implement field accesses

src/ast.ts

@@ -120,6 +120,16 @@ export type ExprCall = {
   args: Expr[];
 };
 
+export type ExprFieldAccess = {
+  kind: "fieldAccess";
+  lhs: Expr;
+  field: {
+    value: string | number;
+    span: Span;
+    fieldIdx?: number;
+  };
+};
+
 export type ExprIf = {
   kind: "if";
   cond: Expr;
@@ -161,6 +171,7 @@ export type ExprKind =
   | ExprBinary
   | ExprUnary
   | ExprCall
+  | ExprFieldAccess
   | ExprIf
   | ExprLoop
   | ExprBreak
@@ -546,6 +557,13 @@ export function superFoldExpr(expr: Expr, folder: Folder): Expr {
         args: expr.args.map((expr) => folder.expr(expr)),
       };
     }
+    case "fieldAccess": {
+      return {
+        ...expr,
+        kind: "fieldAccess",
+        lhs: folder.expr(expr.lhs),
+      };
+    }
     case "if": {
       return {
         ...expr,

src/index.ts

@@ -11,71 +11,12 @@ import { exec } from "child_process";
 
 const INPUT = `
 function main() = (
-  prIntln(0);
-  prIntln(1);
-  prIntln(9);
-  prIntln(2352353);
-  prIntln(100);
+  printTuples(("hello, ", "world\\n"));
 );
 
-function prIntln(x: Int) = (
-  prInt(x);
-  print("\n");
-);
-
-function stringForDigit(x: Int): String = 
-  if x == 0 then "0"
-  else if x == 1 then "1"
-  else if x == 2 then "2"
-  else if x == 3 then "3"
-  else if x == 4 then "4"
-  else if x == 5 then "5"
-  else if x == 6 then "6"
-  else if x == 7 then "7"
-  else if x == 8 then "8"
-  else if x == 9 then "9"
-  else trap();
-
-function log10(x: Int): Int = (
-  let i = 0;
-  loop (
-    if x < 10 then break;
-    i = i + 1;
-    x = x / 10;
-  );
-  i
-);
-
-function pow(base: Int, exp: Int): Int = (
-  let acc = 1;
-  loop (
-    if exp == 0 then break;
-    acc = acc * base;
-    exp = exp - 1;
-  );
-  acc
-);
-
-function prInt(x: Int) = (
-  let mag = log10(x);
-
-  loop (
-    if mag == 0 then break;
-    let base = pow(10, mag);
-
-    let digit = x / base;
-    print(stringForDigit(digit));
-
-    x = x % base;
-    mag = mag - 1;
-  );
-
-  print(stringForDigit(x % 10));
-);
-
-function println(s: String) = (
-  print(s);
-  print("\n");
+function printTuples(a: (String, String)) = (
+  print(a.0);
+  print(a.1);
 );
 `;
 

src/lexer.ts

@@ -18,6 +18,7 @@ export type DatalessToken =
   | "]"
   | ";"
   | ":"
+  | "."
   | ","
   | "="
   | "+"
@@ -70,6 +71,7 @@ const SINGLE_PUNCT: string[] = [
   "]",
   ";",
   ":",
+  ".",
   ",",
   "+",
   "-",
@@ -245,7 +247,7 @@ export function tokenize(input: string): Token[] {
           } else if (isWhitespace(next)) {
             // ignore
           } else {
-            throw new CompilerError(`Invalid character: \`${next}\``, span);
+            throw new CompilerError(`invalid character: \`${next}\``, span);
           }
         }
       }

