4 files changed, 75 insertions, 26 deletions

diff --git a/utils/either.ts b/utils/either.ts
new file mode 100644
index 0000000..d21c796
--- /dev/null
+++ b/utils/either.ts
@@ -0,0 +1,25 @@
+export interface IEither<E, T> {
+  ok?: T;
+  err?: E;
+  mapBoth: <Ee, Tt>(
+    errBranch: (e: E) => Ee,
+    okBranch: (o: T) => Tt,
+  ) => IEither<Ee, Tt>;
+}
+
+export class Either<E, T> implements IEither<E, T> {
+  private constructor(readonly err?: E, readonly ok?: T) {}
+
+  public mapBoth<Ee, Tt>(errBranch: (e: E) => Ee, okBranch: (t: T) => Tt) {
+    if (this.err) return new Either<Ee, Tt>(errBranch(this.err));
+    return new Either<Ee, Tt>(undefined, okBranch(this.ok!));
+  }
+
+  static left<E, T>(e: E) {
+    return new Either<E, T>(e);
+  }
+
+  static right<E, T>(t: T) {
+    return new Either<E, T>(undefined, t);
+  }
+}
diff --git a/utils/mod.ts b/utils/mod.ts
index a8a0751..53ea173 100644
--- a/utils/mod.ts
+++ b/utils/mod.ts
@@ -1,4 +1,5 @@
 export * from "./trace.ts";
+export * from "./either.ts";
 export * from "./env.ts";
 export * from "./run.ts";
 export * from "./secret.ts";
diff --git a/utils/run.ts b/utils/run.ts
index 60ae1e6..06e7d9f 100644
--- a/utils/run.ts
+++ b/utils/run.ts
@@ -1,7 +1,10 @@
+import { Either } from "./mod.ts";
+
+export class ProcessError extends Error {}
 export const getStdout = async (
   cmd: string[] | string,
   options: Deno.CommandOptions = {},
-): Promise<string> => {
+): Promise<Either<ProcessError, string>> => {
   const [exec, ...args] = (typeof cmd === "string") ? cmd.split(" ") : cmd;
   const command = new Deno.Command(exec, {
     args,
@@ -10,12 +13,21 @@ export const getStdout = async (
     ...options,
   });
 
-  const { code, stdout, stderr } = await command.output();
-
-  const stdoutText = new TextDecoder().decode(stdout);
-  const stderrText = new TextDecoder().decode(stderr);
-
-  if (code !== 0) throw new Error(`command failed\n${stderrText}`);
+  try {
+    const { code, stdout, stderr } = await command.output();
+    const stdoutText = new TextDecoder().decode(stdout);
+    const stderrText = new TextDecoder().decode(stderr);
 
-  return stdoutText;
+    if (code !== 0) {
+      return Either.left<ProcessError, string>(
+        new ProcessError(`command failed\n${stderrText}`),
+      );
+    }
+    return Either.right<ProcessError, string>(stdoutText);
+  } catch (e) {
+    if (e instanceof Error) {
+      return Either.left<ProcessError, string>(e);
+    }
+    throw new Error("unknown error " + e);
+  }
 };
diff --git a/utils/trace.ts b/utils/trace.ts
index eb4ac2f..373f37e 100644
--- a/utils/trace.ts
+++ b/utils/trace.ts
@@ -25,12 +25,15 @@ export interface ITraceable<T, L extends ITraceableLogger<L>> {
     mapper: ITraceableMapper<T, L, ITraceableTuple<U>>,
   ) => ITraceable<U, L>;
   peek: (peek: ITraceableMapper<T, L, void>) => ITraceable<T, L>;
-  flatMap: <U>(mapper: ITraceableMapper<T, L, ITraceable<U, L>>) => ITraceable<U, L>;
-  flatMapAsync<U>(mapper: ITraceableMapper<T, L, Promise<ITraceable<U, L>>>): ITraceable<Promise<U>, L>;
+  flatMap: <U>(
+    mapper: ITraceableMapper<T, L, ITraceable<U, L>>,
+  ) => ITraceable<U, L>;
+  flatMapAsync<U>(
+    mapper: ITraceableMapper<T, L, Promise<ITraceable<U, L>>>,
+  ): ITraceable<Promise<U>, L>;
 }
 
-export class TraceableLogger
-  implements ITraceableLogger<TraceableLogger> {
+export class TraceableLogger implements ITraceableLogger<TraceableLogger> {
   private readonly logger: Logger = console;
   constructor(
     private readonly traces = [() => `[${new Date().toISOString()}]`],
@@ -62,23 +65,30 @@ export class TraceableLogger
   }
 }
 
-export class TraceableImpl<
+class TraceableImpl<
   T,
   L extends ITraceableLogger<L>,
 > implements ITraceable<T, L> {
-  private constructor(readonly item: T, readonly logger: L) {}
+  protected constructor(readonly item: T, readonly logger: L) {}
 
   public map<U>(mapper: ITraceableMapper<T, L, U>) {
     const result = mapper(this);
     return new TraceableImpl(result, this.logger);
   }
 
-  public flatMap<U>(mapper: ITraceableMapper<T, L, ITraceable<U, L>>): ITraceable<U, L> {
+  public flatMap<U>(
+    mapper: ITraceableMapper<T, L, ITraceable<U, L>>,
+  ): ITraceable<U, L> {
     return mapper(this);
   }
 
-  public flatMapAsync<U>(mapper: ITraceableMapper<T, L, Promise<ITraceable<U, L>>>): ITraceable<Promise<U>, L> {
-    return new TraceableImpl(mapper(this).then(({ item }) => item), this.logger);
+  public flatMapAsync<U>(
+    mapper: ITraceableMapper<T, L, Promise<ITraceable<U, L>>>,
+  ): ITraceable<Promise<U>, L> {
+    return new TraceableImpl(
+      mapper(this).then(({ item }) => item),
+      this.logger,
+    );
   }
 
   public peek(peek: ITraceableMapper<T, L, void>) {
@@ -95,20 +105,21 @@ export class TraceableImpl<
     mapper: ITraceableMapper<T, L, U>,
   ): ITraceableMapper<Promise<T>, L, Promise<U>> {
     return (traceablePromise) =>
-        traceablePromise.flatMapAsync(async (t) => {
-          const item = await t.item;
-          return t.map(() => item).map(mapper);
-        }).item;
+      traceablePromise.flatMapAsync(async (t) => {
+        const item = await t.item;
+        return t.map(() => item).map(mapper);
+      }).item;
   }
+}
 
-  static withClassTrace<C extends Object, T, L extends ITraceableLogger<L>>(c: C): ITraceableMapper<T, L, ITraceableTuple<T>> {
+export class Traceable<T> extends TraceableImpl<T, TraceableLogger> {
+  static withClassTrace<C extends object, T>(
+    c: C,
+  ): ITraceableMapper<T, TraceableLogger, ITraceableTuple<T>> {
     return (t) => [t.item, () => c.constructor.name];
   }
 
   static from<T>(t: T) {
-    return new TraceableImpl(t, new TraceableLogger());
+    return new Traceable(t, new TraceableLogger());
   }
 }
-
-export interface Traceable<T, L extends ITraceableLogger<L> = TraceableLogger> extends ITraceable<T, L> {
-}