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If-then-else

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Smaug123
2024-01-22 19:22:36 +00:00
parent 4275b5caa7
commit 6c26bcb5eb
3 changed files with 33 additions and 1 deletions
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13
PrattParser.Test/TestParser.fs
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@@ -16,7 +16,18 @@ module TestParser =
"-a!", Expr.unaryMinus (Expr.factorial (Expr.var "a"))
"-a! + b", Expr.plus (Expr.unaryMinus (Expr.factorial (Expr.var "a"))) (Expr.var "b")
"(-a)! + b", Expr.plus (Expr.factorial (Expr.paren (Expr.unaryMinus (Expr.var "a")))) (Expr.var "b")
// TODO: if-then-else
"if x then y else z", Expr.ifThenElse (Expr.var "x") (Expr.var "y") (Expr.var "z")
"if x then y", Expr.ifThen (Expr.var "x") (Expr.var "y")
"1 + if x then y", Expr.plus (Expr.constInt 1) (Expr.ifThen (Expr.var "x") (Expr.var "y"))
"if x + 1 then y else z + 3",
Expr.ifThenElse
(Expr.plus (Expr.var "x") (Expr.constInt 1))
(Expr.var "y")
(Expr.plus (Expr.var "z") (Expr.constInt 3))
"(if x + 1 then y else z) + 3",
Expr.plus
(Expr.paren (Expr.ifThenElse (Expr.plus (Expr.var "x") (Expr.constInt 1)) (Expr.var "y") (Expr.var "z")))
(Expr.constInt 3)
"g x y + a * (func b c)",
let gXY =

3
PrattParser/Domain.fs
View File

@@ -12,6 +12,7 @@ type Expr =
| Factorial of Expr
| Paren of Expr
| IfThenElse of Expr * Expr * Expr
| IfThen of Expr * Expr
[<RequireQualifiedAccess>]
module Expr =
@@ -28,6 +29,8 @@ module Expr =
let ifThenElse ifClause thenClause elseClause =
Expr.IfThenElse (ifClause, thenClause, elseClause)
let ifThen ifClause thenClause = Expr.IfThen (ifClause, thenClause)
[<RequireQualifiedAccess>]
type TokenType =
| Plus

18
PrattParser/Parser.fs
View File

@@ -71,6 +71,24 @@ module Parser =
Expr.paren contents, rest
elif firstToken.Type = TokenType.If then
let ifClause, rest = parseInner inputString rest 0
match rest with
| [] -> failwith "if requires a trailing then"
| head :: _ when head.Type <> TokenType.Then -> failwithf "if was not followed by then, got: %+A" head
| _ :: rest ->
let thenClause, rest = parseInner inputString rest 0
match rest with
| [] -> Expr.ifThen ifClause thenClause, rest
| head :: _ when head.Type <> TokenType.Else -> Expr.ifThen ifClause thenClause, rest
| _ :: rest ->
let elseClause, rest = parseInner inputString rest 0
Expr.ifThenElse ifClause thenClause elseClause, rest
else
match Token.prefixPrecedence firstToken.Type with