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Advanced Constructs

This section covers implementing Y Lang's advanced language constructs using Inkwell, including lambda expressions, closures, method calls, and pattern matching patterns that require sophisticated LLVM IR generation.

Lambda Expressions and Function Values

Why lambdas need special handling: Lambda expressions create anonymous functions that can capture variables from their environment, requiring careful management of function pointers, closure environments, and calling conventions.

Basic Lambda Expression

Y Lang lambdas are first-class values that can be passed around and called:

#![allow(unused)]
fn main() {
use inkwell::context::Context;
use inkwell::types::BasicMetadataTypeEnum;

let context = Context::create();
let module = context.create_module("lambdas");
let builder = context.create_builder();

let i64_type = context.i64_type();
let ptr_type = context.ptr_type(Default::default());

// Lambda: |x: i64| -> i64 { x + 1 }
// Step 1: Create the lambda function
let lambda_param_types = vec![BasicMetadataTypeEnum::IntType(i64_type)];
let lambda_fn_type = i64_type.fn_type(&lambda_param_types, false);
let lambda_function = module.add_function("lambda_0", lambda_fn_type, None);

// Step 2: Implement lambda body
let lambda_entry = context.append_basic_block(lambda_function, "entry");
builder.position_at_end(lambda_entry);

let x_param = lambda_function.get_nth_param(0).unwrap().into_int_value();
let one = i64_type.const_int(1, false);
let result = builder.build_int_add(x_param, one, "add_one").unwrap();
builder.build_return(Some(&result)).unwrap();

// Step 3: Create function pointer value
let lambda_ptr = lambda_function.as_global_value().as_pointer_value();
}

Generated LLVM IR:

define i64 @lambda_0(i64 %0) {
entry:
  %add_one = add i64 %0, 1
  ret i64 %add_one
}

; Usage would involve function pointer: @lambda_0

Lambda with Variable Capture (Closures)

Closures capture variables from their enclosing scope, requiring environment structures:

#![allow(unused)]
fn main() {
// Y Lang: let y = 10; let closure = |x| x + y;
// This requires creating a closure environment

// Step 1: Define closure environment structure
let closure_env_type = context.struct_type(&[
    i64_type.into(), // captured variable 'y'
], false);

// Step 2: Create closure function that takes environment + parameters
let closure_param_types = vec![
    BasicMetadataTypeEnum::PointerType(closure_env_type.ptr_type(Default::default())), // env
    BasicMetadataTypeEnum::IntType(i64_type), // x parameter
];
let closure_fn_type = i64_type.fn_type(&closure_param_types, false);
let closure_function = module.add_function("closure_0", closure_fn_type, None);

// Step 3: Implement closure body
let closure_entry = context.append_basic_block(closure_function, "entry");
builder.position_at_end(closure_entry);

let env_param = closure_function.get_nth_param(0).unwrap().into_pointer_value();
let x_param = closure_function.get_nth_param(1).unwrap().into_int_value();

// Extract captured variable from environment
let y_ptr = builder.build_struct_gep(closure_env_type, env_param, 0, "y_ptr").unwrap();
let y_val = builder.build_load(i64_type, y_ptr, "y_val").unwrap().into_int_value();

// Compute x + y
let closure_result = builder.build_int_add(x_param, y_val, "x_plus_y").unwrap();
builder.build_return(Some(&closure_result)).unwrap();

// Step 4: Create closure environment at runtime
let y_value = i64_type.const_int(10, false);
let env_alloca = builder.build_alloca(closure_env_type, "closure_env").unwrap();
let y_field_ptr = builder.build_struct_gep(closure_env_type, env_alloca, 0, "y_field").unwrap();
builder.build_store(y_field_ptr, y_value).unwrap();

// Step 5: Create closure representation (function pointer + environment)
let closure_type = context.struct_type(&[
    closure_fn_type.ptr_type(Default::default()).into(), // function pointer
    closure_env_type.ptr_type(Default::default()).into(), // environment pointer
], false);

let closure_alloca = builder.build_alloca(closure_type, "closure").unwrap();
let fn_ptr_field = builder.build_struct_gep(closure_type, closure_alloca, 0, "fn_ptr_field").unwrap();
let env_ptr_field = builder.build_struct_gep(closure_type, closure_alloca, 1, "env_ptr_field").unwrap();

let closure_fn_ptr = closure_function.as_global_value().as_pointer_value();
builder.build_store(fn_ptr_field, closure_fn_ptr).unwrap();
builder.build_store(env_ptr_field, env_alloca).unwrap();
}

