diff --git a/compiler/ast.ts b/compiler/ast.ts
index 7119da5..c9d81f0 100644
--- a/compiler/ast.ts
+++ b/compiler/ast.ts
@@ -31,6 +31,7 @@ export type StmtKind =
         vtype?: VType;
     }
     | { type: "let"; param: Param; value: Expr }
+    | { type: "type_alias"; param: Param }
     | { type: "assign"; assignType: AssignType; subject: Expr; value: Expr }
     | { type: "expr"; expr: Expr };
 
@@ -124,6 +125,7 @@ export type Sym = {
 export type SymKind =
     | { type: "let"; stmt: Stmt; param: Param }
     | { type: "let_static"; stmt: Stmt; param: Param }
+    | { type: "type_alias"; stmt: Stmt; param: Param }
     | { type: "fn"; stmt: Stmt }
     | { type: "fn_param"; param: Param }
     | { type: "closure"; inner: Sym }
diff --git a/compiler/ast_visitor.ts b/compiler/ast_visitor.ts
index 62eb19b..ba6c8ac 100644
--- a/compiler/ast_visitor.ts
+++ b/compiler/ast_visitor.ts
@@ -13,6 +13,7 @@ export interface AstVisitor<Args extends unknown[] = []> {
     visitReturnStmt?(stmt: Stmt, ...args: Args): VisitRes;
     visitFnStmt?(stmt: Stmt, ...args: Args): VisitRes;
     visitLetStmt?(stmt: Stmt, ...args: Args): VisitRes;
+    visitTypeAliasStmt?(stmt: Stmt, ...args: Args): VisitRes;
     visitAssignStmt?(stmt: Stmt, ...args: Args): VisitRes;
     visitExprStmt?(stmt: Stmt, ...args: Args): VisitRes;
     visitExpr?(expr: Expr, ...args: Args): VisitRes;
@@ -106,6 +107,10 @@ export function visitStmt<Args extends unknown[] = []>(
             visitParam(stmt.kind.param, v, ...args);
             visitExpr(stmt.kind.value, v, ...args);
             break;
+        case "type_alias":
+            if (v.visitTypeAliasStmt?.(stmt, ...args) == "stop") return;
+            visitParam(stmt.kind.param, v, ...args);
+            break;
         case "assign":
             if (v.visitAssignStmt?.(stmt, ...args) == "stop") return;
             visitExpr(stmt.kind.subject, v, ...args);
diff --git a/compiler/checker.ts b/compiler/checker.ts
index 7a42f4b..88b1c10 100644
--- a/compiler/checker.ts
+++ b/compiler/checker.ts
@@ -20,48 +20,56 @@ export class Checker {
     public constructor(private reporter: Reporter) {}
 
     public check(stmts: Stmt[]) {
-        this.checkFnHeaders(stmts);
+        this.scout(stmts);
         for (const stmt of stmts) {
             this.checkStmt(stmt);
         }
     }
 
