent, alternative);
+    ternary.location = Location.fromCtx(ctx);
+    return ternary;
+  }
+
   visitArray(ctx: ArrayContext): ArrayNode {
     const elements = ctx.expression_list().map((e) => this.visit(e));
     const array = new ArrayNode(elements);

packages/cashc/src/ast/AstTraversal.ts

@@ -13,6 +13,7 @@ import {
   FunctionCallNode,
   UnaryOpNode,
   BinaryOpNode,
+  TernaryNode,
   BoolLiteralNode,
   IntLiteralNode,
   HexLiteralNode,
@@ -172,6 +173,13 @@ export default class AstTraversal extends AstVisitor<Node> {
     return node;
   }
 
+  visitTernary(node: TernaryNode): Node {
+    node.condition = this.visit(node.condition);
+    node.consequent = this.visit(node.consequent);
+    node.alternative = this.visit(node.alternative);
+    return node;
+  }
+
   visitUnaryOp(node: UnaryOpNode): Node {
     node.expression = this.visit(node.expression);
     return node;

packages/cashc/src/ast/AstVisitor.ts

@@ -13,6 +13,7 @@ import {
   FunctionCallNode,
   UnaryOpNode,
   BinaryOpNode,
+  TernaryNode,
   BoolLiteralNode,
   IntLiteralNode,
   HexLiteralNode,
@@ -59,6 +60,7 @@ export default abstract class AstVisitor<T> {
   abstract visitSlice(node: SliceNode): T;
   abstract visitTupleIndexOp(node: TupleIndexOpNode): T;
   abstract visitBinaryOp(node: BinaryOpNode): T;
+  abstract visitTernary(node: TernaryNode): T;
   abstract visitUnaryOp(node: UnaryOpNode): T;
   abstract visitNullaryOp(node: NullaryOpNode): T;
   abstract visitArray(node: ArrayNode): T;

packages/cashc/src/generation/GenerateTargetTraversal.ts

@@ -36,6 +36,7 @@ import {
   FunctionCallNode,
   UnaryOpNode,
   BinaryOpNode,
+  TernaryNode,
   BoolLiteralNode,
   IntLiteralNode,
   HexLiteralNode,
@@ -806,6 +807,31 @@ export default class GenerateTargetTraversal extends AstTraversal {
     return node;
   }
 
+  // A ternary `condition ? consequent : alternative` compiles to OP_IF <consequent> OP_ELSE <alternative> OP_ENDIF.
+  // The condition is consumed by OP_IF; each branch leaves exactly one value, so the net effect mirrors any other
+  // expression: one operand consumed, one result produced. We bump scopeDepth (so variable reads inside the branches
+  // use OP_PICK rather than OP_ROLL, keeping the stack depth identical on both paths) and reset the symbolic stack
+  // before the alternative so both branches are tracked from the same starting point.
+  visitTernary(node: TernaryNode): Node {
+    node.condition = this.visit(node.condition);
+    this.popFromStack();
+
+    this.scopeDepth += 1;
+
+    this.emit(Op.OP_IF, { location: node.consequent.location, positionHint: PositionHint.START });
+    const stackCopy = [...this.stack];
+    node.consequent = this.visit(node.consequent);
+
+    this.emit(Op.OP_ELSE, { location: node.alternative.location, positionHint: PositionHint.START });
+    this.stack = [...stackCopy];
+    node.alternative = this.visit(node.alternative);
+
+    this.emit(Op.OP_ENDIF, { location: node.location, positionHint: PositionHint.END });
+    this.scopeDepth -= 1;
+
+    return node;
+  }
+
   visitNullaryOp(node: NullaryOpNode): Node {
     this.emit(compileNullaryOp(node.operator), { location: node.location, positionHint: PositionHint.START });
     this.pushToStack('(value)');

packages/cashc/src/grammar/CashScript.g4

@@ -186,6 +186,7 @@ expression
     | left=expression op='|' right=expression # BinaryOp
     | left=expression op='&&' right=expression # BinaryOp
     | left=expression op='||' right=expression # BinaryOp
+    | <assoc=right> condition=expression '?' consequent=expression ':' alternative=expression # Ternary
     | '[' (expression (',' expression)* ','?)? ']' # Array
     | NullaryOp # NullaryOp
     | Identifier # Identifier