allow the last term in a pipe statement to be a variable, rewrites this as var = <rest of pipe>

compiler/src/prog8/compiler/astprocessing/AstChecker.kt

@@ -1285,11 +1285,11 @@ internal class AstChecker(private val program: Program,
 
             for(expr in expressions.drop(1)) {         // just keep the first expression value as-is
                 val functionName = expr as? IdentifierReference
-                val function = functionName?.targetStatement(program)
+                val target = functionName?.targetStatement(program)
-                if(functionName!=null && function!=null) {
+                if(functionName!=null && target!=null) {
-                    when (function) {
+                    when (target) {
                         is BuiltinFunctionPlaceholder -> {
-                            val func = BuiltinFunctions.getValue(function.name)
+                            val func = BuiltinFunctions.getValue(target.name)
                             if(func.parameters.size!=1)
                                 errors.err("can only use unary function", expr.position)
                             else if(!func.hasReturn && expr !== expressions.last())
@@ -1307,17 +1307,21 @@ internal class AstChecker(private val program: Program,
                             }
                         }
                         is Subroutine -> {
-                            if(function.parameters.size!=1)
+                            if(target.parameters.size!=1)
                                 errors.err("can only use unary function", expr.position)
-                            else if(function.returntypes.size!=1 && expr !== expressions.last())
+                            else if(target.returntypes.size!=1 && expr !== expressions.last())
                                 errors.err("function must return a single value", expr.position)
 
-                            val paramDt = function.parameters.firstOrNull()?.type
+                            val paramDt = target.parameters.firstOrNull()?.type
                             if(paramDt!=null && !(valueDt isAssignableTo paramDt))
                                 errors.err("pipe value datatype $valueDt incompatible with function argument $paramDt", functionName.position)
 
-                            if(function.returntypes.isNotEmpty())
+                            if(target.returntypes.isNotEmpty())
-                                valueDt = function.returntypes.single()
+                                valueDt = target.returntypes.single()
+                        }
+                        is VarDecl -> {
+                            if(!(valueDt isAssignableTo target.datatype))
+                                errors.err("final pipe value datatype can't be stored in pipe ending variable", functionName.position)
                         }
                         else -> {
                             throw FatalAstException("weird function")

compiler/src/prog8/compiler/astprocessing/StatementReorderer.kt

@@ -412,6 +412,26 @@ internal class StatementReorderer(val program: Program,
         checkUnusedReturnValues(functionCallStatement, function, program, errors)
         return tryReplaceCallWithGosub(functionCallStatement, parent, program, options)
     }
+
+    override fun after(pipe: Pipe, parent: Node): Iterable<IAstModification> {
+        val last = pipe.expressions.lastOrNull() as? IdentifierReference
+        val variable = last?.targetVarDecl(program)
+        if(variable!=null) {
+            val target = AssignTarget(last, null, null, last.position)
+            if(pipe.expressions.size>2)
+            {
+                val value = PipeExpression(pipe.expressions.dropLast(1).toMutableList(), pipe.position)
+                val assign = Assignment(target, value, AssignmentOrigin.OPTIMIZER, pipe.position)
+                return listOf(IAstModification.ReplaceNode(pipe, assign, parent))
+            }
+            else if(pipe.expressions.size==2)
+            {
+                val assign = Assignment(target, pipe.expressions[0], AssignmentOrigin.OPTIMIZER, pipe.position)
+                return listOf(IAstModification.ReplaceNode(pipe, assign, parent))
+            }
+        }
+        return noModifications
+    }
 }
 
 

compiler/test/TestPipes.kt

@@ -142,12 +142,44 @@ class TestPipes: FunSpec({
         value.number shouldBe 194.0
 
         assigncc = stmts[6] as Assignment
-        val pipecc = assignw.value as PipeExpression
+        val pipecc = assigncc.value as PipeExpression
         pipecc.expressions.size shouldBe 2
-        pipecc.expressions[0] shouldBe instanceOf<FunctionCallExpression>()
+        pipecc.expressions[0] shouldBe instanceOf<BuiltinFunctionCall>()
         pipecc.expressions[1] shouldBe instanceOf<IdentifierReference>()
     }
 
