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Nested function parameters parsing issues

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CD

CodeParser_Dev

Posted on January 23, 2024 • Advanced

🔧 Nested function parameter parsing problem

Hey everyone! I’m building a custom programming language in Scratch and running into a complex issue with nested function calls. When I try to parse expressions like sqrt(abs(-3)+abs(-4)), the index keeps incrementing infinitely and never satisfies the stop condition.

The problem specifically occurs with:

  • Multiple nested function calls within one expression
  • Parameter parsing getting stuck in infinite loops
  • Index variables not behaving as expected

Simple nested functions like sqrt(abs(-3)+4) work fine, but multiple function nesting breaks everything. Any advanced programmers who can help debug this? 🤔

PS

Parser_Specialist

Replied 4 hours later • ⭐ Best Answer

Excellent question @CodeParser_Dev! This is a classic problem in language implementation. Let me break down the solution:

🔍 Function Parsing Flow

Here’s how nested function parsing should work:

flowchart TD A[📝 Input: sqrt(abs(-3)+abs(-4))] --> B[Find Function: sqrt] B --> C[Extract Parameters: abs(-3)+abs(-4)] C --> D[Parse Parameter String] D --> E{Contains Function?} E -->|Yes| F[🔄 Push Current State] E -->|No| G[✅ Simple Parameter] F --> H[Find Inner Function: abs] H --> I[Extract Inner Params: -3] I --> J[🔄 Recursive Parse] J --> K[Pop Previous State] K --> L[Continue with: +abs(-4)] L --> M{More Functions?} M -->|Yes| F M -->|No| N[✅ Complete Parse] G --> O[Return Value] N --> O style A fill:#e1f5fe style F fill:#fff3e0 style J fill:#f3e5f5 style K fill:#e8f5e8 style O fill:#fce4ec

🚨 The Core Problem: Variable Scope

The issue is that Scratch variables are global. When you have nested function calls, they overwrite each other’s index variables.

❌ What’s happening:

    // Function A starts parsing
set [index v] to [1]
// Function B (nested) overwrites index
set [index v] to [1]
// Function A loses its position!

🛠️ Solution: Stack-Based Variable Management

Implement a push/pop system for variable state:

    define push variable (variable name) (value)
add (join (variable name) [|] (value)) to [variable stack v]

define pop variable (variable name)
set [temp v] to []
repeat (length of [variable stack v])
set [item v] to (item (length of [variable stack v]) of [variable stack v])
if <(item (1) of (split (item) by [|])) = (variable name)> then
set [temp v] to (item (2) of (split (item) by [|]))
delete (length of [variable stack v]) of [variable stack v]
stop [this script v]
end
end

🔧 Step 1: Function Entry Management

Before processing any nested function:

    define enter function (function name)
push variable [index] (index)
push variable [depth] (depth)
push variable [current params] (current params)
change [depth v] by [1]
set [function stack v] to (join (function stack) (join [|] (function name)))

🔄 Step 2: Function Exit Management

When exiting a function:

    define exit function
set [index v] to (pop variable [index])
set [depth v] to (pop variable [depth])
set [current params v] to (pop variable [current params])
set [function stack v] to (join (all but last of (split (function stack) by [|])) [])

📊 Step 3: Parameter Parsing with State Management

Proper parameter extraction:

    define parse parameters (param string)
enter function [parse_params]
set [paren count v] to [0]
set [current param v] to []
set [param list v] to []

repeat (length of (param string))
set [char v] to (letter (index) of (param string))

if <(char) = [(]> then
change [paren count v] by [1]
end

if <(char) = [)]> then
change [paren count v] by [-1]
end

if <<(char) = [,]> and <(paren count) = [0]>> then
add (current param) to [param list v]
set [current param v] to []
else
set [current param v] to (join (current param) (char))
end

change [index v] by [1]
end

add (current param) to [param list v]
exit function

🎯 Step 4: Nested Function Detection

Identify and handle nested functions properly:

    define process nested functions (expression)
enter function [process_nested]
set [result v] to (expression)

repeat until <not <(result) contains [()]>>
set [func start v] to [0]
set [func end v] to [0]

// Find innermost function call
repeat (length of (result))
if <(letter (index) of (result)) = [(]> then
set [func end v] to (index)
set [func start v] to (index)
repeat until <<(letter (func start) of (result)) = [ ]> or <(func start) = [1]>>
change [func start v] by [-1]
end
change [func start v] by [1]
stop [this script v]
end
change [index v] by [1]
end

// Extract and evaluate function
set [function name v] to (letters (func start) to (func end - 1) of (result))
set [params v] to (letters (func end + 1) to (find [)] in (result) - 1) of (result))

// Recursively evaluate
set [func result v] to (evaluate function (function name) with (params))

// Replace in original expression
set [before v] to (letters [1] to (func start - 1) of (result))
set [after v] to (letters (find [)] in (result) + 1) to (length of (result)) of (result))
set [result v] to (join (before) (join (func result) (after)))
end

exit function

🔍 Step 5: Debug Logging System

Add comprehensive logging to track the parsing process:

    define log parsing (message) (data)
if <(debug mode) = [true]> then
add (join (join [DEPTH ] (depth)) (join [: ] (join (message) (join [ - ] (data))))) to [debug log v]
end

This stack-based approach ensures that each function call maintains its own state, preventing the infinite loop issue you’re experiencing! 🎉

CD

CodeParser_Dev

Replied 1 hour later

@Parser_Specialist This is absolutely brilliant! 🤯

I implemented the stack-based variable management and it completely solved the infinite loop issue. The push/pop system was exactly what I needed to maintain proper state across nested calls.

One follow-up question - how would you handle even deeper nesting levels, like sqrt(abs(sin(cos(45))))? Does the stack approach scale well?

RA

Recursion_Architect

Replied 3 hours later

@CodeParser_Dev Great question! The stack approach scales excellently for deep nesting. Here’s why:

    // Stack grows with nesting depth
// Level 1: sqrt(...)
// Level 2: abs(...)
// Level 3: sin(...)
// Level 4: cos(45)

// Each level maintains its own state
// Memory usage: O(depth) which is very efficient

For production systems, you might want to add a maximum recursion depth limit to prevent stack overflow:

    define check recursion depth
if <(depth) > [50]> then
set [error v] to [Maximum recursion depth exceeded]
stop [all v]
end

The beauty of this approach is that it mirrors how real programming languages handle function calls! 🎯

VB

Vibelf_Community

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