ref: ac187c5de6db760389b4c47c36650fbc20465488
parent: 74c20890c23bd5047330e52c062f9fa10ede6e7f
author: Ori Bernstein <ori@eigenstate.org>
date: Wed Jan 18 16:24:58 EST 2017
Update the section on structure.
--- a/doc/lang.txt
+++ b/doc/lang.txt
@@ -1,29 +1,38 @@
The Myrddin Programming Language
Jul 2012
- Updated Dec 2015
+ Updated Dec 2016
Ori Bernstein
TABLE OF CONTENTS:
1. ABOUT
- 2. NOTATION AND SEMANTICS
- 2.1. Grammar
+ 2. LEXICAL CONVENTIONS
+ 2.1. EBNF-ish
2.2. As-If Rule
- 3. LEXICAL CONVENTIONS
- 3.1. Summary
- 4. SYNTAX
- 4.1. Declarations
- 4.2. Literal Values
- 4.3. Blocks
- 4.4. Control Constructs
- 4.5. Expressions
- 4.6. Packages and Uses
- 5. TYPES
- 5.1. Data Types
- 5.2. Type Inference
- 5.3. Traits
- 5.4. Generics
- 6. GRAMMAR
+ 3. STRUCTURE:
+ 3.1. Whitespace and Keywords
+ 3.2. File Structure
+ 3.3. Declarations
+ 3.4. Packages and Uses
+ 3.5. Scoping
+ 4. TYPES
+ 4.1. Type Definitions
+ 4.2. Traits and Impls
+ 4.3. Generics
+ 4.4. Type Inference
+ 5. VALUES AND EXPRESSIONS
+ 5.1. Declarations
+ 5.2. Literal Values
+ 5.3. Control Constructs
+ 5.4. Expressions
+ 5.6. Packages and Uses
+ 6. CONTROL FLOW
+ 6.1. Blocks
+ 6.2. Conditionals
+ 6.3. Matches
+ 6.4. Looping
+ 6.5. Goto
+ 7. GRAMMAR
1. ABOUT:
@@ -43,9 +52,9 @@
ML, with ideas from too many other places to name.
-2. NOTATION AND SEMANTICS:
+2. LEXICAL CONVENTIONS:
- 2.1. Grammar:
+ 2.1. EBNF-ish:
Syntax is defined using an informal variant of EBNF.
@@ -81,9 +90,9 @@
as long as the result is observed as if the semantics specified were
followed strictly.
-3. LEXICAL CONVENTIONS:
+3. STRUCTURE:
- 3.1. Summary:
+ 3.1. Whitespace and Keywords:
The language is composed of several classes of tokens. There are
comments, identifiers, keywords, punctuation, and whitespace.
@@ -123,10 +132,49 @@
interchangable. They both are used to mark the end of logical lines,
and will be uniformly referred to as line terminators.
-4. SYNTAX OVERVIEW:
+ 3.2. File Structure:
- 4.1. Declarations:
+ file: (decl | package | use | implstmt | traitdef | tydef)*
+ A file is composed of a sequence of top level elements. These
+ top level elements consist of:
+
+ - Declarations:
+
+ These define a constant or a variable. It's worth noting
+ that Myrddin has no special syntax for declaring functions,
+ but instead assigns a closure to a variable or constant.
+
+ - Package Definitions:
+
+ These define the list of exported values from a file. As
+ part of compilation, all the exported names from a package
+ will get merged together from all the files being built
+ into that package.
+
+ - Use Statements:
+
+ These import symbols for use within the file. These symbols
+ come from either installed packages or files within the
+ project being compiled.
+
+ - Type Definitions:
+
+ These define new types.
+
+ - Trait Definitions:
+
+ These define traits, which are attributes on types that
+ may be implemented by impl functions. They define required
+ functions on the type.
+
+ - Impl Statements:
+
+ These define implementations of traits, allowing an
+ existing trait to be attached to an existing type.
+
+ 3.3. Declarations:
+
decl: attrs ("var" | "const" | "generic") decllist attrs: ("exern" | "pkglocal" | "$noret")+ decllist: declbody ("," declbody)*@@ -204,7 +252,106 @@
}
+ 3.4. Packages and Uses
+ bareuse: use ident
+ quoteuse: use "<quoted string>"
+ pkgdef: "pkg" ident = decl* ";;"
+
+
+ There are two keywords for module system. 'use' is the simpler
+ of the two, and has two cases:
+
+ use syspkg
+ use "localfile"
+
+ The first form, which does not have the package name quoted, will
+ search the system include paths for the package listed. It does not
+ search relative to the file or the compiler working directory.
+
+ The quoted form searches the current directory for a use file named
+ "localpkg" and imports it.
