parser

src/printer.ts

@@ -0,0 +1,96 @@
+import { Expr, FunctionDef, Item } from "./ast";
+
+export function printAst(ast: Item[]): string {
+  return ast.map(printItem).join("\n");
+}
+
+function printItem(item: Item): string {
+  switch (item.kind) {
+    case "function": {
+      return printFunction(item.node);
+    }
+  }
+}
+
+function printFunction(func: FunctionDef): string {
+  const args = func.args.map(({ name }) => name).join(", ");
+  return `function ${func.name}(${args}) = ${printExpr(func.body, 0)}`;
+}
+
+function printExpr(expr: Expr, indent: number): string {
+  switch (expr.kind) {
+    case "empty": {
+      return "";
+    }
+    case "let": {
+      return `let ${expr.name} = ${printExpr(expr.rhs, 1)} in${linebreak(
+        indent
+      )}`;
+    }
+    case "block": {
+      const exprs = expr.exprs.map((expr) => printExpr(expr, indent + 1));
+
+      if (exprs.length === 1) {
+        return `(${exprs[0]})`;
+      }
+      const shortExprs =
+        exprs.map((s) => s.length).reduce((a, b) => a + b, 0) < 40;
+      if (shortExprs) {
+        const alreadyHasTrailingSpace = expr.exprs[exprs.length - 1]?.kind === "empty";
+        const trailingSpace = alreadyHasTrailingSpace ? "" : " ";
+        return `( ${exprs.join("; ")}${trailingSpace})`;
+      } else {
+        const joiner = `;${linebreak(indent + 1)}`;
+        return (
+          `(${linebreak(indent + 1)}` +
+          `${exprs.join(joiner)}` +
+          `${linebreak(indent)})`
+        );
+      }
+    }
+    case "literal": {
+      switch (expr.value.kind) {
+        case "str": {
+          return `"${expr.value.value}"`;
+        }
+        case "int": {
+          return `${expr.value.value}`;
+        }
+      }
+    }
+    case "ident": {
+      return expr.value;
+    }
+    case "binary": {
+      return `${printExpr(expr.lhs, indent)} ${expr.binaryKind} ${printExpr(
+        expr.rhs,
+        indent
+      )}`;
+    }
+    case "unary": {
+      return `${expr.unaryKind}${printExpr(expr.rhs, indent)}`;
+    }
+    case "call": {
+      const args = expr.args.map((arg) => printExpr(arg, indent + 1));
+      const shortArgs =
+        args.map((s) => s.length).reduce((a, b) => a + b, 0) < 40;
+      if (shortArgs) {
+        return `${printExpr(expr.lhs, indent)}(${args.join(", ")})`;
+      } else {
+        return (
+          `${printExpr(expr.lhs, indent)}(${linebreak(indent + 1)}` +
+          `${args.join(linebreak(indent + 1))}` +
+          `${linebreak(indent)})`
+        );
+      }
+    }
+  }
+}
+
+function linebreak(indent: number): string {
+  return `\n${ind(indent)}`;
+}
+
+function ind(indent: number): string {
+  return "  ".repeat(indent * 2);
+}