Add some example programs

Author: mkantor

README.md

@@ -12,6 +12,8 @@ npm run build
 echo '{@runtime context => :context.program.start_time}' | ./please --output-format=json
 ```
 
+There are more example programs in [`./examples`](./examples).
+
 ## What This Repository Is
 
 **This implementation of Please is a proof of concept**. There are bugs and

examples/fibonacci.plz

@@ -0,0 +1,24 @@
+{
+  fibonacci: n => {
+    @if :integer.less_than(2)(:n)
+    then: :n
+    else: :integer.add(
+      :fibonacci(:integer.subtract(2)(:n))
+    )(
+      :fibonacci(:integer.subtract(1)(:n))
+    )
+  }
+
+  input: { @runtime context => :context.arguments.lookup(input) }
+
+  output: :apply(:input)(
+    :match({
+      none: _ => "missing input argument"
+      some: input => {
+        @if :natural_number.is(:input)
+        then: :fibonacci(:input)
+        else: "input must be a natural number"
+      }
+    })
+  )
+}.output

examples/kitchen-sink.plz

@@ -0,0 +1,13 @@
+{
+  // a comment
+  foo: bar
+  bar: :foo
+  sky_is_blue: :boolean.not(false)
+  colors: { red green blue }
+  two: :integer.add(1)(1)
+  add_one: :integer.add(1)
+  three: :add_one(:two)
+  function: x => { value: :x }
+  conditional_value: :function({ @if :sky_is_blue :two :three })
+  side_effect: { @runtime context => :context.log("this goes to stderr") }
+}

examples/lookup-environment-variable.plz

@@ -0,0 +1,15 @@
+{@runtime context =>
+  :flow({
+    :context.arguments.lookup
+    :match({
+      none: {}
+      some: :flow({
+        :context.environment.lookup
+        :match({
+          none: {}
+          some: :identity
+        })
+      })
+    })
+  })(variable)
+}

src/examples.test.ts

@@ -0,0 +1,36 @@
+import { exec } from 'node:child_process'
+import { promises as fs } from 'node:fs'
+import path from 'node:path'
+import test, { suite } from 'node:test'
+
+const exampleDirectoryPath = path.join(import.meta.dirname, '..', 'examples')
+const pleasePath = path.join(
+  import.meta.dirname,
+  'language',
+  'cli',
+  'please.js',
+)
+
+suite('examples', async () => {
+  for (const exampleFileName of await fs.readdir(exampleDirectoryPath)) {
+    const exampleFilePath = path.join(exampleDirectoryPath, exampleFileName)
+    // TODO: Use snapshot testing instead of merely checking for errors.
+    test(
+      exampleFileName,
+      () =>
+        new Promise((resolve, reject) => {
+          const _childProcess = exec(
+            `cat "${exampleFilePath}" | node "${pleasePath}" --output-format=plz`,
+            (error, _stdout, _stderr) => {
+              // `error` is an `ExecError` when exit status is nonzero.
+              if (error !== null) {
+                reject(error)
+              } else {
+                resolve(undefined)
+              }
+            },
+          )
+        }),
+    )
+  }
+})