Generated LLVM IR:

%ClosureEnv = type { i64 }
%Closure = type { ptr, ptr }

define i64 @closure_0(ptr %0, i64 %1) {
entry:
  %y_ptr = getelementptr %ClosureEnv, ptr %0, i32 0, i32 0
  %y_val = load i64, ptr %y_ptr
  %x_plus_y = add i64 %1, %y_val
  ret i64 %x_plus_y
}

; Environment creation:
%closure_env = alloca %ClosureEnv
%y_field = getelementptr %ClosureEnv, ptr %closure_env, i32 0, i32 0
store i64 10, ptr %y_field

; Closure creation:
%closure = alloca %Closure
%fn_ptr_field = getelementptr %Closure, ptr %closure, i32 0, i32 0
%env_ptr_field = getelementptr %Closure, ptr %closure, i32 0, i32 1
store ptr @closure_0, ptr %fn_ptr_field
store ptr %closure_env, ptr %env_ptr_field

Calling Closures

Closures are called by extracting their function pointer and environment:

#![allow(unused)]
fn main() {
// Call closure: closure(42)
let arg_value = i64_type.const_int(42, false);

// Extract function pointer and environment
let fn_ptr_ptr = builder.build_struct_gep(closure_type, closure_alloca, 0, "fn_ptr_ptr").unwrap();
let env_ptr_ptr = builder.build_struct_gep(closure_type, closure_alloca, 1, "env_ptr_ptr").unwrap();

let fn_ptr = builder.build_load(closure_fn_type.ptr_type(Default::default()), fn_ptr_ptr, "fn_ptr").unwrap().into_pointer_value();
let env_ptr = builder.build_load(closure_env_type.ptr_type(Default::default()), env_ptr_ptr, "env_ptr").unwrap().into_pointer_value();

// Call with environment and arguments
let call_args = vec![env_ptr.into(), arg_value.into()];
let call_result = builder.build_indirect_call(closure_fn_type, fn_ptr, &call_args, "closure_call").unwrap();
}

Generated LLVM IR:

%fn_ptr_ptr = getelementptr %Closure, ptr %closure, i32 0, i32 0
%env_ptr_ptr = getelementptr %Closure, ptr %closure, i32 0, i32 1
%fn_ptr = load ptr, ptr %fn_ptr_ptr
%env_ptr = load ptr, ptr %env_ptr_ptr
%closure_call = call i64 %fn_ptr(ptr %env_ptr, i64 42)

Method Calls and Object-Oriented Patterns

Why method calls need special handling: Y Lang method calls require dynamic dispatch, self parameter handling, and potentially virtual function tables for polymorphism.

Simple Method Call

Method calls pass the receiver as the first parameter:

#![allow(unused)]
fn main() {
// Y Lang: point.distance_from_origin()
// Where point is a struct with x, y fields

// Method function: fn distance_from_origin(self: &Point) -> f64
let point_type = context.struct_type(&[i64_type.into(), i64_type.into()], false);
let f64_type = context.f64_type();

let method_param_types = vec![
    BasicMetadataTypeEnum::PointerType(point_type.ptr_type(Default::default())), // &self
];
let method_fn_type = f64_type.fn_type(&method_param_types, false);
let method_function = module.add_function("Point_distance_from_origin", method_fn_type, None);

// Implement method body
let method_entry = context.append_basic_block(method_function, "entry");
builder.position_at_end(method_entry);

let self_param = method_function.get_nth_param(0).unwrap().into_pointer_value();

// Load x and y fields
let x_ptr = builder.build_struct_gep(point_type, self_param, 0, "x_ptr").unwrap();
let y_ptr = builder.build_struct_gep(point_type, self_param, 1, "y_ptr").unwrap();

let x_val = builder.build_load(i64_type, x_ptr, "x").unwrap().into_int_value();
let y_val = builder.build_load(i64_type, y_ptr, "y").unwrap().into_int_value();

