ginger/docs/syntax.md

# Syntax

This document describes the ginger syntax and data-structures, and how they are
evaluated.

# Goals

I have some immediate goals I'm trying to achieve with this syntax:

* Everything is strings (except numbers, functions, and data structures). There
  is no symbol type, atom type, keyword type, etc... they're all just strings.

* There is no `defmacro`. Macro creation and usage is simply an inherent feature
  of the language syntax.

# Walkthrough

This is a number which evalutates to 5:

```
5
```

This is a string, it can contain anything:

```
"! I'm the king of the world !"
```

This is a list. It evaluates to a linked-list of four strings:

```
("a" "b" "c" "d")
```

This is a vector of those same elements. It's like a list, but has some slightly
different properties. We'll mostly be using lists:

```
["a" "b" "c" "d"]
```

This is a string

```
"+"
```

`:` is the evaluator. A string beginning with `:` is evaluated to whatever it
references. This evaluates to a function which adds its arguments:

```
":+"
```

This evaluates to list whose elements are a function and two numbers:

```
(":+" 1 2)
```

A list whose first element is a `:` calls the second element as a function with
the rest of the elements as arguments. This evaluates to the number 5:

```
(":" ":+" 1 2)
```

A bare string (lacking in `"`) is automatically prefixed with a `:`, if it
doesn't already have one. So `":+"`, `:+`, and `+`, are equivalent. `":"` and
`:` are also equivalent. This is equivalent to the previous example:

```
(: + 1 2)
```

The `fn` function can be used to define a new function. Note the `.` instead of
`:`. We'll cover that in a bit. This evaluates to an anonymous function which
adds one to its argument and returns it:

```
(. fn [x]
    (: + x 1))
```

The `def` function can be used to bind some value to a new variable. This
defines a variable `foo` which evaluates to the string `"bar"`:

```
(. def foo "bar")
```

This defines a variable `incr` which evaluates to a function which adds one to
its argument:

```
(. def incr
    (. fn [x]
        (: + x 1)))
```

This uses `defn` as a shortcut for the above:
```
(. defn incr [x]
    (: + x 1))
```

There are also maps. A map's keys can be any value(?). A map's values can be any
value. This evaluates to a map with 2 key/val pairs:

```
{ "foo" foo
  "bar" (: incr 4) }
```

`.` is the half-evaluator. It only works on lists, and runs the function given
in the first argument with the unevaluated arguments (even if they have `:`).
You can generate new code to run on the fly (macros) using the normal `fn`. This
evaluates to a `let`-like function, except it forces you to use the capitalized
variable names in the body (utterly useless):

```
#
# eval evaluates a given value (either a string or list). It has been
# implicitely called on all examples so far.
#
# elem-map maps over every element in a list, embedded or otherwise
#
# capitalize looks for the first letter in a string and capitalizes it
#
(. defn caplet [mapping body...]
    (. eval
        (. let
            (: elem-map
                (. fn [x]
                    (. if (: mapping (: slice x 1))
                        (: capitalize x)
                        x))
                mapping)
            body...)))

#Usage
(. caplet [foo "this is foo"
           dog "this is dog"]
    (: println Foo)
    (: println Dog))
```