lower if

src/index.ts

@@ -10,14 +10,12 @@ import fs from "fs";
 import { exec } from "child_process";
 
 const input = `
-function printInt(a: Int) = (
-  let a = 0;
-  let b = 0;
-  let c = ();
-
-  a + b;
-
-  c
+function printInt(a: Int): Int = (
+  if true then (
+    0;
+    1;
+  );
+  0
 );
 
 function main() = ;

src/lower.ts

@@ -137,6 +137,8 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
         instrs.push({ kind: "local.set", imm: local });
 
         fcx.varLocations.push({ kind: "local", idx: local });
+      } else {
+        todo("complex locals");
       }
 
       break;
@@ -149,15 +151,10 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
       } else if (expr.exprs.length === 1) {
         lowerExpr(fcx, instrs, expr.exprs[0]);
       } else {
-        const typeIdx = internFuncType(fcx.cx, {
-          params: [],
-          returns: wasmTypeForBody(expr.ty!),
-        });
-
         const instr: wasm.Instr = {
           kind: "block",
           instrs: lowerExprBlockBody(fcx, expr),
-          type: { kind: "typeidx", idx: typeIdx },
+          type: blockTypeForBody(fcx.cx, expr.ty!),
         };
 
         instrs.push(instr);
@@ -306,8 +303,27 @@ function lowerExpr(fcx: FuncContext, instrs: wasm.Instr[], expr: Expr) {
     }
     case "call":
       todo("call");
-    case "if":
-      todo("ifs");
+    case "if": {
+      lowerExpr(fcx, instrs, expr.cond!);
+
+      const thenInstrs: wasm.Instr[] = [];
+      lowerExpr(fcx, thenInstrs, expr.then);
+
+      const elseInstrs: wasm.Instr[] = [];
+      // If there is no else, the type is (), so an empty instr array is correct.
+      if (expr.else) {
+        lowerExpr(fcx, elseInstrs, expr.else);
+      }
+
+      instrs.push({
+        kind: "if",
+        then: thenInstrs,
+        else: elseInstrs,
+        type: blockTypeForBody(fcx.cx, expr.ty!),
+      });
+
+      break;
+    }
   }
 }
 
@@ -467,6 +483,14 @@ function wasmTypeForBody(ty: Ty): wasm.ValType[] {
   }
 }
 
+function blockTypeForBody(cx: Context, ty: Ty): wasm.Blocktype {
+  const typeIdx = internFuncType(cx, {
+    params: [],
+    returns: wasmTypeForBody(ty),
+  });
+  return { kind: "typeidx", idx: typeIdx };
+}
+
 function todo(msg: string): never {
   throw new Error(`TODO: ${msg}`);
 }

src/typeck.ts

@@ -546,12 +546,13 @@ export function checkBody(
 
           infcx.assign(TY_BOOL, cond.ty!, cond.span);
 
-          let ty;
+          let ty: Ty;
           if (elsePart) {
             infcx.assign(then.ty!, elsePart.ty!, elsePart.span);
             ty = then.ty!;
           } else {
             infcx.assign(TY_UNIT, then.ty!, then.span);
+            ty = TY_UNIT;
           }
 
           return { ...expr, cond, then, else: elsePart, ty };