Update spec

spec.txt

@@ -50,7 +50,7 @@ Literals:
     'a'    -> u8 (ascii only?)
     '猫'u  -> u32
 
-TODO: string literals? fixed-size arrays? built-in spans? Probably built-in spans (potentially defined in prelude.psl)
+// TODO: string literals? fixed-size arrays? built-in spans? Probably built-in spans (defined in prelude.psl)
     "hello, world" -> utf-8 string
     "здарова, братки"u -> utf-32 string
 
@@ -72,7 +72,7 @@ Array declaration:
 Null pointer literal:
     let p: u32* = null      // special like empty array literal, type cannot be inferred
 
-Variables must always be initialized. (TODO: really? What about arrays? Maybe need special syntax for zero-initialization or mass-initialization. Alternative: default to zero-initialization)
+Variables must always be initialized. // TODO: really? What about arrays? Maybe need special syntax for zero-initialization or mass-initialization. Alternative: default to zero-initialization
 Const variables must be initialized with a const expression (any expression that doesn't include non-const values).
 
 ======== OPERATORS ========
@@ -126,7 +126,7 @@ Casting:
 
 The only implicit casting allowed is T mut* -> T* (maybe?)
 Any integer/floating-point types can be cast to each other.
-Any pointer types can be cast to each other (TODO: alignment? UB or safe fallback? Probably UB.)
+Any pointer types can be cast to each other // TODO: alignment? UB or safe fallback? Probably UB.
 
 Ternary if operator:
     if condition then true_value else false_value
@@ -150,7 +150,7 @@ Special built-ins:
 
 ======== FLOW CONTROL ========
 
-Flow control:
+Conditionals:
     if condition:
         statements
     else if condition:
@@ -158,6 +158,7 @@ Flow control:
     else:
         statements
 
+While loop:
     while condition:
         statements
         if x:
@@ -165,7 +166,38 @@ Flow control:
         if y:
             continue
 
-    TODO: for loops? iterator/range interface?
+Iterator interface:
+    get(it) returns the currently pointed-to value
+    get_ref(it) returns the pointer to the currently pointed-to value
+    next(it) returns the next iterator
+
+Range interface:
+    begin(range) returns the begin iterator
+    end(range) returns the end iterator
+
+For loop:
+    Operates only on ranges.
+    
+    for x in range(10):
+        do_something(x)
+
+    i is immutable within the loop body.
+
+    Modifiable ranges use special syntax for pointers to elements:
+
+    for &x in array:
+        *x += 1
+
+    The loop is equivalent to
+
+    mut begin = begin(range)
+    let end = end(range)
+    while begin != end:
+        let x = get(begin) // or get_ref(x) for pointer loop
+        statements
+        begin = next(begin)
+
+    The prelude contains an implementation of range interface for built-in arrays.
 
 ======== STRUCTS ========
 
@@ -184,7 +216,7 @@ Struct field access:
     let p = &r
     let y = p.height // field access through pointer is the same
 
-TODO: inner struct functions maybe? to act as namespace/module containers
+// TODO: inner struct functions maybe? to act as namespace/module containers
 
 ======== FUNCTIONS ========
 
@@ -195,12 +227,37 @@ Function definition:
     func bar(x: f32): // deduced return type unit
         print(x)
 
+    Function arguments are automatically immutable (as if declared with let).
+
     // External function: name taken literally as `powf`
     // and C calling convention assumed
     foreign func powf(x: f32, y: f32) -> f32 // no implementation
 
-TODO: function overloading? Probably requires selecting a specific overload using `as` operator to save to a value (but not on call site)
-TODO: alternative - Rust-like traits? More powerful, but complicates the language
+// TODO: mutable function arguments?
+
+// TODO: function overloading? Probably requires selecting a specific overload using `as` operator to save to a value (but not on call site)
+// TODO: alternative - Rust-like traits, aka parametric polymorphism?
+
+======== TEMPLATES ========
+
+// TODO
+// Definitely monomorphized.
+// Parametric (C++ templates) vs ad-hoc (Rust traits, Haskell typeclasses)?
+//
+// Ad-hoc:
+//   + More powerful
+//   + Less concepts in the core language
+//   + Simpler to use in basic cases
+//   - Bad error messages (can be improved with concepts)
+//   - Slow compilation (due to type-checking each instantiation)
+//
+// Parametric:
+//   + Cleaner, stricter
+//   + Faster compilation (type-checking only once)
+//   + Better error messages
+//   - Less powerful
+//   - Harder to use in basic cases (e.g. have to declare type constraints or create new traits for any desired per-type behavior)
+//   - A bunch of new required language concepts (trait, impl, constraint), much more complicated to implement in compiler
 
 ======== TYPE OF TYPES ========
 
@@ -233,10 +290,50 @@ E.g.
 //         else:
 //             return y
 
+======== PRELUDE ========
+
+Prelude is a special source file implicitly included in any project (unless explicitly requested otherwise).
+
+It contains:
+
+    An array_view template struct:
+
+        struct array_view<t: type>:
+            size: u64
+            data: t*
+
+    A specialization for strings:
+
+        const string_view = array_view<u8>
+
+    (String literals compile into string_view objects.)
+
+    Range interface for built-in arrays and for array_view.
+
+    Numeric ranges with signatures
+
+        range(end) // begin implicitly zero
+        range(begin, end) // step implicitly one
+        range(begin, end, step)
+    
+    that allow iteration like
+
+        for i in range(10):
+        for i in range(5u, 10u):
+        for i in range(1.0, 10.0, 0.5):
+
 ======== MODULES AND IMPORTS ========
 
 // TODO
+// A build system / package metadata? How to e.g. conditionally add some files based on environment (maybe just forbid that)?
+// How to describe platform-dependent behavior?
+//   * Different files - who decides which files to include?
+//   * Compile-time built-ins - how flexible are they? 
+//     Can we create a different type based on platform? 
+//     Important for some posix stuff like timespec or threads
+//   * Special compiler intrinsics/attributes/macros/whatever - need a new concept in the language
+//     Maybe a good thing - can merge with alignment specification and other stuff
 
 ======== STANDARD LIBRARY ========
 
-// TODO: containers, memory management, strings?
+// TODO: containers, memory management, strings, io, math, threads, networking(?)