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diff --git a/chapter24/README.md b/chapter24/README.md new file mode 100644 index 00000000..03056897 --- /dev/null +++ b/chapter24/README.md @@ -0,0 +1,345 @@ + + +## Unifying Structs and Arrays + +The idea is that structs have fields indexed by names, and arrays have fields +indexed by numbers, and these ideas are compatible with each other. This idea +has been used by the C language for a long time - an array can follow a normal +struct C and can index it with the usual array syntax. + +The alternative, using a field to hold a pointer to an array, exchanges some +flexibility for an extra indirection. The obvious flexibility allows swapping +the array out (generally for a larger one) and this is the basis of very common +`Vector` or `ArrayList` generic containers. + + +```java +struct str { + int hash; // A cache of the strings hash code + u32 #; // The array length + u8 []; // Array of bytes +}; + +str X = "abc"; +print(X.hash); // Read the hash field +X[0]=='a'; // Read array element 0 +X#; // Length of the array + +``` + +Here, the field named `#` holds the array length and the field named `[]` is +the actual array, which follows the other fields directly in memory. +Here is another example for variable length array: + +```java +struct vecInt { + u32 size; // Actual number of elements + u32 #; // The array length or capacity + int []; // Array of integers. +}; +``` + +The obvious limit here is that the array cannot be directly resized; it is +literally in the same memory block as the leading fields. Such a `vecInt` can +be *re-allocated* to a new larger `vecInt`, but the original `vecInt` will be +reclaimed - you cannot use the same `vecInt` reference forever. + +Any number of named fields are allowed: + +```java +struct Class { + str className; + str professor; + int time; + int credits; + Class prerequisite; + u16 #; // Limit of 65535 students per class + Student []; +}; +``` + +Or self-reference: + +```java +struct NTree { + Some val; + u8 #; // Length is 0-255 + NTree []; // More NTrees +}; +``` + +The syntax rules are: +- the last field is named `[]` and can be of any type. +- the second-to-last field is named `#` and must be some unsigned integer type + representing the maximum array length. +- may require a leading space in front of ` []` + + + +### Constructors and Arrays + +The allocation includes the array length, and can include a constructor: +`new NTree{val=17;}[2];` + +The constructor is optional, the array length is not. + +Optional function for initializing arrays, allows for write-once final arrays: +`new u8[buffer#,{ u32 idx -> buffer[idx].toUpperCase() }]` + + + +### Changing array max length + +An issue for large numbers of range-checked small arrays is that reserving a +full 4 bytes for array length can substantially increase the array overhead. +Simple allows for arrays to have smaller max lengths, although these are +treated as a different type than arrays with different max lengths. + +```java +struct x0 { u8 #; u8[]; }; // Array limited to 0-255 length +struct x1 { u16 #; u8[]; }; // Array limited to 0-65535 length +struct x2 { u32 #; u8[]; }; // +struct x3 { u64 #; u8[]; }; // + +x0 x = "abc"; // 4 bytes total: [3, 'a', 'b', 'c'] +x1 y = "def"; // 6 bytes total: [3, 0 , 'd', 'e', 'f', 0,]; 1 pad byte to acheieve 2-byte alignment +x = y; // ERROR, "x1 is not x0", no auto-widening +x += y; // OK, 7 bytes total: [6, 'a', 'b', 'c', 'd', 'e', 'f'] +y += x; // OK, 8 bytes total: [6, 0 , 'd', 'e', 'f', 'a', 'b', 'c'] + +x += "VeryLongString.... ....255_chars"; // Runtime RangeCheck + +// Explicit conversion to widen string +y = "" + x; +``` + + +### Two flavors of extendable arrays/strings: an extra indirection or not + +With an extra indirection you get e.g. Java `ArrayList` or C++ `Vector`. + +Without, then any call which extends the extendable array return a potentially +new object, only growing as needed. + +```java +val vec1 = new vecInt[0].add(2); // len=1, capacity=1 +val vec2 = vec1.add(3); // NEW vecInt returned, only is deleted; len=2; capacity=2; +vec1[0]; // ERROR, vec1 has been freed by call to `vec1.add(3)` +vec2[0]; // OK +vec2[1]; // OK +vec2[2]; // Runtime error, AIOOBE +``` + + +## A String Implementation + +Default strings have names like "str", "cstr", "ustr" or such. + +Always unicode8 with explicit u8 manipulations. Unicode "characters" will come +as function calls over the base implementation, probably in another string class. + +## Default string + +Efficiently growable via concantenation. Supports a variety of IO/printf functions. +The underlying array can be shared mutable if you ask for this. +The defaults will always be private mutable and read-only shared. + +```java +struct str { + + // Add a string to the string, possibly growing + val add = { str str -> + val self = this; + for( int i=0; i<str#; i++ ) + self = self.add(str[i]); + return self; + }; + + // Add an char to the string, possibly growing + val add = { u8 e -> + if( len >= # ) return copy(# ? #*2 : 1).add(e); + [size++] = e; + return this; + }; + + // Copy 'this' to a new larger size + val copy = { int sz2 -> + val v2 = new str[sz2]; + for( int i=0; i<len; i++ ) + v2[i] = [i]; + v2.len = len; + sys.libc.free(this); // Needs a better Mem Management solution + return v2; + }; + + val print { -> sys.libc.write(1/*stdout*/,[]/*array