-    private checkFnHeaders(stmts: Stmt[]) {
+    private scout(stmts: Stmt[]) {
         for (const stmt of stmts) {
-            if (stmt.kind.type !== "fn") {
-                continue;
-            }
-            let genericParams: VTypeGenericParam[] | undefined;
-            if (stmt.kind.genericParams !== undefined) {
-                genericParams = [];
-                for (const etypeParam of stmt.kind.genericParams) {
-                    const id = genericParams.length;
-                    const globalId = etypeParam.id;
-                    const param = { id, ident: etypeParam.ident };
-                    genericParams.push(param);
-                    this.globalIdToGenericParamMap.set(globalId, param);
+            if (stmt.kind.type === "fn") {
+                let genericParams: VTypeGenericParam[] | undefined;
+                if (stmt.kind.genericParams !== undefined) {
+                    genericParams = [];
+                    for (const etypeParam of stmt.kind.genericParams) {
+                        const id = genericParams.length;
+                        const globalId = etypeParam.id;
+                        const param = { id, ident: etypeParam.ident };
+                        genericParams.push(param);
+                        this.globalIdToGenericParamMap.set(globalId, param);
+                    }
                 }
-            }
-            const params: VTypeParam[] = [];
-            for (const param of stmt.kind.params) {
-                if (param.etype === undefined) {
-                    this.report("parameter types must be defined", param.pos);
-                    stmt.kind.vtype = { type: "error" };
+                const params: VTypeParam[] = [];
+                for (const param of stmt.kind.params) {
+                    if (param.etype === undefined) {
+                        this.report(
+                            "parameter types must be defined",
+                            param.pos,
+                        );
+                        stmt.kind.vtype = { type: "error" };
+                    }
+                    const vtype = this.checkEType(param.etype!);
+                    param.vtype = vtype;
+                    params.push({ ident: param.ident, vtype });
                 }
-                const vtype = this.checkEType(param.etype!);
-                param.vtype = vtype;
-                params.push({ ident: param.ident, vtype });
+                const returnType: VType = stmt.kind.returnType
+                    ? this.checkEType(stmt.kind.returnType)
+                    : { type: "null" };
+                stmt.kind.vtype = {
+                    type: "fn",
+                    genericParams,
+                    params,
+                    returnType,
+                    stmtId: stmt.id,
+                };
+            } else if (stmt.kind.type === "type_alias") {
+                if (!stmt.kind.param.etype) {
+                    this.report("no type specified", stmt.pos);
+                    return;
+                }
+                stmt.kind.param.vtype = this.checkEType(stmt.kind.param.etype);
             }
-            const returnType: VType = stmt.kind.returnType
-                ? this.checkEType(stmt.kind.returnType)
-                : { type: "null" };
-            stmt.kind.vtype = {
-                type: "fn",
-                genericParams,
-                params,
-                returnType,
-                stmtId: stmt.id,
-            };
         }
     }
 
@@ -82,6 +90,8 @@ export class Checker {
                 return this.checkFnStmt(stmt);
             case "let":
                 return this.checkLetStmt(stmt);
+            case "type_alias":
+                return this.checkTypeAliasStmt(stmt);
             case "assign":
                 return this.checkAssignStmt(stmt);
             case "expr":
@@ -94,7 +104,7 @@ export class Checker {
             throw new Error();
         }
         const { ast } = stmt.kind.mod;
-        this.checkFnHeaders(ast);
+        this.scout(ast);
         for (const stmt of ast) {
             this.checkStmt(stmt);
         }
@@ -146,8 +156,8 @@ export class Checker {
         if (!vtypesEqual(exprType, returnType)) {
             this.report(
                 `incompatible return type` +
-                    `, got ${exprType}` +
-                    `, expected ${returnType}`,
+                    `, expected ${vtypeToString(returnType)}` +
+                    `, got ${vtypeToString(exprType)}`,
                 pos,
             );
         }
@@ -210,6 +220,18 @@ export class Checker {
         stmt.kind.param.vtype = value;
     }
 
+    public checkTypeAliasStmt(stmt: Stmt) {
+        if (stmt.kind.type !== "type_alias") {
+            throw new Error();
+        }
+        const pos = stmt.pos;
+        if (!stmt.kind.param.etype) {
+            this.report("no type specified", pos);
+            return;
+        }
+        stmt.kind.param.vtype = this.checkEType(stmt.kind.param.etype);
+    }
+
     public checkAssignStmt(stmt: Stmt) {
         if (stmt.kind.type !== "assign") {
             throw new Error();
@@ -373,6 +395,8 @@ export class Checker {
         switch (sym.type) {
             case "let":
                 return sym.param.vtype!;
+            case "type_alias":
+                return sym.param.vtype!;
             case "fn": {
                 const fnStmt = sym.stmt!;
                 if (fnStmt.kind.type !== "fn") {
@@ -923,7 +947,7 @@ export class Checker {
         if (expr.kind.type !== "block") {
             throw new Error();
         }
-        this.checkFnHeaders(expr.kind.stmts);
+        this.scout(expr.kind.stmts);
         for (const stmt of expr.kind.stmts) {
             this.checkStmt(stmt);
         }
@@ -949,6 +973,9 @@ export class Checker {
             return { type: "error" };
         }
         if (etype.kind.type === "sym") {
+            if (etype.kind.sym.type === "type_alias") {
+                return etype.kind.sym.param.vtype!;
+            }
             if (etype.kind.sym.type === "generic") {
                 const { id: globalId, ident } = etype.kind.sym.genericParam;
                 if (!this.globalIdToGenericParamMap.has(globalId)) {
diff --git a/compiler/desugar/struct_literal.ts b/compiler/desugar/struct_literal.ts
index 93405ad..0931f0d 100644
--- a/compiler/desugar/struct_literal.ts
+++ b/compiler/desugar/struct_literal.ts
@@ -8,7 +8,6 @@ import {
 } from "../ast.ts";
 import {
     AstVisitor,
-    visitExpr,
     visitField,
     VisitRes,
     visitStmts,
@@ -46,10 +45,6 @@ export class StructLiteralDesugarer implements AstVisitor {
                 ident,
             });
 
