Require quotes around @ in atoms

This carves out syntax space for a planned generalized keyword
expression sugar (`@` will become relevant to parsing).

Author: mkantor

README.md

@@ -9,7 +9,7 @@ git clone [email protected]:mkantor/please-lang-prototype.git
 cd please-lang-prototype
 npm install
 npm run build
-echo '{@runtime, { context => :context.program.start_time }}' | ./please --output-format=json
+echo '{"@runtime", { context => :context.program.start_time }}' | ./please --output-format=json
 ```
 
 There are more example programs in [`./examples`](./examples).
@@ -45,7 +45,7 @@ data representation implied by the fact that a value is an atom (e.g. the atom
 `2` may be an integer in memory).
 
 Bare words not containing any
-[reserved character sequences](./src/language/parsing/atom.ts#L33-L55) are
+[reserved character sequences](./src/language/parsing/atom.ts#L34-L57) are
 atoms:
 
 ```
@@ -178,7 +178,7 @@ expressions_. Most of the interesting stuff that Please does involves evaluating
 keyword expressions.
 
 Under the hood, keyword expressions are modeled as objects. For example, `:foo`
-desugars to `{ @lookup, { key: foo } }`. All such expressions have a property
+desugars to `{ "@lookup", { key: foo } }`. All such expressions have a property
 named `0` referring to a value that is an `@`-prefixed atom (the keyword). Most
 keyword expressions also require a property named `1` to pass an argument to the
 expression. Keywords include `@apply`, `@check`, `@function`, `@if`, `@index`,
@@ -211,7 +211,7 @@ function from other programming languages, except there can be any number of
 `@runtime` expressions in a given program. Here's an example:
 
 ```
-{@runtime, { context => :context.program.start_time }}
+{"@runtime", { context => :context.program.start_time }}
 ```
 
 Unsurprisingly, this program outputs the current time when run.
@@ -250,7 +250,7 @@ Take this example `plz` program:
 {
   language: Please
   message: :atom.prepend("Welcome to ")(:language)
-  now: {@runtime, { context => :context.program.start_time }}
+  now: {"@runtime", { context => :context.program.start_time }}
 }
 ```
 
@@ -260,16 +260,16 @@ It desugars to the following `plo` program:
 {
   language: Please
   message: {
-    0: @apply
+    0: "@apply"
     1: {
       function: {
-        0: @apply
+        0: "@apply"
         1: {
           function: {
-            0: @index
+            0: "@index"
             1: {
               object: {
-                0: @lookup
+                0: "@lookup"
                 1: {
                   key: atom
                 }
@@ -283,25 +283,25 @@ It desugars to the following `plo` program:
         }
       }
       argument: {
-        0: @lookup
+        0: "@lookup"
         1: {
           key: language
         }
       }
     }
   }
   now: {
-    0: @runtime
+    0: "@runtime"
     1: {
       0: {
-        0: @function
+        0: "@function"
         1: {
           parameter: context
           body: {
-            0: @index
+            0: "@index"
             1: {
               object: {
-                0: @lookup
+                0: "@lookup"
                 1: {
                   key: context
                 }
@@ -326,17 +326,17 @@ Which in turn compiles to the following `plt` program:
   language: Please
   message: "Welcome to Please"
   now: {
-    0: @runtime
+    0: "@runtime"
     1: {
       function: {
-        0: @function
+        0: "@function"
         1: {
           parameter: context
           body: {
-            0: @index
+            0: "@index"
             1: {
               object: {
-                0: @lookup
+                0: "@lookup"
                 1: {
                   key: context
                 }
@@ -360,7 +360,7 @@ Which produces the following runtime output:
 {
   language: Please
   message: "Welcome to Please"
-  now: "2025-05-13T22:11:56.804Z"
+  now: "2025-05-13T22:47:50.802Z"
 }
 ```
 

examples/fibonacci.plz

@@ -1,6 +1,6 @@
 {
   fibonacci: n => {
-    @if
+    "@if"
     {
       condition: :n < 2
       then: :n
@@ -9,14 +9,14 @@
   }
 
