Change how keyword expression argments are encoded

Previously arguments were additional properties at the top level of the
keyword expression object (siblings of the `0` property). Now they are
packed into a single property value keyed by `1`.

This brings keyword expressions semantics closer to function semantics
(both now have a single argument), and will help make the upcoming
generalized keyword expression syntax sugar more sensible.

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).
@@ -178,10 +178,11 @@ 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 key `0`
-referring to a value that is an `@`-prefixed atom (the keyword). Keywords
-include `@apply`, `@check`, `@function`, `@if`, `@index`, `@lookup`, `@panic`,
-and `@runtime`.
+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`,
+`@lookup`, `@panic`, and `@runtime`.
 
 Currently only `@function`, `@lookup`, `@index`, and `@apply` have syntax
 sugars.
@@ -210,7 +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.
@@ -249,7 +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 }}
 }
 ```
 
@@ -260,39 +261,57 @@ It desugars to the following `plo` program:
   language: Please
   message: {
     0: @apply
-    function: {
-      0: @apply
+    1: {
       function: {
-        0: @index
-        object: {
-          0: @lookup
-          key: atom
+        0: @apply
+        1: {
+          function: {
+            0: @index
+            1: {
+              object: {
+                0: @lookup
+                1: {
+                  key: atom
+                }
+              }
+              query: {
+                0: prepend
+              }
+            }
+          }
+          argument: "Welcome to "
         }
-        query: {
-          0: prepend
+      }
+      argument: {
+        0: @lookup
+        1: {
+          key: language
         }
       }
-      argument: "Welcome to "
-    }
-    argument: {
-      0: @lookup
-      key: language
     }
   }
   now: {
     0: @runtime
     1: {
-      0: @function
-      parameter: context
-      body: {
-        0: @index
-        object: {
-          0: @lookup
-          key: context
-        }
-        query: {
-          0: program
-          1: start_time
+      0: {
+        0: @function
+        1: {
+          parameter: context
+          body: {
+            0: @index
+            1: {
+              object: {
+                0: @lookup
+                1: {
+                  key: context
+                }
+              }
+              query: {
+                0: program
+                1: start_time
+              }
+            }
+          }
         }
       }
     }
@@ -308,18 +327,26 @@ Which in turn compiles to the following `plt` program:
   message: "Welcome to Please"
   now: {
     0: @runtime
-    function: {
-      0: @function
-      parameter: context
-      body: {
-        0: @index
-        object: {
-          0: @lookup
-          key: context
-        }
-        query: {
-          0: program
-          1: start_time
+    1: {
+      function: {
+        0: @function
+        1: {
+          parameter: context
+          body: {
+            0: @index
+            1: {
+              object: {
+                0: @lookup
+                1: {
+                  key: context
+                }
+              }
+              query: {
+                0: program
+                1: start_time
+              }
+            }
+          }
         }
       }
     }
@@ -333,7 +360,7 @@ Which produces the following runtime output:
 {
   language: Please
   message: "Welcome to Please"
-  now: "2025-02-14T18:45:14.168Z"
+  now: "2025-05-13T22:11:56.804Z"
 }
 ```
 

examples/fibonacci.plz

@@ -1,23 +1,27 @@
 {
   fibonacci: n => {
     @if
-    condition: :n < 2
-    then: :n
-    else: :fibonacci(:n - 1) + :fibonacci(:n - 2)
+    {
+      condition: :n < 2
+      then: :n
+      else: :fibonacci(:n - 1) + :fibonacci(:n - 2)
+    }
   }
 
   input: {
     @runtime
-    context => :context.arguments.lookup(input)
+    { context => :context.arguments.lookup(input) }
   }
 
   output: :input match {
     none: _ => "missing input argument"
     some: input => {
       @if
-      condition: :natural_number.is(:input)
-      then: :fibonacci(:input)
-      else: "input must be a natural number"
+      {
+        condition: :natural_number.is(:input)
+        then: :fibonacci(:input)
+        else: "input must be a natural number"
+      }
     }
   }
 }.output

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

@@ -4,12 +4,14 @@
   */
 {
   @runtime
-  context =>
-    :context.arguments.lookup(variable) match {
-      none: {}
-      some: :context.environment.lookup >> :match({
+  {
+    context =>
+      :context.arguments.lookup(variable) match {
         none: {}
-        some: :identity
-      })
-    }
+        some: :context.environment.lookup >> :match({
+          none: {}
+          some: :identity
+        })
+      }
+  }
 }