Public API and docs

src/stl/str/char_at.rs

@@ -0,0 +1,45 @@
+use std::fmt::Debug;
+
+use super::super::litconv::{with_str, with_uint};
+use super::super::runtime_error::RuntimeError;
+use crate::representations::interpreted::{Clause, ExprInst};
+use crate::representations::{Literal, Primitive};
+use crate::{atomic_impl, atomic_redirect, externfn_impl};
+
+/// Takes an uint and a string, finds the char in a string at a 0-based index
+///
+/// Next state: [CharAt1]
+#[derive(Clone)]
+pub struct CharAt2;
+externfn_impl!(CharAt2, |_: &Self, x: ExprInst| Ok(CharAt1 { x }));
+
+/// Prev state: [CharAt2]; Next state: [CharAt0]
+#[derive(Debug, Clone)]
+pub struct CharAt1 {
+  x: ExprInst,
+}
+atomic_redirect!(CharAt1, x);
+atomic_impl!(CharAt1);
+externfn_impl!(CharAt1, |this: &Self, x: ExprInst| {
+  with_str(&this.x, |s| Ok(CharAt0 { s: s.clone(), x }))
+});
+
+/// Prev state: [CharAt1]
+#[derive(Debug, Clone)]
+pub struct CharAt0 {
+  s: String,
+  x: ExprInst,
+}
+atomic_redirect!(CharAt0, x);
+atomic_impl!(CharAt0, |Self { s, x }: &Self, _| {
+  with_uint(x, |i| {
+    if let Some(c) = s.chars().nth(i as usize) {
+      Ok(Clause::P(Primitive::Literal(Literal::Char(c))))
+    } else {
+      RuntimeError::fail(
+        "Character index out of bounds".to_string(),
+        "indexing string",
+      )?
+    }
+  })
+});