feat: adds try/catch effects

3 files changed, 40 insertions, 3 deletions

diff --git a/examples/file.ts b/examples/file.ts
index d91b68a..fd5728b 100644
--- a/examples/file.ts
+++ b/examples/file.ts
@@ -1,9 +1,23 @@
 import { Bind, Kind1 } from '../stdlib/effect'
 import { PutStringLn } from '../stdlib/stdio'
 import { ReadFile } from '../stdlib/fs'
+import { Try } from '../stdlib/exception'
 
 interface PrintK extends Kind1<string> {
   return: PutStringLn<this['input']>
 }
 
-export type main = Bind<ReadFile<'./default.nix'>, PrintK>
+interface ConstK<Val> extends Kind1<unknown, Val> {
+  return: Val
+}
+
+export type main = [
+  Bind<ReadFile<'./default.nix'>, PrintK>,
+  Bind<
+    Try<
+      ReadFile<'./unicorn'>,
+      ConstK<"hello world">
+    >,
+    PrintK
+  >,
+]
diff --git a/src/eval.ts b/src/eval.ts
index c34e911..12997b1 100644
--- a/src/eval.ts
+++ b/src/eval.ts
@@ -4,6 +4,7 @@ import readline from 'readline'
 
 import { match } from './util'
 import { Ctx } from './types'
+import { assert } from 'console'
 
 const rl = readline.createInterface({
   input: process.stdin,
@@ -117,8 +118,25 @@ export const evaluateType = async (
     },
 
     Exit: async () => {
-      const exitCode = args[0] && ctx.getTypeValue(args[0])
-      process.exit(exitCode)
+      process.exit(args[0] && ctx.getTypeValue(args[0]))
+    },
+
+    Try: async () => {
+      const [effTyp, catchK] = args
+
+      try {
+        if (!effTyp) throw new Error('wow')
+        return await evaluateType(ctx, effTyp)
+      } catch(e) {
+        const error = JSON.stringify((e as any)?.message ?? e)
+        const catchResExpr = `(${ctx.typeToString(catchK)} & { input: ${error} })['return']`
+        const [resultKey, _] = ctx.createResult(catchResExpr)
+        return [resultKey]
+      }
+    },
+
+    Throw: async () => {
+      throw args[0] && ctx.getTypeValue(args[0])
     },
 
     ReadLine: async () => {
diff --git a/stdlib/exception.ts b/stdlib/exception.ts
new file mode 100644
index 0000000..731b3b0
--- /dev/null
+++ b/stdlib/exception.ts
@@ -0,0 +1,5 @@
+import { Effect, Kind1 } from "./effect";
+
+export interface Try<_E extends Effect, _Catch extends Kind1> extends Effect {}
+
+export interface Throw<_E> extends Effect {}