base as argument to C*/,len); return this; } + + u32 len; // In-use size + u32 #; // Max length is 4Gig, although variants can request smaller lengths + u8 []; // Character data +}; +``` + + +### A Final String + +Intended to be a **immutable** string, possibly used as a base for a **secure** +string. This needs to be created all at once, and probably requires a +defensive copy. + +```java +struct sstr { + // Possible static call syntax; no references to "this" + val make { str str -> new sstr[str#,str.at] }; + + // Array contents are immutable. + // Still figuring out good syntax for this. + u8 #; + u8 [~]; // Middlin '~'? Makes primitive array contents *immutable* and requires constructor syntax +}; + +// Construction requires a function that produces the array contents. +// Here we are defining a defensive copy over `buf`. +sstr safe = new sstr[buf.len,{ int idx -> buf[idx]; }]; +sstr safe = sstr.make("abc"); // Defensive copy is made +``` + + +### A Extendable String (aka StringBuilder or StringBuffer) + +This API is intended to be a drop-in for a `StringBuilder` style, and takes an +extra indirection with each usage. + +```java +struct xstr { + str !_str; // The extra indirection is here + val add = { str str -> _str = str.add2(str); }; + val write = { int fd -> _str.write(fd); }; +}; +``` + +### A Unicode String + +This API is intended to support unicode character manipulation over a plain `str` + +```java +struct ustr { + // Assuming idx is at the start of a character, return the character + // as a 32b integer. Returns junk integer if not at a character start. + // For all ASCII strings this will amount to a simple byte load. + // For bytes with high order bits set, this may read 1-4 characters. + val at = { int idx -> ... }; +}; +// Unicode character iterator +struct ucharator { +// Return successive unicode character codes +}; +``` + +### A "C" string + +A zero-terminated string, but the length has to be available directly + +```java +struct cstr { + u8 #; // length including the trailing zero + u8[]; // always ends in a zero byte; suitable for direct passing to C string functions +}; +``` + +### A "german string": a very short string that can exist in a register + +Length in memory is 1 byte (3 bits?) of length, then 0-7 chars; max 8 chars. +Fits in a 64 bit register. + +```java +struct gstr { // aka germanString, or blend string and register "streg" + u3 #; // Size is 0-7 bytes??? + u8 []; // Up to 7 bytes +} +// Using inlined object (see below). All these strings are short and are +// represented as packed integers in a 64b register. +*gstr prize1 = "gold"; +*gstr prize2 = "silver"; +*gstr prize3 = "bronze"; + +``` + +### Main becomes `val main = { str[] args -> ...}` + + +## Structs can be inlined + +Structs are normally by-reference, but can be converted to by-value by using +the `*` operator, pronounced "contents of" (this name might be changed to +e.g. `inline`). + +This is a name-space change only, you cannot take the address of the internal +struct without entirely consuming its lifetime. No "escaping". + +```java +// 2 64-bit words, no other overheads +struct Complex { f64 x,y; val len = { ->Math.sqrt(x*x+y*y); }; }; + +// Current Simple rules: always by-reference +struct ByRef { + Complex c; // 4-byte pointer to a Complex +}; +print(new ByRef.c.y); // Lookup requires 1 extra memory load from ref to c + +// New behavior: by value (inlining a struct) +// The '*' syntax indicator can be something else, e.g. a keyword "inline" +// I am pronouncing '*' as "contents of" +struct ByValue { + *Complex c; // c is inlined, full 16 bytes into ByValue +}; +print(new ByValue.c.y); // x,y inlined into ByValue, no extra memory load + +// Mixing Refs and Struct Values. Basically, a ref can be converted +// to a value by taking the "contents of" the ref, and values cannot +// be *converted* to a ref, although they can be copied over a ref. +ref. c = val.c; // Error, mixing refs and values +ref.*c = val.c; // Allowed, whole structure copy. Does not allocate, requires ref.c not-null +val. c = ref.c; // Error, mixing refs and values +val. c = *ref.c; // Allowed, whole structure copy +ref. c = ref.c; // Allowed, pointer copy +val. c = val.c; // Allowed, whole structure copy. +val *c = val.c; // Error, cannot take "contents of" a value + +// Alternative syntax, to avoid the "contents of" being on LHS and field applying to being on RHS: +ref.c = val.*c; // Assign into ref.c the "contents of" val.c + +// Arrays of inlined structures +var ary = new *Complex[99]; // Array of 99 Complex objects, inlined + +// Calling methods has the same syntax +ref.c.len(); +val.c.len(); + +// Function arguments use the same typing, so can pass-by-value +val math.sin = { *Complex c -> ... }; // Passes a complex by value +math.sin(ref.*c); // Requires de-reference to pass by value +math.sin(val. c); // Pass by value + +``` + + + +## RoadMap for other chapters + +`&&` and `||` +Drop `int` to `i32`. +Drop `TypeMemPtr` to 4 bytes; using `mmap` to make heap in low 4G. +Add optimistic pass SCCP to `opto` +Default parser for-loop construction, or partial peel. + `for( init; test; next ) body` +becomes: +```java +{ init; // Normal scope entry to bound lifetime of index variable +if( !test ) { // Zero-trip count test + do { + body; + next; + } while( test ); // Exit test at loop bottom by default +} }; +``` |