// Convert to float for calculation
let x_float = builder.build_signed_int_to_float(x_val, f64_type, "x_float").unwrap();
let y_float = builder.build_signed_int_to_float(y_val, f64_type, "y_float").unwrap();

// Calculate sqrt(x^2 + y^2)
let x_squared = builder.build_float_mul(x_float, x_float, "x_squared").unwrap();
let y_squared = builder.build_float_mul(y_float, y_float, "y_squared").unwrap();
let sum_squares = builder.build_float_add(x_squared, y_squared, "sum_squares").unwrap();

// Call sqrt intrinsic
let sqrt_intrinsic = module.get_function("llvm.sqrt.f64").unwrap_or_else(|| {
    let sqrt_fn_type = f64_type.fn_type(&[BasicMetadataTypeEnum::FloatType(f64_type)], false);
    module.add_function("llvm.sqrt.f64", sqrt_fn_type, None)
});

let sqrt_result = builder.build_call(sqrt_intrinsic, &[sum_squares.into()], "distance").unwrap()
    .try_as_basic_value().left().unwrap();

builder.build_return(Some(&sqrt_result)).unwrap();

// Method call: point.distance_from_origin()
let point_alloca = builder.build_alloca(point_type, "point").unwrap();
// ... initialize point ...

let method_result = builder.build_call(method_function, &[point_alloca.into()], "method_call").unwrap();
}

Generated LLVM IR:

define double @Point_distance_from_origin(ptr %0) {
entry:
  %x_ptr = getelementptr { i64, i64 }, ptr %0, i32 0, i32 0
  %y_ptr = getelementptr { i64, i64 }, ptr %0, i32 0, i32 1
  %x = load i64, ptr %x_ptr
  %y = load i64, ptr %y_ptr
  %x_float = sitofp i64 %x to double
  %y_float = sitofp i64 %y to double
  %x_squared = fmul double %x_float, %x_float
  %y_squared = fmul double %y_float, %y_float
  %sum_squares = fadd double %x_squared, %y_squared
  %distance = call double @llvm.sqrt.f64(double %sum_squares)
  ret double %distance
}

; Method call:
%method_call = call double @Point_distance_from_origin(ptr %point)

Method Chaining

Method chaining requires careful handling of return values:

#![allow(unused)]
fn main() {
// Y Lang: builder.add(1).multiply(2).build()
// Each method returns self or a new value

// Methods that return self for chaining
let builder_type = context.struct_type(&[i64_type.into()], false); // { value: i64 }

// add method: fn add(mut self, n: i64) -> Self
let add_method_params = vec![
    BasicMetadataTypeEnum::PointerType(builder_type.ptr_type(Default::default())), // &mut self
    BasicMetadataTypeEnum::IntType(i64_type), // n
];
let add_method_type = context.void_type().fn_type(&add_method_params, false);
let add_method = module.add_function("Builder_add", add_method_type, None);

let add_entry = context.append_basic_block(add_method, "entry");
builder.position_at_end(add_entry);

let self_param = add_method.get_nth_param(0).unwrap().into_pointer_value();
let n_param = add_method.get_nth_param(1).unwrap().into_int_value();

// Modify self.value += n
let value_ptr = builder.build_struct_gep(builder_type, self_param, 0, "value_ptr").unwrap();
let current_value = builder.build_load(i64_type, value_ptr, "current").unwrap().into_int_value();
let new_value = builder.build_int_add(current_value, n_param, "new_value").unwrap();
builder.build_store(value_ptr, new_value).unwrap();

builder.build_return(None).unwrap(); // Void return, self is modified in place

// Chained call: builder.add(1).multiply(2)
let builder_alloca = builder.build_alloca(builder_type, "builder").unwrap();

// First call: builder.add(1)
builder.build_call(add_method, &[builder_alloca.into(), i64_type.const_int(1, false).into()], "add_call").unwrap();

// Second call on same object: .multiply(2)
// multiply_method implementation would be similar...
}

Pattern Matching

Why pattern matching is complex: Pattern matching requires decision trees, value extraction, and exhaustiveness checking while maintaining efficient branching.