-        // Yes, I know this isn't a deep clone,
-        // but I don't really need it to be.
-        const oldExpr = { ...expr };
-
         const fields = expr.kind.fields;
 
         expr.kind = {
@@ -67,7 +62,10 @@ export class StructLiteralDesugarer implements AstVisitor {
                             type: "etype_args",
                             subject: std("struct_new"),
                             etypeArgs: [
-                                EType({ type: "type_of", expr: oldExpr }),
+                                EType({
+                                    type: "type_of",
+                                    expr: Expr({ ...expr.kind }),
+                                }),
                             ],
                         }),
                         args: [],
diff --git a/compiler/lexer.ts b/compiler/lexer.ts
index b7f34f1..a962341 100644
--- a/compiler/lexer.ts
+++ b/compiler/lexer.ts
@@ -50,6 +50,7 @@ export class Lexer {
                 "mod",
                 "pub",
                 "use",
+                "type_alias",
             ];
             if (keywords.includes(value)) {
                 return this.token(value, pos);
diff --git a/compiler/parser.ts b/compiler/parser.ts
index d854faa..03f6fbd 100644
--- a/compiler/parser.ts
+++ b/compiler/parser.ts
@@ -49,7 +49,7 @@ export class Parser {
         ) {
             return this.parseItemStmt();
         } else if (
-            ["let", "return", "break"].some((tt) => this.test(tt))
+            ["let", "type_alias", "return", "break"].some((tt) => this.test(tt))
         ) {
             const expr = this.parseSingleLineBlockStmt();
             this.eatSemicolon();
@@ -92,6 +92,9 @@ export class Parser {
         if (this.test("let")) {
             return this.parseLet();
         }
+        if (this.test("type_alias")) {
+            return this.parseTypeAlias();
+        }
         if (this.test("return")) {
             return this.parseReturn();
         }
@@ -129,7 +132,8 @@ export class Parser {
             ) {
                 stmts.push(this.parseItemStmt());
             } else if (
-                ["let", "return", "break"].some((tt) => this.test(tt))
+                ["let", "type_alias", "return", "break"]
+                    .some((tt) => this.test(tt))
             ) {
                 stmts.push(this.parseSingleLineBlockStmt());
                 this.eatSemicolon();
@@ -413,6 +417,17 @@ export class Parser {
         return this.stmt({ type: "let", param, value }, pos);
     }
 
+    private parseTypeAlias(): Stmt {
+        const pos = this.pos();
+        this.step();
+        const paramResult = this.parseParam();
+        if (!paramResult.ok) {
+            return this.stmt({ type: "error" }, pos);
+        }
+        const param = paramResult.value;
+        return this.stmt({ type: "type_alias", param }, pos);
+    }
+
     private parseAssign(): Stmt {
         const pos = this.pos();
         const subject = this.parseExpr();
diff --git a/compiler/resolver.ts b/compiler/resolver.ts
index 2d06de4..c811b28 100644
--- a/compiler/resolver.ts
+++ b/compiler/resolver.ts
@@ -24,18 +24,49 @@ export class Resolver implements AstVisitor<[Syms]> {
 
     public resolve(stmts: Stmt[]): VisitRes {
         const syms = new EntryModSyms();
-        this.scoutFnStmts(stmts, syms);
+        this.scout(stmts, syms);
         visitStmts(stmts, this, syms);
         return "stop";
     }
 