src/lower.ts

@@ -9,6 +9,7 @@ import {
   Resolution,
   Ty,
   TyFn,
+  TyTuple,
   varUnreachable,
 } from "./ast";
 import { encodeUtf8, unwrap } from "./utils";
@@ -558,6 +559,68 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
       instrs.push(callInstr);
       break;
     }
+    case "fieldAccess": {
+      // We could just naively always evaluate the LHS normally, but that's kinda
+      // stupid as it would cause way too much code for `let a = (0, 0, 0); a.0`
+      // as that operation would first load the entire tuple onto the stack!
+      // Therefore, we are a little clever be peeking into the LHS and doing
+      // something smarter if it's another field access or ident (in the future,
+      // we should be able to generalize this to all "places"/"lvalues").
+
+      // TODO: Actually do this instead of being naive.
+
+      const isPlace = (expr: Expr) =>
+        expr.kind === "ident" || expr.kind === "fieldAccess";
+
+      function project() {}
+
+      lowerExpr(fcx, instrs, expr.lhs);
+
+      switch (expr.lhs.ty!.kind) {
+        case "tuple": {
+          // Tuples have a by-value ABI, so we can simply index.
+          const lhsSize = argRetAbi(expr.lhs.ty!).length;
+          const resultAbi = argRetAbi(expr.ty!);
+          const resultSize = resultAbi.length;
+          const wasmIdx = wasmTypeIdxForTupleField(
+            expr.lhs.ty!,
+            expr.field.fieldIdx!
+          );
+
+          // lhsSize=5, resultSize=2, wasmIdx=2
+          // I I Y Y I
+          // drop, 2xlocal.set, drop, drop, 2xlocal.get
+
+          // TODO: Establish some way of having reusable "scratch locals".
+          const localIdx = fcx.wasm.locals.length + fcx.wasmType.params.length;
+          fcx.wasm.locals.push(...resultAbi);
+
+          Array(lhsSize - wasmIdx - resultSize)
+            .fill(0)
+            .forEach(() => instrs.push({ kind: "drop" }));
+
+          if (expr.field.fieldIdx! > 0) {
+            // Keep the result in scratch space.
+            storeVariable(instrs, { localIdx, types: resultAbi });
+
+            Array(wasmIdx)
+              .fill(0)
+              .forEach(() => instrs.push({ kind: "drop" }));
+
+            loadVariable(instrs, { localIdx, types: resultAbi });
+          }
+
+          break;
+        }
+        case "struct": {
+          todo("struct field accesses");
+        }
+        default:
+          throw new Error("invalid field access lhs");
+      }
+
+      break;
+    }
     case "if": {
       lowerExpr(fcx, instrs, expr.cond!);
 
@@ -690,32 +753,32 @@ function storeVariable(instrs: wasm.Instr[], loc: VarLocation) {
   });
 }
 
-function computeAbi(ty: TyFn): FnAbi {
-  function argRetAbi(param: Ty): ArgRetAbi {
-    switch (param.kind) {
-      case "string":
-        return STRING_ABI;
-      case "fn":
-        todo("fn abi");
-      case "int":
-        return ["i64"];
-      case "i32":
-        return ["i32"];
-      case "bool":
-        return ["i32"];
-      case "list":
-        todo("list abi");
-      case "tuple":
-        return param.elems.flatMap(argRetAbi);
-      case "struct":
-        todo("struct ABI");
-      case "never":
-        return [];
-      case "var":
-        varUnreachable();
-    }
+function argRetAbi(param: Ty): ArgRetAbi {
+  switch (param.kind) {
+    case "string":
+      return STRING_ABI;
+    case "fn":
+      todo("fn abi");
+    case "int":
+      return ["i64"];
+    case "i32":
+      return ["i32"];
+    case "bool":
+      return ["i32"];
+    case "list":
+      todo("list abi");
+    case "tuple":
+      return param.elems.flatMap(argRetAbi);
+    case "struct":
+      todo("struct ABI");
+    case "never":
+      return [];
+    case "var":
+      varUnreachable();
   }
+}
 
+function computeAbi(ty: TyFn): FnAbi {
   const params = ty.params.map(argRetAbi);
   const ret = argRetAbi(ty.returnTy);
 
@@ -773,6 +836,14 @@ function blockTypeForBody(cx: Context, ty: Ty): wasm.Blocktype {
   return { kind: "typeidx", idx: typeIdx };
 }
 
+function wasmTypeIdxForTupleField(ty: TyTuple, idx: number): number {
+  // Tuples are all flattened by value, so we just count the values in
+  // the flattened representation.
+  const layout = ty.elems.map(argRetAbi);
+  const head = layout.slice(0, idx);
+  return head.reduce((a, b) => a + b.length, 0);
+}
+
 function todo(msg: string): never {
   throw new Error(`TODO: ${msg}`);
 }

src/parser.ts

@@ -188,7 +188,7 @@ function parseExpr(t: Token[]): [Token[], Expr] {
 
   UNARY = { "!" | "-" } CALL
 
-  CALL = ATOM { "(" EXPR_LIST ")" }
+  CALL = ATOM { ( "(" EXPR_LIST ")" ) | ( "." ( IDENT | NUMBER ) ) }
 
   ATOM = "(" { EXPR ";" | "," } EXPR ")" | IDENT { STRUCT_INIT } | LITERAL | EMPTY | LET | IF | LOOP | BREAK
   EMPTY =
@@ -271,14 +271,34 @@ function parseExprCall(t: Token[]): [Token[], Expr] {
   let lhs: Expr;
   [t, lhs] = parseExprAtom(t);
 