   input: {
-    @runtime
+    "@runtime"
     { context => :context.arguments.lookup(input) }
   }
 
   output: :input match {
     none: _ => "missing input argument"
     some: input => {
-      @if
+      "@if"
       {
         condition: :natural_number.is(:input)
         then: :fibonacci(:input)

examples/kitchen-sink.plz

@@ -8,6 +8,6 @@
   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") } }
+  conditional_value: :function({ "@if", { :sky_is_blue, :two, :three } })
+  side_effect: { "@runtime", { context => :context.log("this goes to stderr") } }
 }

examples/lookup-environment-variable.plz

@@ -3,7 +3,7 @@
   * variable named `FOO`.
   */
 {
-  @runtime
+  "@runtime"
   {
     context =>
       :context.arguments.lookup(variable) match {

src/end-to-end.test.ts

@@ -28,21 +28,21 @@ testCases(endToEnd, code => code)('end-to-end tests', [
   ['{,a,b,c,}', either.makeRight({ 0: 'a', 1: 'b', 2: 'c' })],
   ['{a,1:overwritten,c}', either.makeRight({ 0: 'a', 1: 'c' })],
   ['{overwritten,0:a,c}', either.makeRight({ 0: 'a', 1: 'c' })],
-  ['{@check, {type:true, value:true}}', either.makeRight('true')],
+  ['{"@check", {type:true, value:true}}', either.makeRight('true')],
   [
-    '{@panic}',
+    '{"@panic"}',
     result => {
       assert(either.isLeft(result))
       assert('kind' in result.value)
       assert.deepEqual(result.value.kind, 'panic')
     },
   ],
-  ['{a:A, b:{@lookup, {a}}}', either.makeRight({ a: 'A', b: 'A' })],
-  ['{a:A, {@lookup, {a}}}', either.makeRight({ a: 'A', 0: 'A' })],
+  ['{a:A, b:{"@lookup", {a}}}', either.makeRight({ a: 'A', b: 'A' })],
+  ['{a:A, {"@lookup", {a}}}', either.makeRight({ a: 'A', 0: 'A' })],
   ['{a:A, b: :a}', either.makeRight({ a: 'A', b: 'A' })],
   ['{a:A, :a}', either.makeRight({ a: 'A', 0: 'A' })],
   [
-    '{@runtime, {_ => {@panic}}}',
+    '{"@runtime", {_ => {"@panic"}}}',
     result => {
       assert(either.isLeft(result))
       assert('kind' in result.value)
@@ -90,12 +90,12 @@ testCases(endToEnd, code => code)('end-to-end tests', [
       // foo: bar
       "static data":"blah blah blah"
       "evaluated data": {
-        0:@runtime
+        0:"@runtime"
         1:{
           function:{
-            0:@apply
+            0:"@apply"
             1:{
-              function:{0:@index, 1:{object:{0:@lookup, 1:{key:object}}, query:{0:lookup}}}
+              function:{0:"@index", 1:{object:{0:"@lookup", 1:{key:object}}, query:{0:lookup}}}
               argument:"key which does not exist in runtime context"
             }
           }
@@ -153,7 +153,7 @@ testCases(endToEnd, code => code)('end-to-end tests', [
   ],
   [':match({ a: A })({ tag: a, value: {} })', either.makeRight('A')],
   [
-    `{@runtime, { context =>
+    `{"@runtime", { context =>
       :identity(:context).program.start_time
     }}`,
     output => {
@@ -181,7 +181,7 @@ testCases(endToEnd, code => code)('end-to-end tests', [
   [`(1 - 2) - 3`, either.makeRight('-4')],
   [':flow(:atom.append(b))(:atom.append(a))(z)', either.makeRight('zab')],
   [
-    `{@runtime
+    `{"@runtime"
       { :object.lookup("key which does not exist in runtime context") }
     }`,
     either.makeRight({ tag: 'none', value: {} }),
@@ -213,7 +213,7 @@ testCases(endToEnd, code => code)('end-to-end tests', [
     either.makeRight({ true: 'true', false: 'false' }),
   ],
   [
-    `{@runtime, {
+    `{"@runtime", {
       :flow(
         :match({
           none: "environment does not exist"
@@ -260,7 +260,7 @@ testCases(endToEnd, code => code)('end-to-end tests', [
     either.makeRight({ 0: 'a', 1: 'b', 2: 'c', 3: 'd' }),
   ],
   [
-    `{@runtime, { context =>
+    `{"@runtime", { context =>
       :context.environment.lookup(PATH)
     }}`,
     output => {
@@ -273,10 +273,10 @@ testCases(endToEnd, code => code)('end-to-end tests', [
     },
   ],
   [
-    `{@if, {
+    `{"@if", {
       true
       "it works!"
-      {@panic}
+      {"@panic"}
     }}`,
     either.makeRight('it works!'),
   ],
@@ -289,19 +289,19 @@ testCases(endToEnd, code => code)('end-to-end tests', [
     either.makeRight({ 0: 'a', 1: 'b', 2: 'c' }),
   ],
   [
-    `{@runtime, { context =>
-      {@if, {
+    `{"@runtime", { context =>
+      {"@if", {
         :boolean.not(:boolean.is(:context))
         "it works!"
-        {@panic}
+        {"@panic"}
       }}
     }}`,
     either.makeRight('it works!'),
   ],
   [
     `{
       fibonacci: n => {
-        @if, {
+        "@if", {
           :integer.less_than(2)(:n)
           then: :n
           else: :fibonacci(:n - 1) + :fibonacci(:n - 2)
@@ -362,7 +362,7 @@ testCases(endToEnd, code => code)('end-to-end tests', [
     either.makeRight('2'),
   ],
   [
-    `{@runtime, { context =>
+    `{"@runtime", { context =>
       (
         PATH
           |> :context.environment.lookup

