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author | Ori Bernstein <ori@eigenstate.org> | 2017-01-17 23:43:31 -0800 |
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committer | Ori Bernstein <ori@eigenstate.org> | 2017-01-17 23:43:31 -0800 |

commit | 74c20890c23bd5047330e52c062f9fa10ede6e7f (patch) | |

tree | d756515dea3b1dbef569fa26d95ca567362c0b31 /doc | |

parent | 10c5a7f3c6bd6d8c52a42f3d7ffb64eed6edf677 (diff) | |

download | mc-74c20890c23bd5047330e52c062f9fa10ede6e7f.tar.gz |

Add description of casts.

Diffstat (limited to 'doc')

-rw-r--r-- | doc/lang.txt | 347 |

1 files changed, 241 insertions, 106 deletions

diff --git a/doc/lang.txt b/doc/lang.txt index 4e9abab..a70067e 100644 --- a/doc/lang.txt +++ b/doc/lang.txt @@ -534,93 +534,234 @@ TABLE OF CONTENTS: 4.6. Expressions: - Myrddin expressions should be fairly familiiar to most programmers. - 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 - with higher precedence than the current current operator. 'e' will - stand in for any expression. Unless marked otherwise, expressions are - left associative. - - Precedence 12: - x.name Member lookup - x++ Postincrement - x-- Postdecrement - x# Dereference - x[e] Index - x[lo:hi] Slice - x(arg,list) Call - - Precedence 11: - ++x Preincrement - --x Predecrement - &x Address - !x Logical negation - ~x Bitwise negation - +x Positive (no operation) - -x Negate x - - Precedence 10: - x << y Shift left - x >> y Shift right - - Precedence 9: - x * y Multiply - x / y Divide - x % y Modulo - - Precedence 8: - x + y Add - x - y Subtract - - Precedence 7: - x & y Bitwise and - - Precedence 6: - x | y Bitwise or - x ^ y Bitwise xor - - Precedence 5: - `Name x Union construction - - Precedence 4: - x == x Equality - x != x Inequality - x > x Greater than - x >= x Greater than or equal to - x < x Less than - x <= x Less than or equal to - - Precedence 3: - x && y Logical and - - Precedence 2: - x || y Logical or - - Precedence 1: - x = y Assign Right assoc - x += y Fused add/assign Right assoc - x -= y Fused sub/assign Right assoc - x *= y Fused mul/assign Right assoc - x /= y Fused div/assign Right assoc - x %= y Fused mod/assign Right assoc - x |= y Fused or/assign Right assoc - x ^= y Fused xor/assign Right assoc - x &= y Fused and/assign Right assoc - x <<= y Fused shl/assign Right assoc - x >>= y Fused shr/assign Right assoc - - Precedence 0: - -> x Return expression - - All expressions on integers act on two's complement values which wrap - on overflow. Right shift expressions fill with the sign bit on signed - types, and fill with zeros on unsigned types. + 4.6.1. Summary and Precedence: + + expr: expr <binop> expr | prefixexpr | postfixexpr + postfixexpr: <prefixop> postfixexpr + prefixexpr: atomicexpr <unaryop> + + Myrddin expressions should be fairly familiiar to most programmers. + 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 + with higher precedence than the current current operator. 'e' will + stand in for any expression. Unless marked otherwise, expressions are + left associative. + + Precedence 13: + x Atomic expression + literal Atomic expression + (expr) Atomic expression + + Precedence 12: + x.name Member lookup + x++ Postincrement + x-- Postdecrement + x# Dereference + x[e] Index + x[lo:hi] Slice + x(arg,list) Call + + Precedence 11: + ++x Preincrement + --x Predecrement + &x Address + !x Logical negation + ~x Bitwise negation + +x Positive (no operation) + -x Negate x + + Precedence 10: + x << y Shift left + x >> y Shift right + + Precedence 9: + x * y Multiply + x / y Divide + x % y Modulo + + Precedence 8: + x + y Add + x - y Subtract + + Precedence 7: + x & y Bitwise and + + Precedence 6: + x | y Bitwise or + x ^ y Bitwise xor + + Precedence 5: + `Name x Union construction + + Precedence 4: + x == x Equality + x != x Inequality + x > x Greater than + x >= x Greater than or equal to + x < x Less than + x <= x Less than or equal to + + Precedence 3: + x && y Logical and + + Precedence 2: + x || y Logical or + + Precedence 1: + x = y Assign Right assoc + x += y Fused add/assign Right assoc + x -= y Fused sub/assign Right assoc + x *= y Fused mul/assign Right assoc + x /= y Fused div/assign Right assoc + x %= y Fused mod/assign Right assoc + x |= y Fused or/assign Right assoc + x ^= y Fused xor/assign Right assoc + x &= y Fused and/assign Right assoc + x <<= y Fused shl/assign Right assoc + x >>= y Fused shr/assign Right assoc + + Precedence 0: + -> x Return expression + + 4.6.2. Atomic Expressions: + + atomicexpr: ident | gap | literal | "(" expr ")" | + "sizeof" "(" type ")" | castexpr + castexpr: "(" expr ":" type ")" + gap: "_" + + Atomic expressions are the building blocks of expressions, and + are either parenthesized expressions or directly represent + literals. Literals are covered in depth in section 4.2. + + An identifier specifies a variable, and are looked up via + the scoping rules specified in section 4.9. + + Gap expressions (`_`) represent an anonymous sink value. Anything + can be assigned to a gap, and it may be used in pattern matching. + It is equivalent to creating a new temporary that is never read + from whenever it is used. For example: + + _ = 123 + + is equivalent to: + + var anon666 = 123 + + In match contexts, it is equivalent to a fresh variable in the + match, again, given that it is never read from in the body of the + match. + + + 4.6.3. Cast Expressions: + + Cast expressions convert a value from one type to another. + Casting proceeds according to the following rules: + + + SType DType Action + ------------------------------------------------------------- + int/int