+    test("correct pipe expressions with variables at end") {
+        val text = """
+            %import textio
+            
+            main {
+                sub start() {
+                    uword @shared ww
+                    ubyte @shared cc
+                    
+                    9999 |> addword |> addword |> ww
+                    30 |> sin8u |> cos8u |> cc     ; will be optimized away into a const number
+                }
+                sub addword(uword ww) -> uword {
+                    return ww+2222
+                }
+        }
+        """
+        val result = compileText(C64Target(), true, text, writeAssembly = true).assertSuccess()
+        val stmts = result.program.entrypoint.statements
+        stmts.size shouldBe 7
+
+        val assignw = stmts[4] as Assignment
+        val pipew = assignw.value as PipeExpression
+        pipew.expressions.size shouldBe 2
+        pipew.expressions[0] shouldBe instanceOf<FunctionCallExpression>()
+        pipew.expressions[1] shouldBe instanceOf<IdentifierReference>()
+
+        val assigncc = stmts[5] as Assignment
+        val value = assigncc.value as NumericLiteral
+        value.number shouldBe 194.0
+    }
+
     test("incorrect type in pipe expression") {
         val text = """
             %option enable_floats

docs/source/programming.rst

@@ -701,12 +701,13 @@ If you want to ignore a return value of a subroutine, you should prefix the call
 Otherwise the compiler will issue a warning about discarding a result value.
 
 Deeply nested function calls can be rewritten as a chain using the *pipe operator* ``|>`` as long as they
-are unary functions (taking a single argument).
+are unary functions (taking a single argument). Various possibilities of using this operator are explained
+in the syntax reference for this operator.
 
 .. note::
     **Order of evaluation:**
 
-    The order of evaluation of arguments is *unspecified* and should not be relied upon.
+    The order of evaluation of arguments to a single function call is *unspecified* and should not be relied upon.
     There is no guarantee of a left-to-right or right-to-left evaluation of the call arguments.
 
 .. caution::

docs/source/syntaxreference.rst

@@ -549,6 +549,15 @@ pipe: ``|>``
                         |> determine_score
                         |> add_bonus
 
+    Finally, if you like the left-to-right flow, it's possible to use the name of a variable as the last term. This just means that the pipe's resulting value is
+    stored in that variable (it's just another way of writing an assignment). So the above can also be written as::
+
+        uword score
+        get_player(1)
+            |> determine_score
+            |> add_bonus
+            |> score
+
 address of:  ``&``
     This is a prefix operator that can be applied to a string or array variable or literal value.
     It results in the memory address (UWORD) of that string or array in memory:  ``uword a = &stringvar``

docs/source/todo.rst

@@ -3,7 +3,7 @@ TODO
 
 For next release
 ^^^^^^^^^^^^^^^^
-- allow the last term in a pipe *statement* to be a variable, rewrite this as   var = <rest of pipe>
+- sin8u(30) is different from sin8u(xx) where xx=30, so the const eval is off. Also test/fix other builtin functions!
 
 
 Need help with

examples/test.p8

@@ -3,13 +3,28 @@
 main {
     sub start() {
         ubyte xx = 30
-        ubyte cc
+        byte cc
 
-;        cc = 30 |> sin8u |> cos8u
+;        cc=0
+;        30 |> sin8u |> cos8u |> cc
 ;        txt.print_ub(cc)
 ;        txt.nl()
-        cc = xx |> sin8u |> cos8u
+;        cc=0
-        txt.print_ub(cc)
+;        xx |> sin8u |> cos8u |> cc
+;        txt.print_ub(cc)
+;        txt.nl()
+        100 |> cc
+        txt.print_b(cc)
+        txt.nl()
+        -100 |> abs |> abs |> cc
+        txt.print_b(cc)
+        txt.nl()
+        cc |> abs |> abs |> cc
+        txt.print_b(cc)
+        txt.nl()
+        cc = -100
+        cc |> abs |> abs |> cc
+        txt.print_b(cc)
         txt.nl()
 
         repeat {