145 lines
3.3 KiB
Markdown
145 lines
3.3 KiB
Markdown
# Syntax
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This document describes the ginger syntax and data-structures, and how they are
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evaluated.
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# Goals
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I have some immediate goals I'm trying to achieve with this syntax:
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* Everything is strings (except numbers, functions, and composites). There is no
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symbol type, atom type, keyword type, etc... they're all just strings.
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* There is no `defmacro`. Macro creation and usage is simply an inherent feature
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of the language syntax.
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# Walkthrough
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This is a number which evalutates to 5:
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```
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5
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```
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This is a string, it can contain anything:
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```
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"! I'm the king of the world !"
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```
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This is a list. It evaluates to a linked-list of four strings:
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```
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("a" "b" "c" "d")
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```
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This is a vector of those same elements. It's like a list, but has some slightly
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different properties. We'll mostly be using lists:
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```
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["a" "b" "c" "d"]
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```
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This is a string
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```
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"+"
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```
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`:` is the evaluator. A string beginning with `:` is evaluated to whatever it
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references. This evaluates to a function which adds its arguments:
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```
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":+"
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```
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This evaluates to list whose elements are a function and two numbers:
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```
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(":+" 1 2)
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```
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A list whose first element is a `:` calls the second element as a function with
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the rest of the elements as arguments. This evaluates to the number 5:
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```
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(":" ":+" 1 2)
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```
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A bare string (lacking in `"`) is automatically prefixed with a `:`, if it
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doesn't already have one. So `":+"`, `:+`, and `+`, are equivalent. `":"` and
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`:` are also equivalent. This is equivalent to the previous example:
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```
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(: + 1 2)
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```
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The `fn` function can be used to define a new function. Note the `.` instead of
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`:`. We'll cover that in a bit. This evaluates to an anonymous function which
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adds one to its argument and returns it:
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```
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(. fn [x]
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(: + x 1))
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```
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The `def` function can be used to bind some value to a new variable. This
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defines a variable `foo` which evaluates to the string `"bar"`:
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```
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(. def foo "bar")
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```
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This defines a variable `incr` which evaluates to a function which adds one to
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its argument:
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```
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(. def incr
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(. fn [x]
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(: + x 1)))
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```
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This uses `defn` as a shortcut for the above:
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```
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(. defn incr [x]
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(: + x 1))
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```
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There are also maps. A map's keys can be any value(?). A map's values can be any
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value. This evaluates to a map with 2 key/val pairs:
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```
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{ "foo" foo
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"bar" (: incr 4) }
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```
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`.` is the half-evaluator. It only works on lists, and runs the function given
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in the first argument with the unevaluated arguments (even if they have `:`).
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You can generate new code to run (compile-time macros) using the normal `fn`.
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The returned value is evaluated in place of the original. This evaluates to a
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`let`-like function, except it forces you to use the capitalized variable names
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in the body (utterly useless):
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```
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#
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# map-alternate is a made up function which maps over every other element in a
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# list, starting with the first.
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# E.g. (: map-alternate (. fn [x] (: + x 1)) (1 2 3 4 5)) -> (2 2 4 4 6)
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#
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# capitalize is a made up function which looks for the first letter in a string
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# and capitalizes it
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#
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(. defn caplet [mapping body...]
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("." let
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(: map-alternate
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(. fn [x] (: capitalize x))
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mapping)
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body...))
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#Usage
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(. caplet [foo "this is foo"
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dog "this is dog"]
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(: println Foo)
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(: println Dog))
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```
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