Simple Pattern Matching

Y Lang pattern matching on enums and values:

#![allow(unused)]
fn main() {
// Y Lang enum: enum Option<T> { None, Some(T) }
// Pattern match: match option { None => 0, Some(x) => x }

// Represent Option<i64> as tagged union
let option_type = context.struct_type(&[
    context.i8_type().into(),  // tag: 0 = None, 1 = Some
    i64_type.into(),           // value (only valid for Some)
], false);

// Pattern matching function
let match_param_types = vec![BasicMetadataTypeEnum::StructType(option_type)];
let match_fn_type = i64_type.fn_type(&match_param_types, false);
let match_function = module.add_function("match_option", match_fn_type, None);

let entry_block = context.append_basic_block(match_function, "entry");
let none_block = context.append_basic_block(match_function, "match_none");
let some_block = context.append_basic_block(match_function, "match_some");
let merge_block = context.append_basic_block(match_function, "merge");

builder.position_at_end(entry_block);

let option_param = match_function.get_nth_param(0).unwrap().into_struct_value();

// Extract tag field
let tag_value = builder.build_extract_value(option_param, 0, "tag").unwrap().into_int_value();

// Switch on tag
let zero_tag = context.i8_type().const_int(0, false);
let one_tag = context.i8_type().const_int(1, false);

let is_none = builder.build_int_compare(IntPredicate::EQ, tag_value, zero_tag, "is_none").unwrap();
builder.build_conditional_branch(is_none, none_block, some_block).unwrap();

// None case: return 0
builder.position_at_end(none_block);
let none_result = i64_type.const_int(0, false);
builder.build_unconditional_branch(merge_block).unwrap();

// Some case: extract and return value
builder.position_at_end(some_block);
let some_value = builder.build_extract_value(option_param, 1, "some_value").unwrap().into_int_value();
builder.build_unconditional_branch(merge_block).unwrap();

// Merge results
builder.position_at_end(merge_block);
let result_phi = builder.build_phi(i64_type, "match_result").unwrap();
result_phi.add_incoming(&[
    (&none_result, none_block),
    (&some_value, some_block),
]);

builder.build_return(Some(&result_phi.as_basic_value())).unwrap();
}

Generated LLVM IR:

define i64 @match_option({ i8, i64 } %0) {
entry:
  %tag = extractvalue { i8, i64 } %0, 0
  %is_none = icmp eq i8 %tag, 0
  br i1 %is_none, label %match_none, label %match_some

match_none:
  br label %merge

match_some:
  %some_value = extractvalue { i8, i64 } %0, 1
  br label %merge

merge:
  %match_result = phi i64 [ 0, %match_none ], [ %some_value, %match_some ]
  ret i64 %match_result
}

Complex Pattern Matching with Guards

Pattern matching with additional conditions:

#![allow(unused)]
fn main() {
// Y Lang: match (x, y) { (0, _) => "zero x", (_, 0) => "zero y", (a, b) if a == b => "equal", _ => "other" }

// This requires multiple decision points and guard evaluation
let tuple_type = context.struct_type(&[i64_type.into(), i64_type.into()], false);
let str_type = context.ptr_type(Default::default()); // String representation

let complex_match_type = str_type.fn_type(&[BasicMetadataTypeEnum::StructType(tuple_type)], false);
let complex_match = module.add_function("complex_match", complex_match_type, None);

let entry = context.append_basic_block(complex_match, "entry");
let check_x_zero = context.append_basic_block(complex_match, "check_x_zero");
let check_y_zero = context.append_basic_block(complex_match, "check_y_zero");
let check_equal = context.append_basic_block(complex_match, "check_equal");
let case_x_zero = context.append_basic_block(complex_match, "case_x_zero");
let case_y_zero = context.append_basic_block(complex_match, "case_y_zero");
let case_equal = context.append_basic_block(complex_match, "case_equal");
let case_other = context.append_basic_block(complex_match, "case_other");
let merge = context.append_basic_block(complex_match, "merge");

builder.position_at_end(entry);
let tuple_param = complex_match.get_nth_param(0).unwrap().into_struct_value();