src/language/compiling/unparsing.test.ts

@@ -24,7 +24,7 @@ testCases(
   [{}, either.makeRight('{}')],
   ['a', either.makeRight('a')],
   ['Hello, world!', either.makeRight('"Hello, world!"')],
-  ['@test', either.makeRight('@test')],
+  ['@test', either.makeRight('"@test"')],
   [{ 0: 'a' }, either.makeRight('{ a }')],
   [{ 1: 'a' }, either.makeRight('{ 1: a }')],
   [
@@ -87,7 +87,7 @@ testCases(
       },
     },
     either.makeRight(
-      '{ @runtime, { context => :context.program.start_time } }',
+      '{ "@runtime", { context => :context.program.start_time } }',
     ),
   ],
   [
@@ -118,7 +118,7 @@ testCases(
   [{}, either.makeRight('{}')],
   ['a', either.makeRight('a')],
   ['Hello, world!', either.makeRight('"Hello, world!"')],
-  ['@test', either.makeRight('@test')],
+  ['@test', either.makeRight('"@test"')],
   [{ 0: 'a' }, either.makeRight('{\n  a\n}')],
   [{ 1: 'a' }, either.makeRight('{\n  1: a\n}')],
   [
@@ -183,7 +183,7 @@ testCases(
       },
     },
     either.makeRight(
-      '{\n  @runtime\n  {\n    context => :context.program.start_time\n  }\n}',
+      '{\n  "@runtime"\n  {\n    context => :context.program.start_time\n  }\n}',
     ),
   ],
   [

src/language/parsing/atom.ts

@@ -11,6 +11,7 @@ import {
   zeroOrMore,
 } from '@matt.kantor/parsing'
 import {
+  atSign,
   backslash,
   closingBlockCommentDelimiter,
   closingBrace,
@@ -31,6 +32,7 @@ import { whitespace } from './trivia.js'
 export type Atom = string
 
 const atomComponentsRequiringQuotation = [
+  atSign,
   backslash,
   closingBlockCommentDelimiter,
   closingBrace,

src/language/parsing/literals.ts

@@ -2,6 +2,7 @@ import { literal } from '@matt.kantor/parsing'
 
 export const arrow = literal('=>')
 export const asterisk = literal('*')
+export const atSign = literal('@')
 export const backslash = literal('\\')
 export const closingBlockCommentDelimiter = literal('*/')
 export const closingBrace = literal('}')