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diff --git a/awk/scheme/scheme/docs/scheme-compiler-impl.md b/awk/scheme/scheme/docs/scheme-compiler-impl.md new file mode 100644 index 0000000..db8a204 --- /dev/null +++ b/awk/scheme/scheme/docs/scheme-compiler-impl.md @@ -0,0 +1,307 @@ +# Scheme Compiler Implementation in AWK + +## Basic Compiler Structure + +We'll implement the compiler as a recursive descent processor that converts Scheme expressions into VM instructions. Here's the core structure: + +```awk +# Global state +BEGIN { + next_label = 0 # For generating unique labels + next_address = 0 # Current instruction address + depth = 0 # Current environment depth +} + +# Main compile function +function compile(expr, parts, len) { + if (isAtom(expr)) + return compileAtom(expr) + + split(expr, parts, " ") + len = length(parts) + + # Strip parentheses + parts[1] = substr(parts[1], 2) # Remove leading ( + parts[len] = substr(parts[len], 1, length(parts[len])-1) # Remove trailing ) + + # Dispatch based on first element + if (parts[1] == "+") + return compileAdd(parts, len) + else if (parts[1] == "let") + return compileLet(parts, len) + else if (parts[1] == "lambda") + return compileLambda(parts, len) + else if (parts[1] == "if") + return compileIf(parts, len) + else + return compileCall(parts, len) +} + +# Utility functions +function isAtom(expr) { + return substr(expr, 1, 1) != "(" +} + +function newLabel() { + return "L" next_label++ +} + +function emit(instr) { + program[next_address++] = instr +} +``` + +## Compilation Patterns + +### 1. Basic Arithmetic + +```awk +function compileAdd(parts, len, i) { + # Compile each argument + for (i = 2; i <= len; i++) + compile(parts[i]) + + # Emit adds between each value + for (i = 3; i <= len; i++) + emit("ADD") + + return next_address - 1 +} + +# Example usage: +# Input: (+ 1 2 3) +# Output: +# PUSH_CONST N:1 +# PUSH_CONST N:2 +# ADD +# PUSH_CONST N:3 +# ADD +``` + +### 2. Let Expressions + +```awk +function compileLet(parts, len, bindings, body, i, num_bindings) { + # Parse let structure + bindings = parts[2] + body = parts[3] + + # Count bindings + split(bindings, binding_parts, " ") + num_bindings = (length(binding_parts) - 2) / 2 # Account for parentheses + + # Create new environment frame + emit("MAKE_ENV " num_bindings) + + # Compile each binding value and store + for (i = 1; i <= num_bindings; i++) { + compile(binding_parts[i * 2]) + emit("STORE_LOCAL " (i - 1)) + } + + # Compile body in new environment + depth++ + compile(body) + depth-- + + return next_address - 1 +} + +# Example usage: +# Input: (let ((x 5)) (+ x 1)) +# Output: +# MAKE_ENV 1 +# PUSH_CONST N:5 +# STORE_LOCAL 0 +# LOAD_LOCAL 0 +# PUSH_CONST N:1 +# ADD +``` + +### 3. Lambda Expressions + +```awk +function compileLambda(parts, len, param_list, body, label_start, label_end) { + label_start = newLabel() + label_end = newLabel() + + # Emit jump around function body + emit("JUMP " label_end) + + # Mark function start + emit(label_start ":") + + # Parse parameters + param_list = parts[2] + body = parts[3] + + # Compile function body + depth++ + compile(body) + emit("RETURN") + depth-- + + # Mark function end + emit(label_end ":") + + # Create function object + emit("MAKE_FUNCTION " label_start) + + return next_address - 1 +} + +# Example usage: +# Input: (lambda (x) (+ x 1)) +# Output: +# JUMP L1 +# L0: +# LOAD_LOCAL 0 +# PUSH_CONST N:1 +# ADD +# RETURN +# L1: +# MAKE_FUNCTION L0 +``` + +### 4. If Expressions + +```awk +function compileIf(parts, len, condition, true_branch, false_branch, label_else, label_end) { + label_else = newLabel() + label_end = newLabel() + + # Compile condition + compile(parts[2]) + + # Jump to else if false + emit("JUMP_IF_FALSE " label_else) + + # Compile true branch + compile(parts[3]) + emit("JUMP " label_end) + + # Compile false branch + emit(label_else ":") + if (len > 4) # If there is an else branch + compile(parts[4]) + + emit(label_end ":") + + return next_address - 1 +} + +# Example usage: +# Input: (if (< x 0) (- 0 x) x) +# Output: +# LOAD_LOCAL 0 +# PUSH_CONST N:0 +# NUM_LT +# JUMP_IF_FALSE L0 +# PUSH_CONST N:0 +# LOAD_LOCAL 0 +# SUB +# JUMP L1 +# L0: +# LOAD_LOCAL 0 +# L1: +``` + +### 5. Function Calls + +```awk +function compileCall(parts, len, i, num_args) { + num_args = len - 1 + + # Compile each argument + for (i = 2; i <= len; i++) + compile(parts[i]) + + # Compile function reference + compile(parts[1]) + + # Emit call instruction + emit("CALL " num_args) + + return next_address - 1 +} + +# Example usage: +# Input: (add1 5) +# Output: +# PUSH_CONST N:5 +# LOAD_GLOBAL 0 +# CALL 1 +``` + +## Symbol Table Management + +```awk +# Track variables and their locations +function enterScope() { + scope_depth++ + next_local = 0 +} + +function leaveScope() { + scope_depth-- +} + +function addLocal(name) { + symbols[scope_depth "," name] = next_local++ +} + +function findVariable(name, i) { + for (i = scope_depth; i >= 0; i--) + if ((i "," name) in symbols) + return "LOCAL " i "," symbols[i "," name] + return "GLOBAL " name +} +``` + +## Example Usage + +Here's how to use the compiler: + +```awk +BEGIN { + # Initialize compiler + next_label = 0 + next_address = 0 + depth = 0 + + # Compile some example code + expr = "(let ((x 5)) (+ x 1))" + compile(expr) + + # Print generated code + for (i = 0; i < next_address; i++) + print i ": " program[i] +} +``` + +## Implementation Notes + +1. Variable Resolution + - Track scope depth for proper variable lookup + - Generate appropriate LOAD/STORE instructions + - Handle closure captures + +2. Label Generation + - Use unique labels for control flow + - Track label addresses for jumps + +3. Environment Management + - Track environment depth + - Generate correct frame sizes + - Handle nested scopes + +4. Error Handling + - Check for syntax errors + - Validate number of arguments + - Report meaningful errors + +5. Optimization Opportunities + - Tail call detection + - Constant folding + - Peephole optimization + - Dead code elimination |