-  while (next(t)[1].kind === "(") {
-    let popen;
-    [t, popen] = next(t);
+  while (next(t)[1].kind === "(" || next(t)[1].kind === ".") {
+    let tok;
+    [t, tok] = next(t);
 
-    let args;
-    [t, args] = parseCommaSeparatedList(t, ")", parseExpr);
+    if (tok.kind === "(") {
+      let args;
+      [t, args] = parseCommaSeparatedList(t, ")", parseExpr);
 
-    lhs = { kind: "call", span: popen.span, lhs, args };
+      lhs = { kind: "call", span: tok.span, lhs, args };
+    } else if (tok.kind === ".") {
+      let access;
+      [t, access] = next(t);
+      let value;
+      if (access.kind === "identifier") {
+        value = access.ident;
+      } else if (access.kind === "lit_int") {
+        value = access.value;
+      } else {
+        unexpectedToken(access, "identifier or integer");
+      }
+
+      lhs = {
+        kind: "fieldAccess",
+        lhs,
+        field: { span: access.span, value },
+        span: spanMerge(lhs.span, access.span),
+      };
+    }
   }
 
   return [t, lhs];
@@ -565,7 +585,10 @@ function expectNext<T extends BaseToken>(
   let tok;
   [t, tok] = next(t);
   if (tok.kind !== kind) {
-    throw new CompilerError(`expected \`${kind}\`, found \`${tok.kind}\``, tok.span);
+    throw new CompilerError(
+      `expected \`${kind}\`, found \`${tok.kind}\``,
+      tok.span
+    );
   }
   return [t, tok as unknown as T & Token];
 }

src/printer.ts

@@ -140,6 +140,9 @@ function printExpr(expr: Expr, indent: number): string {
         );
       }
     }
+    case "fieldAccess": {
+      return `${printExpr(expr.lhs, indent)}.${expr.field.value}`;
+    }
     case "if": {
       const elsePart = expr.else
         ? ` else ${printExpr(expr.else, indent + 1)}`

src/typeck.ts

@@ -677,6 +677,76 @@ export function checkBody(
 
           return { ...expr, lhs, args, ty: lhsTy.returnTy };
         }
+        case "fieldAccess": {
+          const lhs = this.expr(expr.lhs);
+          lhs.ty = infcx.resolveIfPossible(lhs.ty!);
+
+          const { field } = expr;
+          let ty: Ty;
+          let fieldIdx: number;
+          switch (lhs.ty.kind) {
+            case "tuple": {
+              const { elems } = lhs.ty;
+              if (typeof field.value === "number") {
+                if (elems.length > field.value) {
+                  ty = elems[field.value];
+                  fieldIdx = field.value;
+                } else {
+                  throw new CompilerError(
+                    `tuple with ${elems.length} elements cannot be indexed with ${field.value}`,
+                    field.span
+                  );
+                }
+              } else {
+                throw new CompilerError(
+                  "tuple fields must be accessed with numbers",
+                  field.span
+                );
+              }
+              break;
+            }
+            case "struct": {
+              if (typeof field.value === "string") {
+                const idx = lhs.ty.fields.findIndex(
+                  ([name]) => name === field.value
+                );
+                if (idx === -1) {
+                  throw new CompilerError(
+                    `field \`${field.value}\` does not exist on ${printTy(
+                      lhs.ty
+                    )}`,
+                    field.span
+                  );
+                }
+
+                ty = lhs.ty.fields[idx][1];
+                fieldIdx = idx;
+              } else {
+                throw new CompilerError(
+                  "struct fields must be accessed with their name",
+                  field.span
+                );
+              }
+              break;
+            }
+            default: {
+              throw new CompilerError(
+                "only tuples and structs have fields",
+                expr.span
+              );
+            }
+          }
+
+          return {
+            ...expr,
+            lhs,
+            field: {
+              ...expr.field,
+              fieldIdx,
+            },
+            ty,
+          };
+        }
         case "if": {
           const cond = this.expr(expr.cond);
           const then = this.expr(expr.then);