+    private scout(stmts: Stmt[], syms: Syms) {
+        for (const stmt of stmts) {
+            if (stmt.kind.type === "fn") {
+                if (syms.definedLocally(stmt.kind.ident)) {
+                    this.reportAlreadyDefined(stmt.kind.ident, stmt.pos, syms);
+                    return;
+                }
+                const ident = stmt.kind.ident;
+                syms.define(ident, {
+                    ident: stmt.kind.ident,
+                    type: "fn",
+                    pos: stmt.pos,
+                    stmt,
+                });
+            } else if (stmt.kind.type === "type_alias") {
+                const ident = stmt.kind.param.ident;
+                if (syms.definedLocally(ident)) {
+                    this.reportAlreadyDefined(ident, stmt.pos, syms);
+                    return;
+                }
+                syms.define(ident, {
+                    ident,
+                    type: "type_alias",
+                    pos: stmt.kind.param.pos,
+                    stmt,
+                    param: stmt.kind.param,
+                });
+            }
+        }
+    }
+
     visitModStmt(stmt: Stmt, syms: Syms): VisitRes {
         if (stmt.kind.type !== "mod") {
             throw new Error("expected let statement");
         }
         const modSyms = new ModSyms(syms);
         const { mod, ident } = stmt.kind;
-        this.scoutFnStmts(mod.ast, modSyms);
+        this.scout(mod.ast, modSyms);
         visitStmts(mod.ast, this, modSyms);
 
         if (syms.definedLocally(ident)) {
@@ -72,23 +103,11 @@ export class Resolver implements AstVisitor<[Syms]> {
         return "stop";
     }
 
-    private scoutFnStmts(stmts: Stmt[], syms: Syms) {
-        for (const stmt of stmts) {
-            if (stmt.kind.type !== "fn") {
-                continue;
-            }
-            if (syms.definedLocally(stmt.kind.ident)) {
-                this.reportAlreadyDefined(stmt.kind.ident, stmt.pos, syms);
-                return;
-            }
-            const ident = stmt.kind.ident;
-            syms.define(ident, {
-                ident: stmt.kind.ident,
-                type: "fn",
-                pos: stmt.pos,
-                stmt,
-            });
+    visitTypeAliasStmt(stmt: Stmt, syms: Syms): VisitRes {
+        if (stmt.kind.type !== "type_alias") {
+            throw new Error("expected type_alias statement");
         }
+        // nothing to do here
     }
 
     visitFnStmt(stmt: Stmt, syms: Syms): VisitRes {
@@ -186,7 +205,7 @@ export class Resolver implements AstVisitor<[Syms]> {
             throw new Error();
         }
         const childSyms = new LeafSyms(syms);
-        this.scoutFnStmts(expr.kind.stmts, childSyms);
+        this.scout(expr.kind.stmts, childSyms);
         visitStmts(expr.kind.stmts, this, childSyms);
         if (expr.kind.expr) {
             visitExpr(expr.kind.expr, this, childSyms);
diff --git a/runtime/alloc.hpp b/runtime/alloc.hpp
index 21c4f96..05c34da 100644
--- a/runtime/alloc.hpp
+++ b/runtime/alloc.hpp
@@ -205,7 +205,7 @@ private:
         }
     }
 
-    size_t max_size = 8;
+    size_t max_size = 512;
 
     std::vector<AllocItem> heap_1;
     std::vector<AllocItem> heap_2;
diff --git a/std/lib.slg b/std/lib.slg
index b5c8d79..3c85937 100644
--- a/std/lib.slg
+++ b/std/lib.slg
@@ -54,6 +54,8 @@ pub fn itos(number: int) -> string {}
 #[builtin(StringToInt)]
 pub fn stoi(str: string) -> int {}
 
+pub fn ctos(ch: int) -> string { string_push_char("", ch) }
+
 pub fn stdin() -> int { 0 }
 pub fn stdout() -> int { 1 }
 pub fn stderr() -> int { 2 }
@@ -81,7 +83,7 @@ pub fn read_text_file(filename: string) -> string {
 }
 
 pub fn input(prompt: string) -> string {
-    print("> ");
+    print(prompt);
     file_flush(stdout());
     file_read_line(stdin())
 }