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authorOri Bernstein <orib@google.com>2012-06-29 17:56:32 -0400
committerOri Bernstein <orib@google.com>2012-06-29 17:56:32 -0400
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downloadmc-ce977b34a1f6449114772a41a4677e2118830e92.tar.gz
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+ The Myrddin Programming Language
+ Jun 2012
+ Ori Bernstein
+
+Overview:
+
+ Myrddin is designed to be a simple, low level programming
+ language. It is designed to provide the programmer with
+ predictable behavior and a transparent compilation model,
+ while at the same time providing the benefits of strong
+ type checking, generics, type inference, and similar.
+ Myrddin is not a language designed to explore the forefront
+ of type theory, or compiler technology. It is not a language
+ that is focused on guaranteeing perfect safety. It's focus
+ is on being a practical, small, fairly well defined, and
+ easy to understand language for work that needs to be close
+ to the hardware.
+
+Introduction:
+
+ We begin with the archetypical "Hello world" example, deconstructing
+ it as we go:
+
+ use std
+
+ const main = {
+ /* say hello */
+ std.write(1, "Hello World\n")
+ }
+
+ The first line, `use std`, tells the compiler to import the standard
+ library, which at the time of this writing only barely exists as a
+ copy-paste group of files that works only on Linux, implementing almost
+ no useful functions. One of the functions that it does provide,
+ however, is the 'write' system call.
+
+ The next line, 'const main = ...' declares a constant value called
+ 'main'. These constant values must be initialized at their declaration
+ to a literal value. In this case, it is intialized to a constant
+ function '{;std.write(1, "Hello World\n");}'
+
+ In Myrddin, all functions begin with a '{', followed by a list
+ of arguments, which is terminated by a newline (or semicolon. The
+ two are equivalent). This is followed by any number of statements,
+ and closed by a '}'.
+
+ The text '/* say hello */' is a comment. It is ignored by the compiler,
+ and is used to add useful information for the programmer. In Myrddin,
+ unlike many popular languages, comments nest. This makes code like
+ /* outer /* inner coment */ comment */ valid.
+
+ The text 'std.write' refers the 'write' function from the 'std' library.
+ In Myrddin, a name can belong to an imported namespace. The language,
+ for reasons of parsimony, only allows one level of namespace. I saw
+ Java package names and ran screaming in horror, possibly too far to
+ the other extreme. This function is statically typed, taking a single
+ integer argument, and a byte slice to write.
+
+ The text '(1, "Hello World)' is the function call itself. It takes
+ the literal "1", and the byte slice "Hello World\n", and calls the
+ function 'std.write' with them as arguments.
+
+ It would be useful now to specify that the value '1' is an integer-like
+ constant, but it is not an integer. It is polymorphic, and can be used
+ at any point where a value of any integer type is needed.
+
+Declarations:
+
+ In Myrddin, declarations take the following form:
+
+ var|const|generic name [: type] [= expr]
+
+ To give a few examples:
+
+ var x
+ var foo : int
+ const c = 123
+ const pi : float32 = 3.1415
+ generic id : (@a -> @a) = {a:@a -> @a; -> a}
+
+ The first example, 'var x', declares a variable named x. The type is not
+ set explicitly, but it will be determined by the compiler (or the code
+ will fail to compile, saying that the type of the variable could not
+ be determined).
+
+ The second example, 'var foo : int' explicitly sets the type of a
+ variable named 'foo' to an integer. It does not initialize it. However,
+ it is [FIXME: make this not a lie] a compilation error to use a
+ variable without prior intialization, so this is not dangerous.
+
+ The third example, 'cosnt c = 123' declares a constant named c,
+ and initializes it to the value 123. All constants require initializers,
+ as they cannot be assigned to later in the code.
+
+ The fourth example, 'const pi : float32 = 3.1415', shows the full form
+ of declarations. It includes both the type and initializer components.
+
+ The final "overdeclared" example declares a generic function called
+ 'id', which takes any type '@a' and returns the same type. It is
+ initialized to a function which specifies these types again, and
+ has a body that returns it's argument. This is not idiomatic code,
+ and is only provided as an example of what is possible. The normal
+ declaration would look something like this:
+
+ generic id = {a:@a; -> a}
+
+Types:
+
+ Myrddin comes with a large number of built in types. These are
+ listed below:
+
+ void
+ The void type. This type represents an empty value.
+ For reasons of consistency when specializing generics, void
+ values can be created, assigned to, and manipulated like
+ any other value.
+
+ bool
+ A Boolean type. The value of this is either 'true' (equivalent
+ to any non-zero) or 'false', equivalent to a zero value. The
+ size of this type is undefined.
+
+ char
+ A value representing a single code point in the default
+ encoding. The encoding is undefined, and the value of the
+ character is opaque.
+
+
+ int8 int16 int32 int64 int
+ uint8 uint16 uint32 uint64 uint
+ Integer types. For the above types, the number at the end
+ represents the size of the type. The ones without a number at
+ the end are of undefined type. These values can be assumed to
+ be in two's complement. The semantics of overflowing are yet to
+ be specified.
+
+ float32 float64
+ Floating-point types. The exact semantics are yet to be
+ defined.
+
+ @<ident>
+ A generic type. This is only allowed in the scope of 'generic'
+ constants.
+
+ It also allows composite types to be defined. These are listed below:
+
+ @a
+
+Constants:
+