// Extract tuple elements
let x = builder.build_extract_value(tuple_param, 0, "x").unwrap().into_int_value();
let y = builder.build_extract_value(tuple_param, 1, "y").unwrap().into_int_value();

builder.build_unconditional_branch(check_x_zero).unwrap();

// Check if x == 0
builder.position_at_end(check_x_zero);
let zero = i64_type.const_int(0, false);
let x_is_zero = builder.build_int_compare(IntPredicate::EQ, x, zero, "x_is_zero").unwrap();
builder.build_conditional_branch(x_is_zero, case_x_zero, check_y_zero).unwrap();

// Check if y == 0 (and x != 0)
builder.position_at_end(check_y_zero);
let y_is_zero = builder.build_int_compare(IntPredicate::EQ, y, zero, "y_is_zero").unwrap();
builder.build_conditional_branch(y_is_zero, case_y_zero, check_equal).unwrap();

// Check if x == y (guard condition)
builder.position_at_end(check_equal);
let x_equals_y = builder.build_int_compare(IntPredicate::EQ, x, y, "x_equals_y").unwrap();
builder.build_conditional_branch(x_equals_y, case_equal, case_other).unwrap();

// Case implementations would create string constants and branch to merge...
// Each case creates its result and branches to merge block with PHI node
}

Advanced Optimization Patterns

Tail Call Optimization

For recursive lambdas and functions:

#![allow(unused)]
fn main() {
// Enable tail call optimization for recursive calls
let recursive_call = builder.build_call(function, &args, "tail_call").unwrap();
recursive_call.set_tail_call(true);

// This helps LLVM optimize recursive patterns
}

Inline Assembly for Performance Critical Code

When Y Lang needs low-level operations:

#![allow(unused)]
fn main() {
// Inline assembly for special operations
let asm_type = context.void_type().fn_type(&[i64_type.into()], false);
let inline_asm = context.create_inline_asm(
    asm_type,
    "nop".to_string(),
    "r".to_string(),
    true,  // has side effects
    false, // is align stack
    None,
);

builder.build_call(inline_asm, &[i64_type.const_int(42, false).into()], "asm_call").unwrap();
}

Function Specialization

Creating specialized versions of generic functions:

#![allow(unused)]
fn main() {
// Template: fn map<T, U>(arr: [T], f: T -> U) -> [U]
// Specialized: fn map_i64_to_f64(arr: [i64], f: i64 -> f64) -> [f64]

fn specialize_function(
    context: &Context,
    module: &Module,
    generic_name: &str,
    type_args: &[BasicTypeEnum]
) -> FunctionValue {
    // Generate specialized function name
    let specialized_name = format!("{}_{}", generic_name, mangle_types(type_args));

    // Create specialized function with concrete types
    // Implementation depends on the specific generic function

    // Return specialized function
    module.get_function(&specialized_name).unwrap()
}
}

Error Handling in Advanced Constructs

Safe Pattern Matching

Ensure exhaustiveness and prevent runtime errors:

#![allow(unused)]
fn main() {
fn validate_pattern_match(
    patterns: &[Pattern],
    input_type: &Type
) -> Result<(), String> {
    // Check pattern exhaustiveness
    if !is_exhaustive(patterns, input_type) {
        return Err("Pattern match is not exhaustive".to_string());
    }

    // Validate pattern types
    for pattern in patterns {
        if !pattern.matches_type(input_type) {
            return Err(format!("Pattern {:?} doesn't match type {:?}", pattern, input_type));
        }
    }

    Ok(())
}
}

Closure Environment Validation

Ensure captured variables are valid:

#![allow(unused)]
fn main() {
fn validate_closure_capture(
    captured_vars: &[Variable],
    closure_scope: &Scope
) -> Result<(), String> {
    for var in captured_vars {
        if !closure_scope.can_capture(var) {
            return Err(format!("Cannot capture variable {:?} in closure", var.name));
        }

        if var.is_moved() {
            return Err(format!("Cannot capture moved variable {:?}", var.name));
        }
    }

    Ok(())
}
}

This comprehensive coverage of advanced constructs provides the foundation for implementing Y Lang's sophisticated language features in LLVM, emphasizing proper memory management, type safety, and optimization considerations for complex control patterns.