diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/sexp/mod.rs | 5 | ||||
| -rw-r--r-- | src/sexp/subst.rs | 21 | ||||
| -rw-r--r-- | src/sexp/util.rs | 5 |
3 files changed, 29 insertions, 2 deletions
diff --git a/src/sexp/mod.rs b/src/sexp/mod.rs index 087cb67..d866be5 100644 --- a/src/sexp/mod.rs +++ b/src/sexp/mod.rs @@ -1,12 +1,12 @@ pub mod step; pub mod util; +pub mod subst; /// A leaf node for S-Expressions. /// /// May represent built-in operators, -/// variables (to be added), functions -/// (to be added) or values. +/// variables, functions (to be added) or values. #[derive(Debug)] #[derive(PartialEq)] pub enum SLeaf { @@ -15,6 +15,7 @@ pub enum SLeaf { Mul, Div, Int(i32), + Var(String), } /// An S-Expression; the defining structure of the language. diff --git a/src/sexp/subst.rs b/src/sexp/subst.rs new file mode 100644 index 0000000..7cfa180 --- /dev/null +++ b/src/sexp/subst.rs @@ -0,0 +1,21 @@ + +use crate::sexp::{SExp, SExp::*, SLeaf::*, util::*}; + +impl SExp { + /// Performs substitution on the s-expression. + /// + /// Replaces all free occurrences of variables + /// named `name` with the given `value` + /// in this s-expression. + /// ```rust + /// use melisp::sexp::{SExp::*, SLeaf::*, util::*}; + /// + /// assert_eq!( + /// scons(Add, scons(var("a"), var("b"))).subst("b", scons(Sub, scons(2, 1))), + /// scons(Add, scons(var("a"), scons(Sub, scons(2, 1)))) + /// ); + /// ``` + pub fn subst(self, name: &str, value: SExp) -> SExp { + todo!(); + } +} diff --git a/src/sexp/util.rs b/src/sexp/util.rs index c31358f..ce6de5d 100644 --- a/src/sexp/util.rs +++ b/src/sexp/util.rs @@ -25,3 +25,8 @@ impl From<i32> for SLeaf { pub fn scons(x: impl Into<Box<SExp>>, y: impl Into<Box<SExp>>) -> SExp { SCons(x.into(), y.into()) } + +pub fn var(name: &str) -> SExp { + Atom(Var(name.to_string())) +} + |