Conversions + ------------------------------------------------------------- + intN intK If n < k, sign extend the source + type, filling the top bits with the + sign bit of the source until it is the + same width as the destination type. + + if n > k, truncate the top bits of the + source to the width of the destination + type. + + uintN uintK If n < k, zero extend the source + type, filling the top bits with zero + until it is the same width as the + destination type. + + If n > k, truncate the top bits of the + source to the width of the destination + type. + ------------------------------------------------------------- + int/float conversions + ------------------------------------------------------------- + intN fltN The closest representable integer value + to the source should be stored in the + destination. + + uintN fltN The closest representable integer value + to the source should be stored in the + destination. + + fltN intN The closest representable integer value + to the source should be stored in the + destination. + + fltN uintN The closest representable integer value + to the source should be stored in the + destination. + ------------------------------------------------------------- + int/pointer conversions + ------------------------------------------------------------- + intN T# Extend the source value to the width + of a pointer in bits in an implementation + defined manner. + + uintN T# Extend the source value to the width + of a pointer in bits in an implementation + defined manner. + + T# intN Convert the address of the pointer to an + integer in an implementation specified + manner. There should exist at least one + integer type for which this conversion + will round trip. + + T# uintN Convert the address of the pointer to an + integer in an implementation specified + manner. There should exist at least one + integer type for which this conversion + will round trip. + ------------------------------------------------------------- + pointer/pointer conversions + ------------------------------------------------------------- + T# U# If the destination type has compatible + alignment and other storage requirements, + the pointer should be converted losslessly + and in a round-tripping manner to point to + a U. If it does not have compatible + requirements, the conversion is not + required to round trip safely, but should + still produce a valid pointer. + ------------------------------------------------------------- + pointer/slice conversions + ------------------------------------------------------------- + T[:] T# Returns a pointer to t[0] + ------------------------------------------------------------- + pointer/function conversions + ------------------------------------------------------------- + (args->ret) T# Returns a pointer to an implementation + specific value representing the executable + code for the function. + + + + 4.6.4. Assignment: + + 4.6.5. Bitwise Expressions: + + 4.6.6: Arithmetic Expressons: + + 4.6.7: Postfix Expressiosn: + + 4.6.8: Prefix Expressions 4.8. Packages and Uses: - pkg use + 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: @@ -628,21 +769,12 @@ TABLE OF CONTENTS: use syspkg use "localfile" - The unquoted form searches all system include paths for 'syspkg' - and imports it into the namespace. By convention, the namespace - defined by 'syspkg' is 'syspkg', and is unique and unmerged. This - is not enforced, however. Typical usage of unquoted names is to - import a library that already exists. - - The quoted form searches the local directory for "localpkg". By - convention, the package it imports does not match the name - "localpkg", but instead is used as partial of the definition of the - importers package. This is a confusing description. + 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. - A typical use of a quoted import is to allow splitting one package - into multiple files. In order to support this behavior, if a package - is defined in the current file, and a use statements imports a - package with the same namespace, the two namespaces are merged. + 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, @@ -660,6 +792,9 @@ TABLE OF CONTENTS: 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: 5.1. Data Types: @@ -685,11 +820,11 @@ TABLE OF CONTENTS: long ulong float32 float64 - These types are as you would expect. 'void' represents a - lack of type, although for the sake of genericity, you can - assign between void types, return values of void, and so on. - This allows generics to not have to somehow work around void - being a toxic type. The void value is named `void`. + 'void' is a type and a value although for the sake of + genericity, you can assign between void types, return values + of void, and so on. This allows generics to not have to + somehow work around void being a toxic type. The void value is + named `void`. It is interesting to note that these types are not keywords, but are instead merely predefined identifiers in the type @@ -699,10 +834,10 @@ TABLE OF CONTENTS: assigned, tested for equality, and used in the various boolean operators. - char is a 32 bit integer type, and is guaranteed to be able - to hold exactly one codepoint. It can be assigned integer - literals, tested against, compared, and all the other usual - numeric types. + char is a 32 bit integer type, and is guaranteed to hold + exactly one Unicode codepoint. It can be assigned integer + literals, tested against, compared, and all the other usual + numeric types. The various [u]intXX types hold, as expected, signed and unsigned integers of the named sizes respectively. |