From 2184f7e654fab17f25569f323f14426a9d608a0b Mon Sep 17 00:00:00 2001
From: Araozu <fernando@araozu.dev>
Date: Sun, 21 Jan 2024 15:06:53 -0500
Subject: [PATCH] Parse function parameters

---
 CHANGELOG.md              |  3 +-
 src/syntax/ast/mod.rs     |  5 +++
 src/syntax/params_list.rs | 92 ++++++++++++++++++++++++++++++++++++++-
 3 files changed, 98 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2ce1906..74bd57f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## TODO
 
 - Parse __more__ binary operators
+- Parse `Type name = value` bindings
 - Parse more complex bindings
 - Watch mode
 - Improve error messages
@@ -21,7 +22,7 @@
 
 - [x] Parse function call parameters
 - [x] Codegen function call parameters
-- [ ] Parse function declaration arguments
+- [x] Parse function declaration arguments (Type id)
 - [ ] Begin work on semantic analysis
 - [ ] Symbol table
 - [ ] Typecheck bindings
diff --git a/src/syntax/ast/mod.rs b/src/syntax/ast/mod.rs
index 1a309c9..cbd6da1 100644
--- a/src/syntax/ast/mod.rs
+++ b/src/syntax/ast/mod.rs
@@ -29,6 +29,11 @@ pub struct Block {
 #[derive(Debug)]
 pub struct ParamsList {}
 
+pub struct Parameter {
+    pub identifier: Box<String>,
+    pub datatype: Box<String>,
+}
+
 #[derive(Debug)]
 pub enum Expression {
     Number(Box<String>),
diff --git a/src/syntax/params_list.rs b/src/syntax/params_list.rs
index ca57547..43c8804 100644
--- a/src/syntax/params_list.rs
+++ b/src/syntax/params_list.rs
@@ -4,7 +4,10 @@ use crate::{
     syntax::utils::parse_token_type,
 };
 
-use super::{ast::ParamsList, ParseResult};
+use super::{
+    ast::{Parameter, ParamsList},
+    utils, ParseResult,
+};
 
 pub fn parse_params_list<'a>(
     tokens: &'a Vec<Token>,
@@ -21,6 +24,36 @@ pub fn parse_params_list<'a>(
         };
     current_pos = next_pos;
 
+    // Parse parameters definitions, separated by commas
+    let mut parameters = Vec::<Parameter>::new();
+    loop {
+        let (next_parameter, next_pos) = match parse_param_definition(tokens, current_pos) {
+            ParseResult::Ok(parameter, next_pos) => (parameter, next_pos),
+            ParseResult::Err(error) => {
+                return ParseResult::Err(error);
+            }
+            _ => break,
+        };
+        current_pos = next_pos;
+        parameters.push(next_parameter);
+
+        // Parse comma. This also parses a trailing comma
+        match parse_token_type(tokens, current_pos, TokenType::Comma) {
+            ParseResult::Ok(_, next) => {
+                current_pos = next;
+            }
+            // This should never happen
+            ParseResult::Err(err) => return ParseResult::Err(err),
+            ParseResult::Mismatch(_) => {
+                // Something other than a comma was found. It must be a closing paren )
+                // Still, break the loop, assume there are no more arguments
+                // TODO: This could be a good place to write a detailed error?
+                break;
+            }
+            ParseResult::Unmatched => break,
+        };
+    }
+
     // Parse closing paren
     let (_closing_paren, next_pos) =
         match parse_token_type(tokens, current_pos, TokenType::RightParen) {
@@ -45,3 +78,60 @@ pub fn parse_params_list<'a>(
 
     ParseResult::Ok(ParamsList {}, current_pos)
 }
+
+fn parse_param_definition<'a>(
+    tokens: &'a Vec<Token>,
+    pos: usize,
+) -> ParseResult<Parameter, &Token> {
+    // Parse a single parameter definition of the form:
+    // - Type identifier
+    // There will be more constructs in the future, like:
+    // - Type identifier = default_value
+    // - FunctionType identifier
+    // - Pattern identifier (e.g. Some[String] value)?
+
+    let mut current_pos = pos;
+    let (datatype, next_pos) =
+        match utils::parse_token_type(tokens, current_pos, TokenType::Datatype) {
+            ParseResult::Ok(token, next) => (token, next),
+            ParseResult::Err(err) => {
+                return ParseResult::Err(err);
+            }
+            // If there is no datatype this construction doesn't apply.
+            // Return a mismatch and let the caller handle it
+            ParseResult::Mismatch(t) => return ParseResult::Mismatch(t),
+            ParseResult::Unmatched => return ParseResult::Unmatched,
+        };
+    current_pos = next_pos;
+
+    let (identifier, next_pos) =
+        match utils::parse_token_type(tokens, current_pos, TokenType::Identifier) {
+            ParseResult::Ok(token, next) => (token, next),
+            ParseResult::Err(err) => {
+                return ParseResult::Err(err);
+            }
+            // However, if we fail to parse an identifier, it's an error
+            ParseResult::Mismatch(_) => {
+                return ParseResult::Err(SyntaxError {
+                    reason: String::from("Expected an identifier for the parameter."),
+                    error_start: tokens[pos].position,
+                    error_end: tokens[pos].get_end_position(),
+                });
+            }
+            ParseResult::Unmatched => {
+                return ParseResult::Err(SyntaxError {
+                    reason: String::from("Expected an identifier for the parameter."),
+                    error_start: tokens[pos].position,
+                    error_end: tokens[pos].get_end_position(),
+                })
+            }
+        };
+
+    ParseResult::Ok(
+        Parameter {
+            identifier: Box::new(identifier.value.clone()),
+            datatype: Box::new(datatype.value.clone()),
+        },
+        next_pos,
+    )
+}