+
+ The 'pkg' keyword allows you to define a (partial) package by
+ listing the symbols and types for export. For example,
+
+ pkg mypkg =
+ type mytype
+
+ const Myconst : int = 42
+ const myfunc : (v : int -> bool)
+ ;;
+
+ declares a package "mypkg", which defines three exports, "mytype",
+ "Myconst", and "myfunc". The definitions of the values may be
+ defined in the 'pkg' specification, but it is preferred to implement
+ them in the body of the code for readability. Scanning the export
+ list is desirable from a readability perspective.
+
+ 3.5. Scoping:
+
+ Myrddin is a lexically scoped language, with namespaces and types
+ defined in a way that facilitates separate compilation with minimal
+ burden on the linker.
+
+ In Myrddin, declarations may appear in any order, and be used at any
+ point at which it is in scope. Any global symbols are initialized
+ before the program begins. Any nonglobal symbols are initialized
+ on the line where they are defined. This decision allows for slightly
+ strange code, but allows for mutually recursive functions with no
+ forward declarations or special cases.
+
+ 3.5.1. Scope Rules:
+
+ Myrddin follows the usual lexical scoping rules. A variable
+ may be defined on any line in the program. From there, any
+ expressions within that block and its sub blocks may refer
+ to it.
+
+ The variables declared in constructs starting a block are
+ scoped to that block. For example, in `for var i = 0; ...`,
+ the variable `i` is scoped to the body of the for loop.
+ In the function `{x, y; funcbody()}`, the variables `x` and+ `y` are scoped to the body of the function.
+
+ Variables may shadow other variables, with the exception of
+ captured variables in pattern matches. The rules for matches
+ are covered in depth in section 6.3, but the rationale for
+ this is to prevent ambiguity when matching against defined
+ constants.
+
+ 3.5.2. Capturing Variables:
+
+ When a closure is created, it captures all of the variables
+ that it refers to in its scope by value. This allows for
+ simple heapification of the closure.
+
+ For example:
+
+ var x = 1
+ var closure = {; -> x}+ x++
+ std.put("x: {}, closure(): {}\n", x, closure())+
+ should output:
+
+ x: 2, closure(): 1
+
+ 3.5.2. Namespaces:
+
+ A namespace introduced by importing a package is gramatically
+ equivalent to a struct member lookup. The namespace is not
+ optional.
+
+ 3.6. Program Initialization:
+
+ Any file may define a single function name `__init__`. This function
+ will be invoked before `main` runs, and after the `__init__ `function
+ for all files included through use statements.
+
+
+4. VALUES AND EXPRESSIONS:
+
4.3. Literal Values
4.3.1. Atomic Literals:
@@ -540,7 +687,13 @@
postfixexpr: <prefixop> postfixexpr
prefixexpr: atomicexpr <unaryop>
- Myrddin expressions should be fairly familiiar to most programmers.
+ Myrddin expressions should be fairly familiar to most programmers.
+ Expressions are represented by a precedence sorted heirarchy of
+ binary operators. These operators operate on prefix expressions,
+ which in turn operate on postfix expressions. And postfix
+ expressions operate on parenthesized expressions, literals, or
+ values.
+
The operators are listed below in order of precedence, and a short
summary of what they do is listed given. For the sake of clarity, 'x'
will stand in for any expression composed entirely of subexpressions
@@ -653,6 +806,9 @@
match, again, given that it is never read from in the body of the
match.
+ An represents a location in the machine that can be stored
+ to persistently and manipulated by the programmer. An obvious
+ example of this would be a variable name, although
4.6.3. Cast Expressions:
@@ -747,6 +903,8 @@
4.6.4. Assignment:
+ The assignment operators
+
4.6.5. Bitwise Expressions:
4.6.6: Arithmetic Expressons:
@@ -754,45 +912,6 @@
4.6.7: Postfix Expressiosn:
4.6.8: Prefix Expressions
-
-
- 4.8. Packages and Uses:
-
- bareuse: use ident
- quoteuse: use "<quoted string>"
- pkgdef: "pkg" ident = decl* ";;"
-
-
- There are two keywords for module system. 'use' is the simpler
- of the two, and has two cases:
-
- use syspkg
- use "localfile"
-
- The first form, which does not have the package name quoted, will
- search the system include paths for the package listed. It does not
- search relative to the file or the compiler working directory.
-
- The quoted form searches the current directory for a use file named
- "localpkg" and imports it.
-
- The 'pkg' keyword allows you to define a (partial) package by
- listing the symbols and types for export. For example,
-
- pkg mypkg =
- type mytype
-
- const Myconst : int = 42
- const myfunc : (v : int -> bool)
- ;;
-
- declares a package "mypkg", which defines three exports, "mytype",
- "Myconst", and "myfunc". The definitions of the values may be
- defined in the 'pkg' specification, but it is preferred to implement
- them in the body of the code for readability. Scanning the export
- list is desirable from a readability perspective.
-
- 4.9. Scoping and Namespaces:
5. TYPES: